Wheat genetic resources enhancement by the International Maize and Wheat Improvement Center (CIMMYT

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RESEARCH ARTICLE1

2 Wheat genetic resources enhancement by the International

3 Maize and Wheat Improvement Center (CIMMYT)

4 Rodomiro Ortiz Hans-Joachim Braun Jose Crossa Jonathan H. Crouch

5 Guy Davenport John Dixon Susanne Dreisigacker Etienne Duveiller

6 Zhonghu He Julio Huerta Arun K. Joshi Masahiro Kishii Petr Kosina

7 Yann Manes Monica Mezzalama Alexei Morgounov Jiro Murakami

8 Julie Nicol Guillermo Ortiz Ferrara J. Ivan Ortiz-Monasterio Thomas S. Payne

9 R. Javier Pena Matthew P. Reynolds Kenneth D. Sayre Ram C. Sharma

10 Ravi P. Singh Jiankang Wang Marilyn Warburton Huixia Wu Masa Iwanaga111213 Received: 7 April 2008 / Accepted: 25 August 200814 � Springer Science+Business Media B.V. 2008

15 Abstract The International Maize and Wheat

16 Improvement Center (CIMMYT) acts as a catalyst

17 and leader in a global maize and wheat innovation

18 network that serves the poor in the developing world.

19 Drawing on strong science and effective partnerships,

20 CIMMYT researchers create, share, and use knowl-

21 edge and technology to increase food security,

22 improve the productivity and profitability of farming

23 systems and sustain natural resources. This people-

24 centered mission does not ignore the fact that

25 CIMMYT’s unique niche is as a genetic resources

26 enhancement center for the developing world, as

27 shown by this review article focusing on wheat.

28CIMMYT’s value proposition resides therefore in its

29use of crop genetic diversity: conserving it, studying

30it, adding value to it, and sharing it in enhanced form

31with clients worldwide. The main undertakings

32include: long-term safe conservation of world heri-

33tage of both crop resources for future generations, in

34line with formal agreements under the 2004 Interna-

35tional Treaty on Plant Genetic Resources for Food

36and Agriculture, understanding the rich genetic

37diversity of two of the most important staples

38worldwide, exploiting the untapped value of crop

39genetic resources through discovery of specific,

40strategically-important traits required for current

41and future generations of target beneficiaries, and

42development of strategic germplasm through innova-

43tive genetic enhancement. Finally, the Center needs

44to ensure that its main products reach end-users and

45improve their livelihoods. In this regard, CIMMYT is

46the main international, public source of wheat seed-

47embedded technology to reduce vulnerability and

48alleviate poverty, helping farmers move from subsis-

49tence to income-generating production systems.

50Beyond a focus on higher grain yields and value-

51added germplasm, CIMMYT plays an ‘‘integrative’’

52role in crop and natural resource management

53research, promoting the efficient use of water and

54other inputs, lower production costs, better manage-

55ment of biotic stresses, and enhanced system

56diversity and resilience.

A1 R. Ortiz (&) � H.-J. Braun � J. Crossa � J. H. Crouch �

A2 G. Davenport � J. Dixon � S. Dreisigacker �

A3 E. Duveiller � Z. He � J. Huerta � M. Kishii � P. Kosina �

A4 Y. Manes � M. Mezzalama � A. Morgounov �

A5 J. Murakami � J. Nicol � G. Ortiz Ferrara �

A6 J. I. Ortiz-Monasterio � T. S. Payne � R. J. Pena �

A7 M. P. Reynolds � K. D. Sayre � R. C. Sharma �

A8 R. P. Singh � J. Wang � M. Warburton � H. Wu �

A9 M. IwanagaA10 Centro Internacional de Mejoramiento de Maız y TrigoA11 (CIMMYT), Km. 45 Carretera Mexico-Veracruz,A12 Col. El Batan, Texcoco, Edo. de Mexico 56130, MexicoA13 e-mail: [email protected]

A14 A. K. JoshiA15 Department of Genetics and Plant Breeding, Institute ofA16 Agricultural Sciences, Banaras Hindu University,A17 Varanasi, UP, India

123

Journal : Medium 10722 Dispatch : 29-8-2008 Pages : 46

Article No. : 9372 h LE h TYPESET

MS Code : GRES951 h CP h DISK4 4

Genet Resour Crop Evol

DOI 10.1007/s10722-008-9372-4

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57 Keywords Triticum � Biofortification �

58 Climate change � Food safety � Genetic broadening �

59 Modeling � Participatory varietal selection �

60 Plant breeding � Rusts � Scab

Abbreviations

61 AA Association analysis

62 ARI Advanced research institutes

63 BNI Biological nitrification inhibition

64 CAZS-NR Center for Arid Zone Studies-Natural

Resources

65 CGIAR Consultative Group on International

Agricultural Research

66 CIMMYT Centro Internacional de

Mejoramiento de Maız y Trigo

67 CTD Canopy temperature depression

68 CWANA Central and West Asia and Northern

Africa

69 DON Deoxynivalenol

70 FAO Food and Agriculture Organization

of the United Nations

71 FAWWON Facultative and Winter Wheat

Observation Nursery

72 FHB Fusarium head blight

73 FONTAGRO Fondo Regional de Tecnologıa

Agropecuaria

74 GBSSI Granule-bound starch synthase

75 GE Genotype-by-environment

76 ICAR Indian Council of Agricultural

Research

77 ICARDA International Center for Agricultural

Research in the Dry Areas

78 ITPGRFA International Treaty on Plant Genetic

Resources for Food and Agriculture

79 IWIN International Wheat Improvement

Network

80 MEs Mega-environments

81 IWWIP International Winter Wheat

Improvement Program

82 LD Linkage disequilibrium

83 MAS Marker-assisted selection

84 MODPED Modified pedigree/bulk method

85 NARS National Agricultural Research

Systems

86 NIRS Near-infrared spectroscopy

87 NIV Nivalenol

88 OSS Office of Special Studies

89 OSU Oregon State University

90 PCR Polymerase chain reaction

91PVS Participatory variety selection

92QTL Quantitative trait loci

93RWC Rice-Wheat Consortium for the

Indo-Gangetic Plains

94SAGARPA Secretarıa de Agricultura Ganaderıa.

Desarrollo Rural Pesca y

Alimentacion (Mexico)

95SELBLK Selected bulk method

96SHL Seed Health Laboratory

97SMTA Standard Material Transfer

Agreement

98RCT Resource conserving technology

99ZEN Zearalenone

100

101Wheat general overview

102For millennia wheat has provided daily sustenance for

103a large proportion of the world’s population. It is

104produced in a wide range of climatic environments

105and geographic regions (Table 1). During 2004–2006,

106the global annual harvested area of ‘‘bread wheat’’ and

107‘‘durum wheat’’ averaged 217 million ha, producing

108621 million t of grain with a value of approximately

109US$ 150 billion. About 116 million ha of wheat was

110grown in developing countries, producing 308 mil-

111lion t of grain (FAO 2007) with a value of

112approximately US$ 75 billion. Wheat serves a wide

113range of demands for different end-uses, including

114staple food for a large proportion of the world’s poor

115farmers and consumers. The similarity between

116average yields in developed and developing regions

117is deceptive: in developed countries around 90% of

118the wheat area is rainfed while in developing countries

119more than half of the wheat area is irrigated,

120especially in the large producers (India and China).

121In addition, there are large differences in productivity

122between countries within the two groups of countries,

123and even between countries deploying similar agro-

124nomic practices. For instance, among major rainfed

125producers (over 1 million ha) the average national

126yield ranges from about 0.9 t ha-1 in Kazakhstan to

1272.6 t ha-1 in Canada, and up to 7.9 t ha-1 in the

128United Kingdom (FAO 2007). Similarly, contrasts are

129seen amongst irrigated producers, e.g. India has an

130average yield of 2.6 t ha-1 vis-a-vis 6.5 t ha-1 in

131Egypt. Thus, there is clearly considerable scope for

132increasing productivity in many countries.


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133 The relative importance of wheat as a staple in

134 selected countries is displayed in Fig. 1. Wheat

135 provides 500 kcal of food energy capita-1 day-1 in

136 the two most populous countries in the world, China

137 and India, and over 1,400 kcal capita-1 day-1 in Iran

138 and Turkey. Overall across in the developing world,

13916% of total dietary calories come from wheat (cf.

14026% in developed countries) second only to rice in

141importance. As the most traded food crop interna-

142tionally, wheat is the single largest food import into

143developing countries and, also, a major portion of

144emergency food aid.

Table 1 Area andproductivity of wheat inselected regions (2004–2006)

Source: FAO (2007)

Region Area(million ha)

Yield(t ha-1)

Production(million t)

European Union 27 26 5.3 137

East Asia 23 4.3 98

South Asia (including 2.2 million ha in Afghanistan) 38 2.5 97

North America 31 2.8 88

South America 9 2.4 22

Middle East and North Africa (including Turkey) 27 2.3 61

Eastern Europe and Russia 31 2.2 69

Central Asia and Caucasus 15 1.4 22

Australia and New Zealand 13 1.5 19

Other (including 3 million ha in sub-Saharan Africa) 4 2.3 9

World 217 2.9 621

Developing countries 116 2.7 308

Developed countries (incl. former-USSR) 101 3.1 313

Country contrasts

…dominated by rainfed production

Kazakhstan 12 0.9 12

Canada 10 2.6 27

United Kingdom 2 7.9 15

…dominated by irrigated production

India 26 2.6 70

Egypt 1 6.5 8

0

500

1000

1500

2000

2500

3000

3500

4000

4500

China

India

USA

Rus

sian

Franc

e

Can

ada

Ger

man

y

Turke

y

Pakista

n

Austra

lia

Ukr

aine U

KIra

n

Argen

tina

Kazak

hsta

n

Polan

d

Egypt

Italy

Rom

ania

Uzb

ekista

n

Kcal/cap

ita/d

ay

All foods

Wheat

minimum daily requirement

Fig. 1 Wheat share in foodconsumption in selectedcountries (Source data:FAO 2007)


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145 Wheat made a significant contribution to the

146 increase in global food production during the past

147 four decades as total production rose steadily through

148 the use of higher-yielding, water and fertilizer-

149 responsive and disease-resistant cultivars supported

150 by strengthened input delivery systems, tailored

151 management practices, and improved marketing

152 (Braun et al. 1998; Dixon et al. 2006) The increased

153 grain production attributable to improved germplasm

154 alone has been valued at up to US$ 6 billion year-1

155 (Lantican et al. 2005). The increased production of

156 wheat (and other staples) led to lower food prices

157 (von Braun 2007), which contributed to a reduction in

158 the proportion of poor in developing countries (Chen

159 and Ravallion 2007). Looking to the future, the

160 global population is projected to steadily increase,

161 albeit at a decreasing rate compared to the past

162 century, to around nine billion in 2050. The food and

163 other needs of the growing population underpin the

164 strong demand for cereals. The demand for wheat,

165 based on production and stock changes, is expected

166 to increase from 621 million t during 2004–2006 to

167 760 million tons in 2020 (Rosegrant et al. 2001), to

168 around 813 million t in 2030, and to more than

169 900 million t in 2050 (FAO 2006, 2007; Rosegrant

170 et al. 2007) implying growth rates of 1.6% for 2005–

171 2020, 1.2% for 2005–2030, and 0.9% for 2005–2050.

172 The International Wheat Improvement Network

173 The history of the International Maize and Wheat

174 Improvement Center (CIMMYT) involvement in

175 wheat improvement begins in the 1940s, more than

176 20 years before it was officially founded as an

177 international organization in 1966 (Ortiz et al.

178 2007b). Its roots reach back to the Office of Special

179 Studies (OSS), a research project sponsored by the

180 Mexican government and the Rockefeller Foundation

181 that was dedicated to improving maize, beans and

182 wheat, and later potatoes. The OSS began as a

183 research and training program focused on Mexico,

184 but soon began collaborating with other countries,

185 especially in South America. The OSS developed the

186 key organizational principles that would eventually

187 become central to the entire network of the Consul-

188 tative Group on International Agricultural Research

189 (CGIAR) centers. The OSS wheat program, led by

190 Nobel Peace Laureate Norman E. Borlaug, did crop

191breeding along with on-farm research and extension

192demonstrations aimed at introducing new technology

193to producers.

194For many decades the global average yield of

195wheat has increased, supported by an effective

196International Wheat Improvement Network (IWIN),

197an alliance of National Agricultural Research Systems

198(NARS), CIMMYT, the International Center for

199Agricultural Research in the Dry Areas (ICARDA)

200and advanced research institutes (ARI). This alliance

201has deployed cutting-edge science alongside practical

202multi-disciplinary applications resulting in the devel-

203opment of germplasm, which has improved food

204security and the livelihoods of farmers in developing

205countries. For example, during the late 1950s and

2061960s, researchers in Mexico, under the leadership of

207Borlaug, developed the improved spring wheat germ-

208plasm, which launched the Green Revolution in India,

209Pakistan, and Turkey (Reynolds and Borlaug 2006).

210Collaboration was broadened during the 1970s to

211include Brazil, China, and other major developing

212country producers, and resulted in wheat cultivars

213with broader disease resistance, better adaptation to

214marginal environments, and tolerance to acid soils.

215During the 1980s, an international collaborative

216partnership between Turkey, CIMMYT, and ICAR-

217DA was established for winter wheat improvement in

218developing countries. The IWIN currently operates

219field evaluation trials in more than 250 locations in

220around 100 countries for testing improved lines of

221wheat in different environments.

222As a publicly-funded international research insti-

223tute, CIMMYT regards its research products as

224international public goods. The main objective for

225regional and global multi-location testing is the

226identification of useful genetic diversity that will lead

227to research products, parental germplasm, or ulti-

228mately cultivars adapted to targeted wheat-production

229environments and systems in the developing world.

230Multi-location testing and data exchange increase the

231selection efficiency of participating wheat breeders.

232Returned data are used to identify parents for

233subsequent crosses and to incorporate new genetic

234variability into advanced lines that are consequently

235able to cope with the dynamics of abiotic and biotic

236stresses affecting wheat farming systems.

237With the growing research capacity of NARS in

238many major wheat-producing countries, the number

239of wheat cultivars released annually by developing


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240 countries doubled to more than 100 cultivars by the

241 early 1990s (Lantican et al. 2005). The early era of

242 improved cultivars spread rapidly over the high

243 potential production areas in most developing

244 regions. Widespread adoption occurred most rapidly

245 in South Asia, especially in irrigated areas, followed

246 by the rainfed areas of Latin America; adoption has

247 been slower in the Middle East, North Africa, and

248 sub-Saharan Africa because of drier riskier environ-

249 ments and weaker institutions (Evenson and Gollin

250 2003; Lantican et al. 2005). With such widespread

251 adoption accompanied by yield increases, average

252 annual rates of return for investments in wheat

253 research averaged around 50% year-1 (Alston et al.

254 2000). In addition, the urban poor benefited substan-

255 tially as production increases drove down wheat

256 prices.

257 The wheat genetic resources endowment

258 By the 1920s it was acknowledged that wheat

259 cultigens of the genus Triticum L. belonged to three

260 ploidy groups with chromosomes number of

261 2n = 2x = 14 (T. monococcum L.), 28 (T. turgidum

262 L. and T. timopheevii Zhuk.), and 42 (T. aestivum L.

263 em. Thell. and T. zhukovskyi Menabde & Ericz.).

264 However, world wheat production is almost entirely

265 based on two species: T. aestivum—also known as

266 common or bread wheat, which account for about

267 95% of world production, and T. turgidum ssp. durum

268 (Desf.) Husn.—known as macaroni or durum wheat,

269 which accounts for the remaining 5%. The other

270 cultivated species are largely historical relics.

271 Genetic resources in wheat can be categorized into

272 six broad groups (Frankel 1977; FAO 1983), namely

273 modern cultivars in current use, obsolete cultivars—

274 often the elite cultivars of the past and often found in

275 the pedigrees of modern cultivars, landraces, wild

276 relatives of crop species in the Triticeae Dumort. tribe,

277 genetic and cytogenetic stocks, and breeding lines.

278 These genetic resources represent the gene pool

279 potentially available to breeders and other users of

280 collections. This broad pool can be further subdivided

281 into primary, secondary, and tertiary gene pools

282 (Harlan and de Wet 1971). The primary pool consists

283 of the biological species, including cultivated, wild,

284 and weedy forms of the crop, and gene transfer in this

285 group is considered to be easy. The secondary gene

286pool has the coenospecies (or a group of ‘‘allies’’ or

287‘‘relatives’’ to a given taxon) from which gene transfer

288is possible but difficult, while the tertiary gene pool is

289composed of species from which gene transfer is

290possible but only with great difficulty. Clearly, the

291boundaries of these groups are fuzzy and also change

292with changes in technology. Consequently, several

293authors including Smartt (1984) and Konarev et al.

294(1986) have suggested the gene pools concept of

295Harlan and De Wet (1971) be modified to increase the

296number of gene pools from three to four to coincide

297with populations, species, genera, and tribes, respec-

298tively (Merezhko 1998). Unfortunately, even this

299simple concept is difficult to apply in wheat because

300of the lack of an accepted view on the classification of

301wheat species, the genus Triticum, and even the tribe

302Triticeae (von Bothmer et al. 1992; Merezhko 1998).

303The Wheat Genetics Resource Center at Kansas State

304University in the USA provides a comprehensive

305online source of information about wheat taxonomy,

306including a detailed comparison of the most often

307used classifications, as part of the GrainTax project

308(www.k-state.edu/wgrc/). Herein we will follow the

309most recent taxonomic treatment of Triticum and

310Aegilops L. of van Slageren (1994), which updated

311previous research by Hammer (1980) on the taxon-

312omy and nomenclature of the genus Aegilops.

313The cultivated species of Triticum and their

314genomic constitution are given in Table 2. It should

315be noted that there are two valid biological species at

316each ploidy level. The diploid T. monococcum L. has

317both cultivated and wild forms, while T. urartu

318Tumanian only exists in the wild. Both tetraploid

319forms exist in both cultivation and in the wild, while

320both hexaploid species only exist in cultivation.

321The distribution of these species is described by Gill

322and Friebe (2002). Aegilops is the most closely related

323genus to Triticum and has been widely used in

324wheat improvement. All Aegilops are annuals. The

325genus consists of 11 diploid species and 12 poly-

326ploid species, including tetraploids and hexaploids

327(Table 3). Their taxonomy and distribution is

328discussed by van Slageren (1994). Dasypyrum

329[Haynaldia] villosum (L.) Cand. is among the Triti-

330ceae species and is also a genetic resource for wheat

331breeding. It is an annual with a V genome and is easily

332hybridized to durum or bread wheat. Each of the

333chromosomes was added to common wheat by the late

334E. Sears (Global Crop Diversity Trust 2007).


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335 In addition to Aegilops, a host of more distantly

336 related annual and perennial members of related

337 genera in the Triticeae have potential as sources of

338 germplasm in wheat breeding including cultivated

339 rye and barley and their near relatives, as well as a

340 host of perennial grasses. The bulk of the perennial

341 Triticeae species have been difficult to exploit in

342 wheat improvement primarily because their genomes

343 are non-homologous to those of wheat, and genetic

344 transfers cannot be made by homologous recombi-

345 nation. However, gene transfer is possible via

346 complex cytogenetic protocols. Over the last three

347 decades hybridization per se has become less of a

348 problem in inter-specific hybridization between

349 Triticum species and more distantly related genera,

350 although achieving timely practical outcomes using

351 cytogenetic techniques is difficult in genera other

352 than Secale L. and Thinopyrum (Mujeeb-Kazi and

353 Rajaram 2002). Nevertheless, variation for econom-

354 ically-important traits such as host plant resistance to

355the cereal rusts, salt-tolerance, and resistance to

356barley yellow dwarf virus have been transferred from

357perennial wild species into bread wheat. The disease-

358resistant genes have been used in modern wheat

359cultivars. Mujeeb-Kazi and Hettel (1995) provided a

360comprehensive account of interspecific hybridization

361in the Triticeae. The perennial genera of the tribe

362Triticeae of interest in wheat improvement are given

363in Table 4 along with their genome designations and

364ploidy levels. All the genomes of the perennial

365Triticeae have been combined with the A, B, and D

366genomes of bread wheat (Mujeeb-Kazi 1995).

367Wheat ex situ conservation strategy

368Due to the strategic importance of wheat in food

369security and trade in many countries, and the critical

370importance of breeding in ensuring national industries

371remain competitive, over 80 autonomous germplasm

Table 2 Species of genusTriticum and their genomicconstitution (After Gill andFriebe 2002)

a Related to S-genomespecies, cf. Table 3

Species Genomic constitution

Nuclear Organellar

Triticum aestivum L. ABD B (rel. to S)a

Triticum aestivum ssp. aestivum (common or bread wheat)

Triticum aestivum ssp. compactum (Host) Mackey (club wheat)

Triticum aestivum ssp. macha (Dekapr. & A. M. Menabde) Mackey

Triticum aestivum ssp. Spelta (L.) Thell. (large spelt or dinkel wheat)

Triticum aestivum ssp. sphaerococcum (Percival) Mackey (Indian dwarf wheat)

Triticum turgidum L. AB B (rel. to S)

Triticum turgidum ssp. carthlicum (Nevski) A. Love & D. Love (Persian wheat)

Triticum turgidum ssp. dicoccoides (Korn. ex Asch. et Graebn.) Thell. (wild emmer)

Triticum turgidum ssp. dicoccon (Schrank) Thell. (emmer wheat)

Triticum turgidum ssp. durum (Desf.) Husn. (macaroni or durum wheat)

Triticum turgidum ssp. paleocolchicum (Dekapr. et Menabde) Mac Key ex Hanelt

Triticum turgidum ssp. polonicum (L.) Thell. (Polish wheat)

Triticum turgidum ssp. turanicum (Jakubz.) A. Love & D. Love (Khorassan wheat)

Triticum turgidum ssp. turgidum (pollard wheat)

Triticum zhukovskyi Menabde & Ericz. AtAmG A (rel. to S)

Triticum timopheevii (Zhuk.) Zhuk. AtG G (rel. to S)

Triticum timopheevii ssp. Armeniacum (Jakubz.) Slageren (wild form)

Triticum timopheevii ssp. timopheevii (cultivated form)

Triticum monococcum L. Am Am

Triticum monococcum ssp. aegilopoides (Link) Thell. (wild form)

Triticum monococcum ssp. monococcum (einkorn or small spelt wheat)

Triticum urartu Tumanian ex Gandilyan (wild form) A A


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372 collections holding an estimated excess of 800,000

373 accessions have been established globally. These

374 collections vary in size and coverage; the largest have

375 over 100,000 accessions and the smallest a few

376 hundred. They also vary greatly in coverage. Most

377 collections evolved from breeders’ working collec-

378 tions and carry predominantly local or regional

379 cultivars—advanced, obsolete or landrace—as well

380 as introduced cultivars of interest to national or

381 regional breeders. There is often substantial duplica-

382 tion within, and certainly between these sorts of

383 collections. Virtually every wheat collection in the

384 world would carry common popular cultivars such as

385 ‘Marquis’ and ‘Bezostaya 1.’ However, there are also

386 numerous small specialist collections of wild wheat

387 relatives and genetic stocks.

388An important issue in developing a global strategy

389for the conservation of wheat genetic resources is

390deciding on the diversity of accessions to be included in

391the strategy (Merezhko 1998). One extreme view

392would be to limit the network to the primary gene

393pool—the cultivated species and the closely-related

394species with which they can be readily hybridized. The

395other extreme is that in themodernworld of transgenics

396all biological species are potential genetic resources for

397wheat breeding and the concepts of primary, second-

398ary, and tertiary gene pools are quaint and outmoded. It

399is suggested here, following Merezhko (1998), that we

400should restrict our focus toTriticum species and related

401genera of the Triticeae. This coverage aligns with the

402intention of the International Treaty on Plant Genetic

403Resources for Food and Agriculture (ITPGRFA).

Table 3 Aegilops species and their genomic constitution (After Gill and Friebe 2002 and modified as per chromosome pairingand DNA analysis following Dvorak 1998)

Species Genomic constitution

Nuclear Organellar

Aegilops bicornis (Forssk.) Jaub. & Spach Sb Sb

Aegilops biuncialis Vis. UM (UMo) U

Aegilops markgrafii (Greuter) K. Hammer (known as Aegilops caudata auct non L.) C C

Aegilops columnaris Zhuk. UM (UXco) U2

Aegilops comosa Sm. in Sibth. & Sm. spp. heldreichii (Holzm. ex Boiss.) Eig M M

Aegilops crassa Boiss. Dc1M

c(D

c1Xc) D

2

var. glumiaristata Eig Dc1Dc2M

c(D

c1Dc2Xc) –

Aegilops cylindrica Host DcCc

D

Aegilops geniculata Roth (syn. Ae. ovata auct. non L.) UM (UMo) M

o

Aegilops juvenalis (Thell.) Eig DMU (DcXcUj) D

2

Aegilops kotschyi Boiss. US (US1) S

v

Aegilops longissima Schweinf. & Muschl. S1 S12

Aegilops mutica Boiss. T T,T2

Aegilops neglecta Req. ex Bertol. (syn. Ae. triaristata) UM (UXn) U

var. recta (Zhuk.) Hammer UMN (UXtN) U

Aegilops peregrina (Hack. in J. Fraser) Maire & Weiller (syn. Ae. variabilis) US (US1) Sv

Aegilops searsii Feldman & Kislev ex Hammer Ss Sv

Aegilops sharonensis Eig Ssh S1

Aegilops speltoides Tausch S S,G,G2

Aegilops tauschii Coss. var. tauschii, var. strangulata (Eig) Tzvel. D D

Aegilops triuncialis L. UCt

U,C2

Aegilops umbellulata Zhuk. U U

Aegilops uniaristata Vis. N N

Aegilops vavilovii (Zhuk.) Chennav. DMS (DcXcSv) D

2

Aegilops ventricosa Tausch DvNv

D

Underlined genomes are modified at the polyploidy level; those in brackets were deduced from DNA analysis


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Table 4 The nuclear genome of the perennial species of the tribe Triticeae (after Mujeeb-Kazi and Wang 1995)

Species Genome Species Genome

Agropyron cristatum (L.) Gaertn. PP Leymus angustus (Trin.) Pilger NNNNNNXXXXXX

Agropyron cristatum PPPPPP Leymus arenarius (L.) Hochst. NNNNXXXX

Agropyron desertorum (Fisch. ex Link)

Schult.

PPPP Leymus chinensis (Trin.) Tzvelev NNXX

Agropyron fragile (Roth) P. Candargy PP Leymus cinereus (Scribn. & Merr.) A. Love NNXX

Agropyron michnoi Roshev. PPPP Leymus innovatus (Beal) Pilger NNXX

Agropyron mongolicum Keng PP Leymus mollis (Trin.) Pilger NNXX

Australopyrum pectinatum (Labill.) A. Love WW Leymus racemosus (Lam.) Tzvelev NNNNXXXX

Elymus abolinii (Drobow) Tzvelev SSYY Leymus salinus (M.E. Jones) A. Love NNXX

Elymus alatavicus (Drobow) A. Love SSYYPP Leymus triticoides (Buckl.) Pilger NNXX

Elymus arizonicus (Scribn. & J. G. Sm.)

Gould

SSHH Pascopyrum smithii (Rydb.) A. Love SSHHNNXX

Elymus batalinii (Krasn.) A. Love SSYYPP Psathyrostachys alatavicus NN

Elymus canadensis L. SSHH Psathyrostachys fragilis (Boiss.) Nevski NN

Elymus caninus (L.) L. SSHH Psathyrostachys huachanica Keng NN

Elymus ciliaris (Trin.) Tzvelev SSYY Psathyrostachys junceus (Fisch.) Nevski NN

Elymus dahuricus Turcz. ex Griseb. SSHHYY Psathyrostachys kronenburgii (Hackel) Nevski NN

Elymus drobovii Turcz. ex Griseb. SSHHYY Pseudoroegneria deweyii Jensen, Hatch & Wipff SSPP

Elymus gmelinii (Ledeb.) Tzvelev SSYY Pseudoroegneria tauri (Boiss. & Balansa) A. Love SSPP

Elymus grandiglumis (Keng) A. Love SSYYPP Pseudoroegneria libanotica (Hackel) D. R. Dewey SS, SSSS

Elymus kamoji (Ohwi) S. L. Chen SSHHYY Pseudoroegneria spicata (Pursh) A. Love SS, SSSS

Elymus kengii (Tzvelev) A. Love SSYYPP Pseudoroegneria stipifolia (Czern. ex Nevski) A. Love SS, SSSS

Elymus longearistatus (Boiss.) Tzvelev SSYY Pseudoroegneria strigosa (M.Bieb.) A. Love SS, SSSS

Elymus panormitanus (Parl.) Tzvelev SSYY Secale montanum = Secale strictum (Presl) Presl. RR

Elymus parviglume(Keng) A. Love SSYY Thinopyrum bessarabicum (Savul. & Rayss) A. Love JJ

Elymus pendulinus (Nevski) Tzvelev SSYY Thinopyrum caespitosum C. Koch) Barkw. et

D. R. Dewey

EESS

Elymus shandongensis B. Salomon SSYY Thinopyrum curvifolium (Lange) D. R. Dewey JJJJ

Elymus sibiricus L. SSHH Thinopyrum distichum (Thunb.) A. Love JJEE

Elymus strictus (Keng) A. Love SSYY Thinopyrum elongatum (Host) D. R. Dewey EE

Elymus tsukushiensis Honda SSHHYY Thinopyrum intermedium (Host) Barkworth &

D. R. Dewey

JJJJSS, JJEESS,

EEEESS

Elymus ugamicus Drobow SSYY Thinopyrum junceiforme (A. & D. Love) A. Love JJEE

Elymus vaillantianus (Wulfen ex Schreb.) K.

B. Jensen

SSHH Thinopyrum junceum (L.) A. Love p.p. JJJJEE

Elytrigia repens (L.) Desv. ex B. D. Jackson SSSSHH Thinopyrum nodosum [= Lophopyrum nodosum

(Nevski) A. Love]

EESS

Hordeum bogdanii Wilensky HH to

HHHHHH

Thinopyrum ponticum (Podp.) Z.-W. Liu &

R.-C. Wang

JJJJEEEEEE

Hordeum brevisubulatum Link HH to

HHHHHH

Thinopyrum sartorii (Boiss. & Heldr.) A. Love JJEE

Hordeum iranicum (Bothmer) Tzvelev HH to

HHHHHH

Thinopyrum scirpeum (C.Presl) D. R. Dewey EEEE

Hordeum jubatum L. HH to

HHHHHH

Thinopyrum scythicum EESS

Hordeum violaceum Boiss. & Hohen. HH to

HHHHHH

Thinopyrum turcicum JJJJEEEE


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404 The growing size and sophistication of genetic and

405 molecular stock collections is testimony to their

406 increasing contributions to enable the effective utili-

407 zation of the variation conserved in ‘‘traditional’’

408 germplasm collections. The role of genetic stock

409 collections in the global conservation effort of wheat

410 germplasm should be re-evaluated and these should

411 be given a higher priority in a rationalized system

412 than they had in the past.

413 The Global Wheat, Rye, and Triticale Conservation

414 Strategy (Global Crop Diversity Trust 2007) suggested

415 that the following criteria are essential for an efficient

416 and effective global system for the conservation of

417 wheat genetic resources: globally or regionally-impor-

418 tant, accessible under the internationally agreed terms

419 of access and benefit sharing provided for in the

420 multilateral system as set out in the ITPGRFA,

421 committed to the long-term conservation of the unique

422resources it holds, well-managed and in conformity

423with agreed upon scientific and technical standards of

424management, maintaining effective links to users of

425plant genetic resources, and an indicatedwillingness to

426act in partnership with others to achieve a rational

427system for conserving wheat genetic resources.

428Twenty-three private, national, and global collections

429that fulfilled these criteria where identified as key

430partners for a global wheat conservation network

431(Table 5).

432The proposed wheat conservation strategy focuses

433on the conservation and use of the full spectrum of

434the genetic resources of wheat with the exception of

435the perennial wild relatives. Modern and obsolete

436improved cultivars are generally well-conserved in

437global wheat germplasm collections because many

438such collections either were derived from breeders

439working collections or were primarily established to

Table 5 Collections of a global network of wheat genetic resources

Country Institute No. ofaccessions

Global CIMMYT, El Batan, Mexico 111,681

USA USDA-ARS, National Small Grains Facility, Aberdeen, Idaho 56,218

Russia N.I. Vavilov Research Institute of Plant Industry (VIR), St. Petersburg 39,880

Global ICARDA, Aleppo, Syria 37,830

India National Bureau of Plant Genetic Resources (NBPGR), New Delhi 32,880

Australia Australian Winter Cereals Collection, Tamworth 23,917

France INRA Station d’Amelioration des Plantes, Clermont-Ferrand 15,850

Iran National Genebank of Iran, Genetic Resources Division, Karaj 12,169

Czech Republic Research Institute of Crop Production, Prague 11,018

Ethiopia Plant Genetic Resources Centre, Institute of Biodiversity Conservation and Research, Addis Ababa 10,745

Bulgaria Institute for Plant Genetic Resources ‘‘K. Malkov’’, Sadovo 9,747

Germany Genebank, Institute for Plant Genetics and Crop Plant Research (IPK), Gatersleben 9,633

United Kingdom Department of Applied Genetics, John Innes Centre, Norwich 9,584

Cyprus National Genebank (CYPARI), Agricultural Research Institute, Nicosia 7,696

Japan Genetic Resources Management Section, NIAR (MAFF), Tsukuba 7,148

Switzerland Station Federale de Recherches en Production Vegetale de Changins, Nyon 6,996

Turkey Plant Genetic Resources Department, Aegean Agricultural Research Institute, Izmir 6,381

Netherlands Centre for Genetic Resources, Wageningen 5,529

Canada Plant Gene Resources of Canada, Winnipeg 5,052

USA Wheat Genetics Resource Center, Kansas State University, Manhattan 5,000

Japan Plant Germplasm Institute, Graduate School of Agriculture, Kyoto University 4,378

Spain Centro de Recursos Fitogeneticos, INIA, Madrid 3,183

Sweden Nordic Gene Bank, Alnarp 1,843

Total 23 institutes 434,358

Source: Global Crop Diversity Trust (2007)


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440 service local or regional breeding programs, and

441 these were the accessions most sought by breeders. In

442 fact, many important cultivars are conserved in the

443 majority of national and international collections. The

444 major focus of a global strategy for this category of

445 genetic resource should be to reduce redundancy in

446 the global set of collections to free up resources for

447 other priorities.

448 Landraces have received priority for collection,

449 conservation, and documentation in recent years,

450 supported by the efforts of FAO, the CGIAR, and

451 others because of the increasing threat to their

452 continued existence by the spread of improved

453 modern cultivars. Nevertheless, such cultivars are

454 poorly represented in world collections compared to

455 modern and obsolete cultivars and should remain

456 a priority for the global strategy, both to ensure the

457 collection of material that is not in collections but

458 that still exists in the field and that the long-term

459 conservation of collected material is in line with

460 agreed upon international standards.

461 The wild relatives of wheat are also generally

462 poorly represented in global wheat germplasm col-

463 lections. There are several reasons for this. First, wild

464 relatives are seldom used in conventional breeding

465 programs as compared to cultivars of the same

466 species and usually require an extensive period of

467 germplasm enhancement. Wild species tend to be

468 collected and used by the small number of specialist

469 institutes concerned with interspecific hybridization.

470 Second, they are more difficult to seed increase and

471 maintain because of their tendency to shatter their

472 seed as compared crop cultivars. For this reason also,

473 the distribution and use of some wild species is

474 limited because of their potential as weeds. Finally,

475 wild species, because of their capacity to self-

476 reproduce in nature, have been seen as under less

477 threat of extinction than the cultivated landraces

478 (Global Crop Diversity Trust 2007).

479 Unfortunately, many populations of the annual

480 wild relatives of wheat, particularly those at the

481 extremes of their distribution that are of special

482 interest for breeding purposes, are under threat

483 because of changing patterns of land use and global

484 warming. At the same time, new technologies have

485 made the use of the annual wild relatives as a

486 germplasm source easier, which has generated an

487 interest and need for representative collections of

488 annual wild relatives to be maintained in accessible

489collections. For these reasons the annual wild rela-

490tives should clearly be afforded a greater priority in

491the global wheat germplasm collections than they

492have had in the past. This is not to suggest that all or

493many collections need to move to collect or conserve

494the wild relatives of wheat, but rather, that those with

495the specialized knowledge and capacity to undertake

496the collection and conservation of this category of

497germplasm should be given priority support.

498As noted above, it can also be argued that defined

499genetic stock collections should receive greater

500priority in a balanced global effort to conserve and

501make available for use the genetic resources of wheat.

502Again, because specialists need to develop and

503reliably maintain genetic stocks as true-to-type

504accessions, it is expected that defined genetic stocks

505will be maintained by specialized institutes. The

506emphasis will be to support those institutes to develop

507a coordinated system that replaces the largely ad hoc

508system that has operated to date for the conservation

509of genetic stocks so that valuable material once

510developed and in the public domain is available on a

511continuing basis for all who need it.

512The perennial wild relatives of wheat were not seen

513as a priority for conservation in the collective global

514wheat germplasm system. Again, there are several

515reasons for this. The first, and perhaps most important,

516is that collections of many of these species are

517maintained in perennial grass collections for use in

518breeding programs as grazing species or for other

519uses. Second, despite the number of perennial wild

520relatives of wheat that exist, their extensive global

521spread, and the extensive research that has taken

522place, the number of examples of commercially-

523successful gene transfer from perennial wild relatives

524to wheat remains modest. Third, the perennial wild

525relatives, like their annual counterparts, require spe-

526cialized seed increase knowledge and facilities, which

527is only likely to be available in specialized collections.

528A brief account of wheat breeding at CIMMYT

529and its impact in grain yield

530The global impact of the wheat breeding program of

531CIMMYT has been significant and well-documented

532(Rajaram 1999; Trethowan et al. 2001). Many factors

533have contributed to CIMMYT’s success, such as

534breeding targeted to mega-environments (MEs), use


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535 of a diverse gene pool for crossing, and shuttle

536 breeding (Rajaram et al. 1994; Rajaram 1999; Ortiz

537 et al. 2007a). Another key factor, however, has been

538 the breeding strategies adopted by CIMMYT breed-

539 ers. In this regard, the monitoring of crop trends

540 provides a means for assessing the success of a

541 breeding program.

542 As can be observed in Fig. 2, wheat yields

543 worldwide increased in a linear manner but in recent

544 years the rate of yield increase has slightly declined.

545 Prior to the Green Revolution, the global average

546 wheat yield was increasing at about 1.5% per annum:

547 around 2.2% per annum in developed countries but

548 growing at less than 1% per annum in developing

549 countries. The Green Revolution boosted the growth

550 of average wheat yields to 3.6% per annum in

551 developing countries during 1966–1979. However,

552 yield growth in developing countries slipped to 2.8%

553 per annum during 1980–1994, and then dropped to

554 1.1% per annum during 1995–2005, once again

555 falling below the population growth rate.

556 For international wheat breeding, the period from

557 1951 to date can be divided into well defined

558 improvement eras tracing from the efforts of Borlaug

559 and his colleagues (Ortiz et al. 2007a), which began

560 in the early 1940s, continuing with the efforts of

561 CIMMYT efforts until today and include:

562 • 1951–1962—introduction and farmer-adoption

563 of improved, non-semi-dwarf cultivars with

564enhanced levels of stem (Puccinia graminis f.

565sp. tritici Eriks. & Henn.) and leaf (Puccinia

566triticina Eriks.) rust resistance and better lodging

567tolerance

568• 1962–1975—introduction and farmer adoption of

569semi-dwarf cultivars (it is of interest to note that

570the initial semi-dwarf cultivars like ‘Pitic 62’

571were, in fact, inferior in grain yield, quality and

572even lodging tolerance to the last developed, non-

573semi-dwarfs cultivars like ‘Nainari 60,’ but the

574clear potential advantage of the semi-dwarf

575cultivars was readily apparent to both researchers

576and farmers); and

577• 1975 to date—continued improvement in yield

578potential, host plant resistance (especially combat-

579ing the continual breakdown of leaf rust resistance

580in both bread and durum wheat cultivars, and more

581recently against the stem rust Ug99 strain) and in

582the industrial quality of semi-dwarf cultivars.

583The rate of average wheat yield increases in farmer

584fields in the Yaqui Valley from 1951 to 2005 has

585been impressive (Table 6). Farmers in this valley

586were among the first to grow new cultivars ensuing

587from the work undertaken at the experimental station

588near Ciudad Obregon, where Borlaug started breed-

589ing the wheat lines of the Green Revolution and this

590site is still being used by CIMMYT as its main wheat

591breeding site in Mexico. This trend is representative

592of similar rates of yield increases that have occurred

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

1961 1965 1969 1973 1977 1981 1985 1989 1993 1997 2001 2005

Year

Yie

ld (

kg

/ha

)

FAO World Mean Yld (kg/ha) Yaqui Valley Farmer Mean Yld (kg/ha)

Linear (FAO World Mean Yld (kg/ha)) Linear (Yaqui Valley Farmer Mean Yld (kg/ha))

World Wheat Yield = - 80,785 + 41.77 kg/year; R2 = 0.977

Annual Yield Increase = 2.16%

Yaqui Wheat Yield = - 125,222 + 65.45 kg/year; R2

= 0749

Annual Yield Increase = 1.57%

Fig. 2 Wheat mean grainyields for the World and inthe Yaqui Valley, Sonora,Mexico (1961–2005)(World data source: FAO2007)


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593 in many other wheat production areas such as India,

594 Pakistan, and China, among many others (especially

595 irrigated production regions), notably since the

596 introduction and adoption of semi-dwarf cultivars

597 with resistance to the various rust diseases (Reynolds

598 and Borlaug 2006). Clearly, the tendency has been

599 towards a reduced rate of yield increases over time.

600 This is a fact of considerable concern and is likely not

601 restricted to the Yaqui Valley as shown by the global

602 trends (Fig. 2). It would appear that factors associated

603 with the declining rate of yield increases in wheat

604 include relatively slow increases in private sector

605 investments during the last decade, and lower appli-

606 cations of production inputs as oil prices drove up the

607 cost of fertilizer and pumping irrigation water while,

608 until very recently, the price of wheat gradually fell.

609 In addition, a lack of attention to crop management

610 and the degradation of resources including soil

611 fertility and quality of water for irrigation, combined

612 with an increasing frequency of droughts.

613 Genetic enhancement of spring bread wheat

614 The spring bread wheat germplasm developed at

615 CIMMYT is targeted for its adaptation to diverse

616 wheat production environments in the developing

617 world. The breeding program is based in Mexico and

618 shuttles germplasm between two contrasting environ-

619 ments: Ciudad Obregon (280 N, 32 m.a.s.l.) in

620 northwestern Mexico and Toluca (180 N, 2,640

621 m.a.s.l.) in the highlands of Central Mexico, thereby

622 achieving two generations a year (Braun et al. 1996).

623 This shuttle breeding exposes wheat materials to

624 diverse photoperiod and temperatures and to a range

625 of important diseases. The lines developed through this

626 process are then tested widely around the world and

627selected materials, based on international perfor-

628mance, are identified for continued crossing. There

629are two major breeding thrusts at present: germplasm

630for irrigated areas, and germplasm for rainfed areas.

631Breeding objectives

632Traits of foremost importance in spring wheat

633improvement include: (1) grain yield potential, stabil-

634ity, and wide adaptation, (2) potential for durable

635resistance to diseases such as stem, leaf, and yellow

636(Puccinia striiformis West.) rusts, Septoria tritici

637blotch, Fusarium head blight or scab, and root rots,

638(3) water-use efficiency and water productivity,

639(4) heat tolerance, and (5) end-use quality character-

640istics. Breeding objectives and schemes are

641continually modified to maintain the efficiency and

642effectiveness of germplasm products. For example, as

643water resources continue to decline, wheat will have to

644be produced with less water. This requires the devel-

645opment of high-yielding cultivars that are also efficient

646in water use for irrigated areas or have improved

647performance under drought for rainfed areas. Expan-

648sion of resource-conserving technologies, for example

649zero-tillage in many countries not only reduces

650production costs but also increases long-term sustain-

651ability. However, it is evident that breeding objectives

652must be modified to develop a different kind of

653germplasm that has better emergence and growth

654characteristics and resistance to those diseases and

655pests that survive on residues (Joshi et al. 2007a).

656Yield potential, yield stability, and wide

657adaptation

658The yield potential of semi-dwarf wheat cultivars,

659irrespective of their origin, has continued to increase at

Table 6 Annual rates of increase in average wheat yield in farmer fields in the Yaqui Valley, Sonora, Mexico (1951–2005)

Periods of cultivar development Yield increaseyear-1 (%)

Yield increaseyear-1 (kg ha-1)

Coefficient of determination(year versus yield)

From the first improved non-semi-dwarfs to date 2.36 81 0.857

Improved non-semi-dwarfs 5.20 110 0.808

First generation semi-dwarf cultivars 3.00 111 0.569

Second generation semi-dwarf cultivars 0.15 9 0.011

Further semi-dwarf cultivar development withmodest farmer adoption

-0.43 -23 0.040

Second generation semi-dwarf cultivars to date 0.80 44 0.337


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660 the rate of about 1% annually. Yield stability and wide

661 adaptation are important traits that must be present

662 together with yield potential to ensure that a genotype

663 maintains its superiority in diverse environments,

664 management practices, and biotic and abiotic stresses.

665 Breeding for specific adaptations has not been very

666 successful because in most areas, temperatures and

667 rainfall patterns shift annually. The wide adaptation

668 and stable performance of CIMMYT-derived wheat

669 lines and cultivars are largely due to shuttle breeding

670 in Mexico where segregating populations are selected

671 in two contrasting environments under diverse dis-

672 eases and abiotic stresses, followed by international

673 multi-location testing of advanced lines. This

674 approach is capable of identifying the best stable

675 performers in a single year of testing.

676 Various studies have shown that increases in yield

677 potential are mainly associated with increased bio-

678 mass, kernel number, and harvest index (Sayre et al.

679 1997). Yield components, such as grain size and

680 number, or harvest index in more recent germplasm,

681 have made relatively little or no contribution in

682 explaining the increases in yield potential. This

683 would mean that selection for increased yield

684 potential and higher kernel weight can proceed

685 simultaneously. Large kernel size continues to be

686 an important trait in local markets of various

687 developing countries and appears to be associated

688 with better emergence under poor management.

689 Some of the recent wheat germplasm developed at

690 CIMMYT has not only shown increased grain yield

691 potential but also kernel weight as high as 60 mg in

692 northwestern Mexico, compared with about 40 mg

693 for most of the wheat germplasm developed during

694 the 1980s and 1990s.

695 Although the early increases in yield potential of

696 semi-dwarf wheat cultivars came from the incorpo-

697 ration of dwarfing genes, subsequent progress can be

698 attributed to additive genes. It is likely that intense

699 breeding efforts during the last three decades in the

700 post-Green Revolution era had already selected for

701 larger effect additive genes. If that is the case, then

702 further progress is expected from selecting genes that

703 have much smaller effects, thus making it necessary

704 to modify the commonly used traditional breeding

705 schemes. We began utilizing a single-backcross

706 crossing approach that was initially aimed at incor-

707 porating resistance to rust diseases based on multiple

708 additive, minor genes (Singh and Huerta-Espino

7092004). However, it soon became apparent that the

710single-backcross approach also favored selection of

711genotypes with higher yield potential. The reason

712why single backcross shifts the progeny mean toward

713the higher side is that it favors retaining most of the

714desired additive genes from the backcross or recur-

715rent parent, while simultaneously allowing the

716incorporation and selection of additional useful

717small-effect genes from the donor parent.

718A selected bulk-breeding scheme was introduced

719in bread wheat improvement in the mid-1990s.

720According to Singh et al. (1998b) selection schemes

721have little or no effect on the performance of progeny

722lines, the choice of parents determines the progeny

723response. In all segregating generations until F5 or F6,

724one spike from each of the selected plants is

725harvested as bulk and a sample of seed is used in

726growing the next generation. Individual plants or

727spikes are harvested in the F5 or F6 generation. This

728scheme allows retaining a larger sample of selected

729plants and was found to be highly efficient in terms of

730operational costs. Moreover, retaining a large sample

731of plants in segregating populations increases the

732probability of identifying rare segregates that carry

733most desired genes.

734Introgression of new genetic diversity from unre-

735lated wheat germplasm, including inter-specific

736hybridization, can create a new genetic pool and

737bring in large or small-effect genes that may not be

738present in wheat germplasm commonly used in a

739breeding program. Alien translocation T7DS.7DL-

7407Ae#1L from Thinopyrum elongatum (Host) D.R.

741Dewey that carries leaf and stem rust resistance genes

742Lr19 and Sr25, respectively, has been shown to

743increase yield potential ranging from almost non-

744significant levels to over 15%, depending on genetic

745background under irrigated conditions through

746increased biomass production (Singh et al. 1998a)

747associated with increased spike fertility and photo-

748synthetic rate (Reynolds et al. 2001). Thus, its

749widespread incorporation is underway and we expect

750a quantum jump in yield potential in some of the

751resultant lines.

752Breeding to safeguard wheat crops

753from important diseases

754One or more of the three rust diseases of wheat

755continue to pose major breeding challenges worldwide


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756 due to the pathogens’ ability to evolve continuously, to

757 migrate long distances, and to overcome the deployed

758 race-specific resistance genes. Breeding approaches to

759 control stem rust are described in the below section

760 ‘‘Ug 99 stem rust as a global emerging threat to wheat

761 (food) supply ‘‘ A major genetics and breeding

762 emphasis during the last decades was given to

763 accumulate slow-rusting, minor-resistance genes with

764 additive effects against leaf and yellow-rust patho-

765 gens. High diversity exists in CIMMYT spring wheat

766 lines for such genes and new wheat lines that show

767 negligible disease severity at maturity often carry

768 between four and five slow-rusting resistance genes.

769 Recent studies have found that some of the studied

770 slow-rusting resistance genes have pleiotropic effects

771 on multiple diseases. Most known pleiotropic genes

772 are Lr34/Yr18/Pm38/Bdv1 and Lr46/Yr29/Pm39. Past

773 experience deploying cultivars with slow-rusting

774 resistance has shown that such resistance is durable.

775 CIMMYT initiated breeding for resistance to

776 Septoria tritici blotch, caused by Mycosphaerella

777 graminicola (Fuckel) J. Schrot. (anamorph Septoria

778 tritici)), in semi-dwarf wheat in early 1970 and steady

779 progress has been made since then. Currently, several

780 high-yielding semi-dwarf wheat lines with good

781 resistance are available. Resistance in these wheat

782 genotypes is derived from diverse sources, including

783 re-synthesized wheat lines. Two high rainfall sites

784 (Toluca and Patzcuaro at Michoacan, Mexico), were

785 used for selection. Some re-synthesized wheat lines

786 developed at CIMMYT have shown excellent resis-

787 tance that appears to be leading towards immunity to

788 the disease. These sources offer new genetic diversity

789 of resistance originating from durum wheat or

790 Aegilops tauschii Coss. A high level of resistance

791 from original re-synthesized wheat parents was

792 successfully transferred to derived high-yielding

793 lines.

794 Sources of resistance to scab have been divided

795 into three groups: China and Japan, Argentina and

796 Brazil, and Eastern Europe. More recently, additional

797 sources, including some hexaploid-derived lines from

798 re-synthesized wheat parents have also been identi-

799 fied to carry moderate resistance. Earlier genetic

800 analysis indicated that a few additive genes confer

801 resistance in Chinese and Brazilian wheat lines, and

802 genes present in Chinese sources are different from

803 those in Brazilian sources. Although several genomic

804 regions are now known to contribute quantitative

805resistance (Anderson et al. 2001; Buerstmayr et al.

8062002), a gene from the Chinese cultivar ‘Sumai 3’ in

807the short arm of chromosome 3B has shown the

808largest and most consistent effect in reducing disease

809severity and mycotoxin accumulation (Anderson

810et al. 2001). Further progress in enhancing the level

811of resistance beyond the current level can come from

812a breeding strategy that would favor the accumulation

813of multiple minor genes from various sources into a

814single genotype. CIMMYT is pursuing this strategy at

815present and its outcome will be known in the next

8163–4 years. Some of the recent research advances are

817given below in the section ‘‘Food safety and fighting

818wheat mycotoxins.’’

819Breeding for water-use efficiency and drought

820tolerance

821Wheat is increasingly being grown on marginal lands

822and in farming systems where inputs are limited. In

823most irrigated areas wheat is grown under insufficient

824irrigations. More water-efficient or drought-tolerant

825cultivars can mitigate the effects of changing pro-

826duction environments to some extent. Understanding

827of the genetic basis of drought tolerance is poor.

828Nevertheless, considerable progress has been made in

829yield improvement under drought in recent decades

830using the wheat gene pool and selecting under

831drought stress (Trethowan et al. 2002). The opportu-

832nity exists to improve the tolerance further if new

833genetic variability can be combined with existing

834variability and if the underlying genetic control of

835tolerance can be better understood.

836The re-synthesized wheat lines—developed by

837crossing modern durum wheat with Ae. tauschii, the

838probable donor of the D-genome in hexaploid

839wheat—have introduced new genetic variation into

840the wheat gene pool for many characters. Not

841surprisingly, re-synthesized wheat lines have also

842been a source of variation for drought and heat

843tolerance (Trethowan et al. 2002). Some advanced

844materials derived from re-synthesized wheat lines

845have improved adaptation worldwide, especially in

846drought-stressed environments.

847To improve the breeding efficiency for drought

848tolerance, the CIMMYT strategy is to ensure that

849drought-tolerant germplasm also maintains respon-

850siveness if more moisture becomes available in a

851season. The high yield potential and tolerance to


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852 drought stress are not mutually exclusive and can be

853 bred simultaneously by selecting segregating popu-

854 lations under favorable environments and drought-

855 stress environments in alternate generations—a

856 practice used at CIMMYT. Moreover, to generate a

857 more precise drought stress at different growth

858 stages, a drip-irrigation system has been installed to

859 irrigate 17 ha of an experimental field near Ciudad

860 Obregon, where rainfall during the crop season in

861 most years is negligible. This system allows applica-

862 tion of exact amounts of water at chosen growth

863 stages to generate different drought scenarios repre-

864 senting different parts of the world.

865 Drought tolerance is a complex trait that is also

866 influenced by root diseases. Healthier roots use the

867 available soil moisture more efficiently. Fortunately,

868 resistance to nematodes and some root pathogens is

869 often simply inherited and molecular markers are

870 available to assist selection. CIMMYT uses these

871 markers to incorporate resistance in drought-tolerant

872 wheat materials.

873 Breeding for heat tolerance

874 The genetic control of heat tolerance, like drought

875 tolerance, is poorly understood. Nevertheless, signif-

876 icant variation for heat tolerance exists in the wheat

877 gene pool (Pfeiffer et al. 2005). In many environ-

878 ments, late planting can expose the crop and breeding

879 nurseries to high temperatures from flowering

880 onwards, giving wheat breeders the opportunity to

881 select lines with high levels of heat tolerance. At

882 CIMMYT, lines are selected during the segregating

883 phase for adaptation to heat by planting late. A

884 gravity table is used to separate bulk populations into

885 those that can maintain seed weight under high

886 temperature; the derived lines are then tested under

887 heat stress in yield trials. Physiological tools, such as

888 the infrared thermometer that measures canopy

889 temperature depression (CTD), are also available to

890 assist the plant breeder in discriminating among

891 progenies (Reynolds et al. 1998). Some details on

892 heat screening are also provided in the below section

893 on ‘‘Climate change adaptation and mitigation.’’

894 Heat avoidance or early maturity is an extremely

895 important trait to circumvent effects of high temper-

896 ature at grain filling. All popular cultivars currently

897 grown in the eastern Gangetic Plains are earlier-

898 maturing than cultivars popular in the northwestern

899Gangetic Plains. A simultaneous improvement of

900heat tolerance and yield potential of earlier-maturing

901germplasm is the best option to increase production

902in heat-stress environments and is being practiced

903(Joshi et al. 2007d).

904Breeding for end-use quality

905Bread wheat is generally milled into flour (both

906refined and whole meal) and made into leavened

907breads, flat breads, biscuits, and noodles. The quality

908of proteins, which have a large effect on end-use

909quality, is controlled by known high and low

910molecular weight glutenins and gliadins. A number

911of rapid, indirect quality tests are available that can

912be applied in the early generations to increase the

913probability of identifying progeny with the desired

914quality profiles. Dough rheological properties can be

915measured in different ways; some methods are time-

916consuming but accurate, e.g., the Alveograph, and

917others are faster, less expensive, but slightly less

918accurate, e.g., the Mixograph. Parents for crossing are

919chosen carefully for quality characteristics. Because

920the primary objective of CIMMYT’s breeding pro-

921gram is to enhance yield, quality tests are done in

922advanced generations or after yield testing. A high

923emphasis is being given to improve the leavened and

924flat bread quality characteristics. About a third of

925improved spring wheat materials developed and

926distributed in recent years have excellent to accept-

927able leavened and flat bread making characteristics.

928The section ‘‘Grain quality for adding value in the

929commodity chain’’ provides further details on this

930research area.

931Improving winter/facultative and high-latitude

932wheat

933In the late 1970s and early 1980s CIMMYT research-

934ers realized that winter/facultative wheat breeding for

935the developing world remained largely un-addressed.

936Small efforts to breed facultative wheat during the

937winter cycle in Toluca were primarily based on

938selection from the germplasm introduced from East-

939ern Europe and the USA. However, the winter in

940Toluca was not cold enough for the development of

941competitive lines. The target region for winter/


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942 facultative wheat was in the Central and West Asia

943 region covering 15–20 million ha of the crop in

944 Turkey, Iran, Central Asia, and the Caucasus. The

945 early work in Toluca resulted in the identification of

946 good winter parents and some competitive lines that

947 were used mainly for spring 9 winter crosses with

948 Oregon State University. This germplasm was not

949 sufficiently adapted and neither was it on a scale to

950 provide the winter wheat breeding programs in the

951 target region with competitive material. Thus, CI-

952 MMYT established a winter/facultative wheat

953 breeding program outside of Mexico and directly in

954 the region. Turkey was chosen due to its diversity of

955 environments and because it is a major winter wheat

956 producer in the region. The agreement signed in 1981

957 between the Government of Turkey and CIMMYT

958 anticipated the development of new winter/faculta-

959 tive germplasm through a cooperative breeding

960 program.

961 The newly established program operated through

962 several key research institutions in Turkey: the

963 Central Field Crop Research Institute in Ankara, the

964 Anatolian Agric. Research Institute in Eskisehir, and

965 the Bahri Dagdas International Agric. Research

966 Center in Konya—the latter being established spe-

967 cifically to work on winter wheat breeding. The initial

968 breeding efforts were based on screening the large

969 collection of Turkish, East European, and US culti-

970 vars and making crosses. At the same time,

971 Spring 9 Winter Program operated at Oregon State

972 University (OSU) by Prof. W. Kronstad, supplied

973 F3–F4 populations originating from crosses between

974 Mexican spring wheat lines and winter wheat lines.

975 The lines selected from introduced germplasm in

976 Toluca were also sent to Turkey. All the populations

977 and lines from CIMMYT and OSU, germplasm from

978 Eastern Europe and the USA were screened in Turkey

979 and the best ones selected for distribution through

980 winter/facultative international nurseries. The Tur-

981 key-CIMMYT winter wheat program was joined by

982 ICARDA in 1999 to form the International Winter

983 Wheat Improvement Program (IWWIP). Eventually,

984 Toluca-based winter wheat activities were discontin-

985 ued. The winter/facultative germplasm presently

986 distributed from Turkey combines the germplasm

987 developed by IWWIP through its breeding program

988 in Turkey and Syria as well as new cultivars and

989 breeding lines from all cooperators who are willing to

990 share germplasm. The programs in Eastern Europe,

991the USA, and Central Asia routinely submit the

992germplasm that goes through a selection procedure

993and the best material is included for international

994distribution. This is a specific feature of the winter

995wheat program that is highly appreciated by the

996cooperators. Facultative and Winter Wheat Observa-

997tion Nursery (FAWWON) is distributed globally to

998over 100 cooperators in 50 countries. Additionally,

999yield trials are distributed to the target region of

1000Central and West Asia.

1001In retrospective, the establishment of a winter/

1002facultative breeding program in Turkey was a well-

1003justified move resulting in closing the gap in the

1004provision of germplasm for Central and West Asia.

1005The information on the release of cultivars originat-

1006ing from IWWIP has proved its success in developing

1007germplasm which is well-adapted to the region and

1008competitive with local material. By January 2008, 39

1009cultivars originating from IWWIP had been released

1010in 10 countries of Central and West Asia, including

1011Afghanistan, Iran, and Turkey. Because these culti-

1012vars are competitive in grain yield, they possess

1013higher levels of genetic protection against dominating

1014diseases and especially yellow rust. The genetic

1015diversity of these new cultivars is very broad as their

1016pedigree incorporates not only CIMMYT parents but

1017also a wide range of genetically non-related winter

1018wheat lines from Turkey, Iran, Russia, Ukraine,

1019Romania, Bulgaria, Hungary, and the whole diversity

1020of the US winter wheat.

1021The Turkey-based winter wheat program has now

1022been proven successful both in developing new

1023cultivars as well as in serving as a vehicle for

1024international germplasm exchange and will evolve

1025into a modern program able to efficiently address the

1026upcoming challenges. These are resistance to stem

1027rust, specifically against the Ug99 strain, resistance

1028and tolerance to seed and soil-born pathogens, and

1029bread-making quality, which still needs improve-

1030ment. These will be enhanced through wider

1031application of double haploids and marker-aided

1032breeding. The fundamental difference between winter

1033and spring wheat breeding at CIMMYT is one

1034generation of breeding per year versus two. This

1035should be compensated by the wider use of modern

1036breeding tools, e.g. doubled-haploids.

1037CIMMYT breeding efforts for high latitude spring

1038wheat were initiated in 1999 in order to address one

1039specific challenge: resistance to leaf rust. The vast


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1040 steppe region of northern Kazakhstan and western

1041 Siberia grows around 20 million ha of short season

1042 low input wheat in the environment ranging in

1043 precipitation from 250 to 450 mm. The cultivars

1044 currently grown still represent extensive, tall, and

1045 day-length sensitive type. The average yield ranges

1046 from 1.3 to 1.8 t ha-1. However, even in the years

1047 with sufficient precipitation the response in yield is

1048 limited due to widespread occurrence of leaf rust

1049 (Morgounov et al. 2007). Essentially, all the major

1050 cultivars grown in the region are highly susceptible to

1051 the pathogen. The shuttle breeding program between

1052 Kazakhstan/Siberia and Mexico had its major objec-

1053 tive to incorporate leaf rust resistance while

1054 maintaining the broad adaptability and superior

1055 bread-making quality. Most crosses are made in

1056 Mexico between the Kazakh/Siberian material and

1057 the best Mexican lines which are back- or top crossed

1058 by Kazakh/Siberian or Canadian parents. The result-

1059 ing F2 and F3 are screened under leaf rust pressure in

1060 the area with extended artificial light to allow

1061 selection of day-length sensitive genotypes. The

1062 selected F4 and F5 bulks are sent to two key sites in

1063 Kazakhstan (Astana) and Siberia (Omsk) for selec-

1064 tion under local conditions. The best populations are

1065 then distributed to all the breeding programs in the

1066 region through the Kazakhstan-Siberia Network for

1067 Spring Wheat Improvement (KASIB). By 2008

1068 several batches of germplasm had been sent to the

1069 region. It is obvious that the shuttle program managed

1070 to reach its objective and there are presently lines in

1071 the breeding trials that are competitive in yield while

1072 providing good leaf rust resistance.

1073 The future of CIMMYT breeding for high

1074 latitude regions of Kazakhstan and Siberia may lie

1075 in a gradual transfer of its key activities into the

1076 region. Mexico, by its geographic position, is not a

1077 place to breed for long days. Therefore, special

1078 efforts are needed to extend the day length, which is

1079 expensive and limits the scale of the breeding. Once

1080 the short-term priority of developing the leaf rust

1081 resistance is reached—the program may evolve into

1082 longer-term efforts of improving grain quality and

1083 resistance to Septoria and other pathogens, with

1084 most of its activities based in the region and aligned

1085 with one of the breeding programs. However,

1086 CIMMYT will play a clear role from Mexico, e.g.

1087 making crosses and providing valuable parental

1088 material.

1089Broadening the genetic base of,

1090and re-synthesizing wheat with available wild

1091and landrace genetic resources

1092Interspecific hybrization, embryo rescue, plant regen-

1093eration, cytological diagnostic, breeding methods,

1094stress screening, and the assessment of the stability of

1095the advanced derivatives due to homozygosity, are

1096the tools used by CIMMYT to utilize the wealth of

1097the wheat genetic endowment beyond the cultigen

1098pool (Mujeeb-Kazi and Rajaram 2002). ‘‘Capturing’’

1099wild grass diversity requires more time and effort for

1100a sequential production from F1s, amphiploids and

1101addition lines to translocation lines. Only transloca-

1102tion lines are useful for wheat breeding, but

1103intermediate products (amphiploids and addition

1104lines) are useful to evaluate the presence of useful

1105genes or traits. Also, certain amphiploids may be

1106propagated as new man-made crops, e.g. triticale

1107(9Triticosecale Witmm. ex. A. Camus—an amphi-

1108ploid between wheat and rye).

1109The germplasm sources can be classified into three

1110groups (primary, secondary, and tertiary genepools)

1111according to ease of exchanging genetic material with

1112wheat by meiotic recombinations (Jiang et al. 1994).

1113The primary gene pool is the species that have high

1114frequency rates of recombination with wheat, includ-

1115ing local landraces, wide forms of tetra and hexaploid

1116wheat, as well as diploid species of A and D

1117genomes. The secondary gene pool consists of

1118species that have less homology and reduced recom-

1119bination rates such as S (&B) genome species. The

1120tertiary gene pool consists of alien species that have

1121no recombination with wheat chromosomes under

1122normal conditions. They can be useful because they

1123sometimes possess high levels of host plant resistance

1124to biotic stresses, but the most used sources of genetic

1125enhancement for wheat come mainly from the

1126primary gene pool; for example species containing

1127the A and D genomes are sources of alleles that can

1128recombine directly with their respective genome

1129partners in the cultigen pool.

1130Mujeeb-Kazi et al. (1995) gave details of the early

1131years of research at CIMMYT for utilizing wild grass

1132diversity in wheat improvement through interspecific

1133hybridization. CIMMYT has produced F1 hybrids

1134with many genera in Triticeae including Aegilops,

1135Thinopyrum, Secale, Agropyron Gaertn., Elymus L.,

1136Leymus Hochst., Hordeum L. and Psathyrostachys


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1137 Nevski. Amphiploids involving Aegilops and Thino-

1138 pyrum have been used in wheat improvement and

1139 those of Secale as new sources in triticale breeding

1140 (Mujeeb-Kazi et al. 1995). Addition lines have been

1141 also produced from the above materials. Currently,

1142 this work focuses on producing translocation lines to

1143 supply them to wheat breeders.

1144 CIMMYT has been working on capturing genetic

1145 sources of the D genome of Ae. tauschii via re-syn-

1146 thesizing hexaploid wheat since 1980s, because of the

1147 wide adaptation of the species in many geographical

1148 and climate regions (van Slageren 1994). As indicated

1149 before, the most widely used approach for re-synthe-

1150 sizing hexaploid wheat includes the use of tetraploid

1151 durum and diploid Ae. tauschii. CIMMYT was able to

1152 re-synthesize an excess of 1,000 wheat lines with this

1153 method. These lines have shown significant and useful

1154 diversity that provides better host plant resistance to

1155 biotic stresses and for traits that enhanced adaptation

1156 to abiotic stress-prone environments. Figure 3 shows

1157 the increased recent use by CIMMYT of wild species

1158 genetic endowment in wheat breeding for rainfed

1159 environments through the use of re-synthesized

1160 wheat. The re-synthesized wheat-derived lines extract

1161 more water from deeper soil profiles (Reynolds et al.

1162 2007). Such ability under drought stress may account

1163 for the yield advantage of the re-synthesized wheat

1164 derivatives vis-a-vis their recurrent parents (R. Tre-

1165 thowan, Univ. of Sydney, Australia, personal

1166 communication). The re-synthesized wheat lines were

1167 also used in CIMMYT as new sources to breed host

1168 plant resistance to Karnal bunt (Tilletia indica Mit.)

1169 and Helminthosporium leaf blight (Cochliobolus

1170 sativus (S. Ito & Kurib.) Drechsler ex Dastur)

1171 (Mujeeb-Kazi et al. 2001a, b).

1172 CIMMYT continues exploiting re-synthesized

1173 hexaploid wheat lines following the crossing scheme

1174 shown in Fig. 3 but has also started developing

1175 re-synthesized wheat based on wild tetraploid spe-

1176 cies. A better understanding of wheat evolution

1177 provides for enhancing the ‘‘capture’’ of new diver-

1178 sity through re-synthesis—the first step of an

1179 evolutionary breeding strategy for wheat improve-

1180 ment that broadens the genetic base of the cultigen

1181 pool. In this regard, Warburton et al. (2006) assessed

1182 the change in latent genetic diversity of CIMMYT

1183 released germplasm over time to determine the effect

1184 of selection, and more recent attempts to broaden the

1185 germplasm base of CIMMYT wheat lines. The study

1186used simple sequence repeats (SSR) markers to

1187measure the molecular diversity in CIMMYT and

1188CIMMYT derived-wheat lines over time; to compare

1189this diversity to that of the landraces they replaced;

1190and in particular to assess the effects of newly

1191re-synthesized-derived wheat germplasm on the

1192diversity levels of CIMMYT wheat lines. The data

1193presented by Warburton et al. (2006) for the period

1194from the mid twentieth century to its conclusion,

1195indicate an initial drop in inherent diversity from the

1196level measured in landraces, followed by a period of

1197equilibrium. This is understandable as increasingly

1198diverse bread wheat cultivars from around the world

1199were introduced into the CIMMYT crossing pro-

1200grams, while at the same time fixed lines were

1201selected that required very precise adaptation to

1202specific wheat growing environments around the

1203globe, particularly in developing countries. During

1204this process, the use of host plant resistance mitigated

1205the effects of some diseases, nevertheless new

1206pathogens or biotypes would find a relatively uniform

1207genome in the host crop as a result of earlier

1208narrowing of genetic diversity. However, the use of

1209re-synthesized hexaploid wheat lines in crosses

1210during the past 10 years has dramatically altered the

1211balance of genetic diversity. The inherent diversity of

1212the new re-synthesized derivatives is comparable to

1213that of the landraces; however, they express improved

1214yield, host plant resistance, abiotic stress tolerance

1215and in some cases even better end-use quality.

1216The quest for wheat yield potential

1217It is clear that the periods from 1951 to 1962

1218(adoption of improved non-semi-dwarf cultivars) and

0%

10%

20%

30%

40%

50%

60%

1997

New breeding priority Stem rust priority

2007200620052004200320022001200019991998

Fig. 3 Percentage of crosses with re-synthesized wheat theparental pedigrees in CIMMYT wheat breeding project forrain-fed environments in the last decade


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1219 from 1963 to 1975 (the celebrated period of the

1220 introduction and adoption of reliable semi-dwarf

1221 cultivars) were both eras of remarkable increase in

1222 wheat yields in farmer fields (Table 6). Just as the

1223 impact of the Green Revolution can be attributed

1224 mostly to improved partitioning of the products of

1225 photosynthesis to grain yield, progress in yield of

1226 irrigated wheat since the development of semi-dwarf

1227 lines, as pointed out by Sayre et al. (1997), is also

1228 most strongly associated with improved harvest index

1229 (HI). However, from 1976 to 2005 it was noted a

1230 comparably large decrease in the rate of yield

1231 increase in farmer fields to about 1% year-1, a rather

1232 disturbing observation. There are several reasons,

1233 which are related to both breeding as well as crop

1234 management issues. Previous studies in the Yaqui

1235 Valley have concluded that about 50% of farmer

1236 wheat yield increases have been associated with

1237 genetic improvements in yield potential and 50% has

1238 been associated with improved crop-management

1239 practices, e.g. higher fertilizer rates, better irrigation

1240 management, and the use of bed planting systems

1241 (Bell et al. 1995; Sayre et al. 1997).

1242 The rate of increase in bread and durum wheat

1243 genetic yield potential was high for cultivars bred

1244 from the mid-1960s to the mid-1980s but has subse-

1245 quently declined over the past 10 years. However,

1246 under conditions where pests (rusts in particular) are

1247 not controlled, yield potential for both bread and

1248 durum wheat—bred until the 1990s, showed increases

1249 reflecting the investment made in breeding for

1250 potential durable host plant resistance to rusts. Unlike

1251 the Green Revolution cultivars that relied on single

1252 gene rust resistance—which can easily be eroded as

1253 new pathogen races evolve, more modern cultivars

1254 have multi-gene resistance that can be expected to

1255 stand the test of time (Sayre et al. 1998).

1256 Wheat improvement at CIMMYT expanded the

1257 genetic base of modern wheat lines using conven-

1258 tional breeding as well as cytogenetic-led approaches

1259 for introgressing alleles from wild relatives. For

1260 example, the highly successful ‘Veery’ lines bred in

1261 the early 1980s ensued from the cross of a winter

1262 wheat parent containing the 1B/R rye translocation.

1263 Approximately 3,170 different crosses were made

1264 among 51 individual parents originating in 26

1265 countries around the world to develop the Veery

1266 lines, of which 62 of them were grown annually on

1267 about 3 million ha from Chile to China. These widely

1268adapted Veery lines had an outstanding yield

1269potential and other interesting physiological traits,

1270e.g. the cultivar ‘Seri 82’showed superior leaf

1271photosynthetic rate, stomatal conductance, and leaf

1272greenness relative to a set of hallmark varieties

1273developed both before and after its release (Fischer

1274et al. 1998). The success of lines possessing the

1275chromosome substitution T1BL.1RS may also be

1276related to increased tolerance to stresses (Villarreal

1277et al. 1997). Last but not least, the use of

1278winter 9 spring crosses for wheat improvement at

1279CIMMYT, which began in the early 1970s, contrib-

1280uted to increasing the genetic diversity of the spring

1281wheat gene pool.

1282CIMMYT ideotype research using modem semi-

1283dwarf spring wheat cultivars, representing a range of

1284yield potential, supports the idea that genes confer-

1285ring yield, through improved adaptation to the crop

1286environment, are associated with a less competitive

1287phenotype (Reynolds et al. 1994a). One important

1288implication of these results is that improvement in

1289yield potential would appear to be more a function of

1290improved adaptation to canopy microenvironment,

1291rather than macro-environmental factors such as

1292climate. Reynolds et al. (1999) reviewed the physi-

1293ological and genetic changes in irrigated wheat in the

1294post-Green Revolution period. Their assessment

1295shows that morphological traits associated with

1296increased yield potential in CIMMYT-derived wheat

1297cultivars released between 1962 and 1988 include

1298grain number and HI (Reynolds et al. 1999).

1299Although increased HI seems to account for improve-

1300ments in genetic yield potential, even in the aftermath

1301of the Green Revolution, it should be taken into

1302account with caution due to theoretical limit to HI,

1303estimated at 60% (Austin et al. 1980), e.g. if HI could

1304be raised to 60% from its current maximum value

1305(approximately 50%), it implies that grain yields

1306could only be increased by a further 20% using HI as

1307a selection criterion, unless total crop biomass is also

1308raised.

1309As indicated previously, significant increase in

1310yield and biomass has been observed in several

1311backgrounds when alien chromatin associated with

1312Lr19 was introgressed from Th. elongatum (Reynolds

1313et al. 2001). Lr19—transferred to wheat through

1314the 7DL.7Ag translocation—was associated with

1315increases in yield (average 13%), final biomass

1316(10%), and grain number (15%) in all backgrounds


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1317 studied. Lrl9 was associated with an increased

1318 partitioning of biomass to spike growth at anthesis

1319 (13%), a higher grain number per spike, higher

1320 radiation-use efficiency and flag-leaf photosynthetic

1321 rate during grain filling (Reynolds et al. 2005).

1322 The hypothesis that photosynthesis and RUE may

1323 respond directly to a larger number of grains per

1324 spike was tested experimentally by imposing a light

1325 treatment during boot stage. The treatment was

1326 associated with a small increase (5%) in the propor-

1327 tion of biomass invested in spike mass at anthesis,

1328 reflected by on average three extra grains per spike at

1329 maturity. The treatment was associated with 25%

1330 more yield and 22% more biomass than checks, while

1331 carbon assimilation rate measured on flag-leaves

1332 during grain-filling was 10% higher than checks. The

1333 results suggest that RUE can be increased indirectly

1334 by increasing sink strength and a major yield-limiting

1335 factor in modern high-yielding spring wheat is still

1336 the determination of kernel number (Reynolds et al.

1337 2005). This research illustrates the advantage of

1338 introgressing wild relatives’ genes for improving

1339 grain yield potential in wheat.

1340 The power of in silico breeding to define wheat

1341 genetic enhancement approaches

1342 The strategies used by CIMMYT breeders have

1343 evolved. Pedigree selection was used primarily from

1344 1944 until 1985. From 1985 until the second half of

1345 the 1990s the main selection method was a modified

1346 pedigree/bulk method (MODPED) (van Ginkel et al.

1347 2002), which successfully produced many of the

1348 widely adapted wheat cultivars now being grown in

1349 the developing world. This method was replaced in

1350 the late 1990s by the selected bulk method (SEL-

1351 BLK) (van Ginkel et al. 2002) in an attempt to

1352 improve resource-use efficiency. The major differ-

1353 ences between MODPED and SELBLK are outlined

1354 below.

1355 The MODPED method begins with pedigree

1356 selection of individual plants in the F2 generation

1357 followed by three bulk selections from F3 to F5, and

1358 pedigree selection in the F6; hence the name modified

1359 pedigree/bulk. In the SELBLK method, spikes of

1360 selected F2 plants within one cross are harvested in

1361 bulk and threshed together, resulting in one F3 seed

1362 lot per cross. This selected bulk selection is also used

1363from F3 to F5, while pedigree selection is used only in

1364the F6. A major advantage of SELBLK compared

1365with MODPED is that fewer seed lots need to be

1366harvested, threshed, and visually selected for seed

1367appearance. In addition, significant savings in time,

1368labor, and costs associated with nursery preparation,

1369planting, and plot labeling ensue, and potential

1370sources of error are avoided (van Ginkel et al. 2002).

1371Although some small-scale field experiments have

1372been conducted comparing the efficiencies of CI-

1373MMYT wheat breeding methods (Singh et al. 1998b),

1374the efficiency of SELBLK, compared with that of

1375MODPED, remained untested on a larger scale until

1376the use of the breeding simulation tool of QuLine.

1377The breeding and simulation tool of quLine

1378QU-GENE is a simulation platform for quantitative

1379analysis of genetic models, which consists of a two-

1380stage architecture (Podlich and Cooper 1998). The

1381first stage is the engine (referred to as QUGENE), and

1382its role is to define the genotype 9 environment (GE)

1383system (i.e., all the genetic and environmental

1384information of the simulation experiment), and

1385generate the starting population of individuals (base

1386germplasm). The second stage encompasses the

1387application modules, whose role is to investigate,

1388analyze, or manipulate the starting population of

1389individuals within the GE system defined by the

1390engine. The application module will usually represent

1391the operation of a breeding program. A QU-GENE

1392strategic application module, QuLine, has therefore

1393been developed to simulate the breeding procedure

1394for deriving inbred lines. Built on QU-GENE,

1395QuLine (previously called QuCim) is a genetics and

1396breeding simulation tool that can integrate various

1397genes with multiple alleles operating within epistatic

1398networks and differentially interacting with the

1399environment interaction, and predict the outcomes

1400from a specific cross following the application of a

1401real selection scheme (Wang et al. 2003; Wang et al.

14022004). It therefore has the potential to provide a

1403bridge between the vast amount of biological data

1404and breeders’ queries on optimizing selection gain

1405and efficiency. QuLine has been used to compare two

1406selection strategies (Wang et al. 2003), to study the

1407effects on selection of dominance and epistasis

1408(Wang et al. 2004), to predict cross performance

1409using known gene information (Wang et al. 2005),


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https://www.researchgate.net/publication/226265694_Comparison_of_two_crossing_and_four_selection_schemes_for_yield_yield_traits_and_slow_rusting_resistance_to_leaf_rust_in_wheat_Reprinted_from_Wheat_Prospects_for_global_improvement_1998?el=1_x_8&enrichId=rgreq-b97bd0b2e59dcb0078850802c561253d-XXX&enrichSource=Y292ZXJQYWdlOzIyNTgyMDgyMztBUzoxMDQxNTU1MzY0MjkwNzFAMTQwMTg0NDAyMzQ3Nw==

https://www.researchgate.net/publication/230249308_Sink-limitation_to_yield_and_biomass_A_summary_of_some_investigations_in_spring_wheat?el=1_x_8&enrichId=rgreq-b97bd0b2e59dcb0078850802c561253d-XXX&enrichSource=Y292ZXJQYWdlOzIyNTgyMDgyMztBUzoxMDQxNTU1MzY0MjkwNzFAMTQwMTg0NDAyMzQ3Nw==


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1410 and to optimize marker-assisted selection to efficient

1411 pyramid multiple genes (Kuchel et al. 2005; Wang

1412 et al. 2007a, b; Ye et al. 2007).

1413 Comparison of breeding efficiencies for different

1414 selection strategies through simulation

1415 The genetic models developed have accounted for

1416 epistasis, pleiotropy, and genotype-by-environment

1417 interaction. The simulation experiment comprised the

1418 same 1,000 crosses, developed from 200 parents, for

1419 both breeding strategies. A total of 258 advanced

1420 lines remained following 10 generations of selection.

1421 The two strategies were each applied 500 times on 12

1422 GE systems.

1423 Genetic gain in yield from MODPED and SELBLK

1424 The average adjusted gains were 6.7 t ha-1 for no

1425 epistasis, 5.4 t ha-1 for di-genic epistasis, and

1426 5.7 t ha-1 for tri-genic epistasis, which indicates that

1427 epistasis will reduce the adjusted gain. The adjusted

1428 gain associated with the absence of pleiotropy is also

1429 higher than that for the presence of pleiotropy. These

1430 results suggest that the increase in gene number and

1431 the presence of epistasis and pleiotropy make it more

1432 difficult for a breeding strategy to identify the trait

1433 performance level of the best genotype in the defined

1434 GE system. When the experimental factors are

1435 considered individually, the adjusted gain from

1436 SELBLK is always significantly higher than that

1437 from MODPED, except in the absence of pleiotropy,

1438 indicating SELBLK is at least equivalent to or better

1439 than MODPED.

1440 The average adjusted genetic gain on yield is

1441 5.8 t ha-1 for MODPED and 6 t ha-1 for SELBLK, a

1442 difference of 3.3% (Fig. 4a). This difference is not

1443 large and therefore unlikely to be detected using field

1444 experiments (Singh et al. 1998b). However, it can be

1445 detected through simulation, which indicates that the

1446 high level of replication (50 models by 10 runs in this

1447 experiment) possible using simulations can better

1448 account for the stochastic properties of a run of a

1449 breeding strategy and for the sources of experimental

1450 errors. The average adjusted gains for the two yield

1451 gene numbers 20 and 40 are 6.83 and 5.02, respec-

1452 tively, suggesting that genetic gain decreases with

1453 increasing yield gene number.

1454Number of crosses remaining after selection

1455The same 1,000 crosses were made for both breeding

1456strategies and 258 advanced lines were selected after

1457a breeding cycle, regardless of the GE system used.

1458The number of crosses remaining after one breeding

1459cycle is significantly different among models and

1460strategies, but not among runs. The number of crosses

1461remaining from SELBLK is always higher than that

1462from MODPED, which means that delaying pedigree

1463selection favors diversity. On average, 30 more

1464crosses were maintained in SELBLK (Fig. 4b).

1465However, there is a crossover between the two

1466breeding strategies (Fig. 4b). Prior to F5 the number

1467of crosses in MODPED is higher than that in

1468SELBLK. The number of crosses becomes smaller

1469in MODPED after F5 when pedigree selection is

1470applied in F6. Among-family selection from F1 to F51471in SELBLK is equal to among-cross selection, and

1472results in a greater reduction in cross number for

1473SELBLK compared to MODPED in the early gener-

1474ations. In general, only a small proportion of crosses

1475remain at the end of a breeding cycle (11.8% for

1476MODPED and 14.8% for SELBLK); therefore,

1477intense among-cross selection in early generations

1478is unlikely to reduce the genetic gain. On the

1479contrary, breeders will tend to concentrate on fewer

1480but ‘‘higher-probability’’ crosses. That just a few

1481crosses of the many generated remain after the final

1482yield trial stage is common in most breeding

1483programs. Since more crosses remain in SELBLK,

1484the population following selection from SELBLK

1485may have larger genetic diversity than that from

1486MODPED. In this context, SELBLK is also superior

1487to MODPED.

1488Resource allocation

1489Since the number of families and selection methods

1490after F8 are basically the same for both MODPED and

1491SELBLK, only the resources allocated from F1 to F81492are compared. The total number of individual plants

1493from F1 to F8 was calculated to be 5,155,090 for

1494MODPED and 3,358,255 for SELBLK (Fig. 4c).

1495Assuming that planting intensity is similar, SELBLK

1496will use approximately two thirds of the land

1497allocated to MODPED. Furthermore, SELBLK pro-

1498duces a smaller number of families compared to

1499MODPED (Fig. 4d). From F1 to F8, there are 63,188


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1500 families for MODPED but only 24,260 for SELBLK,

1501 approximately 40% of the number for MODPED.

1502 Therefore when SELBLK is used, fewer seed lots

1503 need to be handled at both harvest and sowing,

1504 resulting in significant savings in time, labor, and

1505 cost.

1506 Further use of in silico-aided genetic

1507 enhancement

1508 QuLine is a QU-GENE application module that was

1509 specifically developed to simulate CIMMYT’s wheat

1510 breeding programs, but with the potential to simulate

1511 most, if not all, breeding programs for developing

1512 inbred lines. The breeding methods that can be

1513 simulated in QuLine include mass selection, pedigree

1514 breeding (including single seed descent), bulk pop-

1515 ulation breeding, backcross breeding, top cross (or

1516 three-way cross) breeding, doubled haploid breeding,

1517marker-assisted selection, and combinations and

1518modifications of these methods. The chromosomal

1519locations of genes and markers, and their occurrence

1520in specific parents can be explicitly and precisely

1521defined (Wang et al. 2003). Simulation experiments

1522can therefore be designed to compare the breeding

1523efficiencies of different selection strategies under a

1524series of pre-determined genetic models.

1525A great amount of studies on quantitative trait loci

1526(QTL) mapping have been conducted for various

1527traits in plants and animals in the last 10 years

1528(Dwivedi et al. 2007 and references therein). How-

1529ever, QTL discovery and cultivar development in

1530most cases are two separate processes. How QTL

1531mapping results can be used to pyramid desired

1532alleles at various loci has rarely been addressed in the

1533literature. As the number of published genes and QTL

1534for various traits continues to increase, the challenge

1535for plant breeders is to determine how to best utilize

A

50

51

52

53

54

55

56

57

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200

300

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600

700

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F2

F3

F4

F5

F6

F7

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F8(S

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F9(T

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25

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35

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F9(T

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R

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R)

Filial generation

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1.5

2.0

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F2

F3

F4

F5

F6

F7

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F8(Y

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F8(S

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Fig. 4 Results from the simulation experiment (adapted withmodifications from Fig. 2 of Wang et al. (2003)). (a) Adjustedgenetic gain after one breeding cycle across all experimentalsets; (b) Number of crosses after each generation’s selectionacross all experimental sets; (c) Number of individual plants ineach generation in one breeding cycle; (d) Number of familiesin each generation in one breeding cycle. F8(T), F8 field test in

Toluca; F8 (B), F8 field test in El Batan; F8 (YT), F8 yield trialin Ciudad Obregon; F8(SP), F8 small plot evaluation in CiudadObregon; F9(T), F9 field test in Toluca; F9(B), F9 field test inEl Batan; F9(YT), F9 yield trial in Ciudad Obregon; F9(SP), F9small plot evaluation in Ciudad Obregon; F10(YR), F10 striperust screening in Toluca; F10(LR), F10 leaf rust screening in ElBatan


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1536 this multitude of information in the improvement of

1537 crop performance. QuLine provide an appropriate

1538 tool that can combine different types and levels of

1539 biological data such that the complex and voluminous

1540 data is turned into knowledge that can be applied in

1541 breeding.

1542 Information management and knowledge sharing:

1543 the wheat phenome atlas

1544 A useful new tool for crop genetic improvement is

1545 association analysis (AA), which is the direct selec-

1546 tion of polymorphic markers associated with

1547 phenotypic variation for important traits and identi-

1548 fied by the linkage disequilibrium (LD) between loci

1549 (Thornsberry et al. 2001; Flint-Garcia et al. 2003).

1550 This LD is determined by their physical distance

1551 across chromosomes and has proven to be useful for

1552 dissecting complex traits because it offers a fine scale

1553 mapping due to historical recombination (Lynch and

1554 Walsh 1998). However, covariance between markers

1555 and traits not due to physical distance can arise due to

1556 population structure caused by admixture, mating

1557 system, and genetic drift, or by artificial or natural

1558 selection during evolution, domestication, or plant

1559 improvement. These factors create subpopulation

1560 structure in a linkage disequilibrium study, which

1561 leads to LD between loci that are not physically

1562 linked and cause a high rate of false positives when

1563 relating polymorphic marker to phenotypic trait

1564 variation. However, LD due to physical linkage can

1565 be differentiated from LD due to population structure

1566 using statistical methods such as those suggested by

1567 Pritchard et al. (2000) and Yu et al. (2006). In

1568 addition to controlling population structure, success-

1569 ful application of AA requires comprehensive

1570 phenotypic data, including replicated field trials for

1571 modeling GE interaction. An advantage of AA is that

1572 large amounts of historical phenotypic data can be

1573 used, as demonstrated by Crossa et al. (2007). This

1574 can decrease the need for additional, expensive and

1575 time consuming phenotyping.

1576 CIMMYT, Cornell Univ (Ithaca, NY, USA), and

1577 the Univ. of Queensland (Brisbane, Australia)

1578 recently launched the Wheat Phenome Atlas initiative

1579 which aims for enabling technologies to link geno-

1580 type to phenotype across a wide range of agronomic

1581 traits of high priority to wheat farmers across the

1582world. The Wheat Phenome Atlas will facilitate more

1583rapid development of molecular breeding tools,

1584increased understanding of genotype-by-environment

1585interaction, and will lead to increased precision and

1586scope of targeted breeding impacts. The Phenome

1587Atlas Toolbox will be developed as an open source

1588resource for wheat genetics, breeding, pathology,

1589physiology, and biological research. The initiative is

1590based on a unique database (amongst crop plants)

1591developed by CIMMYT and national partners over

1592the past half century, based on the field evaluation of

1593more than 15,000 elite breeding lines in more than

1594100 locations across the world—at a cost of about

1595US$ 0.5 billion. All seed from these breeding lines

1596has been preserved in the CIMMYT germplasm bank

1597and can now be subjected to whole genome

1598genotyping.

1599The proof-of-concept in this area was recently

1600carried out by researchers from the CIMMYT Crop

1601Research Informatics Laboratory (an initiative of the

1602CIMMYT-IRRI Alliance), the University of Queens-

1603land, and Cornell University with the biotech

1604company Triticarte, who have developed the high

1605throughput genotyping protocol—diversity array

1606technology or DArT for short (Crossa et al. 2007).

1607The Wheat Phenome Atlas initiative is based around

1608the ICIS (International Crop Information System), an

1609open-source informatics platform used by CGIAR,

1610NARS, and private sector germplasm banks,

1611researchers, and breeders across the world. All data

1612and resources developed through this initiative will

1613be available to wheat researchers and breeders across

1614the world through public access databases and

1615portals. It is envisaged that additional international

1616collaborators will join the initiative, including

1617advanced research institutes from the USA, Europe,

1618and Australasia, strong NARS from Latin America

1619and Asia, plus private sector breeding companies

1620from across the world.

1621Establishing the analytical tools to deal with data

1622sets of over 15,000 lines 9 40 years 9 80

1623traits 9 100 locations 9 2,000 DNA data points

1624(approximately 10 billion data points) will involve

1625the development of new and powerful bioinformatics

1626tools and webpage visualization software. The

1627Phenome Atlas Toolbox will facilitate the identifica-

1628tion of gene blocks having beneficial effects on high

1629priority agronomic traits such as rust resistance,

1630drought tolerance, and yield. From these outputs it


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1631 will be possible to develop molecular tools for

1632 rapidly introgressing these elite gene blocks into

1633 new cultivars. The Wheat Phenome Atlas database

1634 will also be used for modeling and simulation studies

1635 to predict cultivar performance in a range of global

1636 environments, including future environments pre-

1637 dicted by climate change models (CIMMYT 2007). It

1638 is envisaged that the Phenome Atlas Toolbox will

1639 develop dynamically with input from wheat research-

1640 ers worldwide. The Phenome Atlas Toolbox will be

1641 generic and applicable to all biological systems,

1642 whether plant or animal.

1643 Safe and legal movement of wheat germplasm

1644 worldwide

1645 CIMMYT has a global mandate for the improvement

1646 of wheat and maize and it has also the responsibility

1647 of conserving the germplasm of these crops.

1648 CIMMYT’s germplasm improvement programs rely

1649 heavily on the free international exchange of maize

1650 and wheat seed. All concerned institutions, cooper-

1651 ators, and regulating authorities must have confidence

1652 in the safety of both imported and exported seed to

1653 facilitate such exchange. CIMMYT is fully commit-

1654 ted to maintaining fundamental health standards in its

1655 worldwide operations. These standards are dictated at

1656 different levels by the International Plant Protection

1657 Convention (FAO 1997 https://www.ippc.int/IPP/En/

1658 default.jsp), by IT-PGRFA (FAO 2002), and by the

1659 CGIAR (1999).

1660 CIMMYTpolicies and practices and its SeedHealth

1661 Laboratory (SHL) control and ensure the implemen-

1662 tation of international and national phytosanitary

1663 regulations for material that is distributed every year.

1664 CIMMYT SHL has operated since 1998 under the

1665 approval of the Mexican Ministry of Agriculture

1666 (SAGARPA) (Norma Oficial Mexicana 036-FITO-

1667 1995), and since April 2007 with the accreditation

1668 under norm ISO/IEC NMX-EC-17025-IMNC-2005

1669 General Requirements for the Competence of Testing

1670 and Calibration Laboratories. These essential legal

1671 recognitions guarantee to the Mexican phytosanitary

1672 authorities that CIMMYT seed exchange activities do

1673 not jeopardize the internal Mexican or international

1674 phytosanitary situation and that the quarantine proce-

1675 dure carried out on seed introductions strictly adheres

1676 to Mexican phytosanitary regulations. Likewise, they

1677reassure our collaborators that CIMMYT procedures

1678are standardized, internationally recognized, and con-

1679trolled constantly through internal and external audit

1680processes.

1681The principal functions of CIMMYT SHL are to:

1682certify the viability and health of maize and small

1683grain cereal seed for international shipments, con-

1684trol the safety of seed arriving to CIMMYT and

1685apply Mexican quarantine regulations, detect the

1686unintentional presence of transgenes on maize

1687introductions from risky countries, maintain the

1688relationship with, and act as spokesman with

1689Mexican phytosanitary authorities, supervise the

1690seed-treating procedures, inspect field multiplication

1691and introduction plots, and ensure that chemical

1692prophylaxes against quarantine disease are applied

1693in the multiplication plots, in storehouses, and in

1694seed preparation areas. The SHL represents the

1695point of entry and exit of all seed shipments to and

1696from CIMMYT headquarters.

1697Seed samples are delivered by programs for

1698analyses or are received from collaborators; upon

1699completion of the testing process the seed is

1700‘‘released’’ and ready to be shipped abroad or planted

1701in CIMMYT experimental stations. According to

1702Mexican phytosanitary regulations, when the inter-

1703ception of a pathogen of quarantine importance

1704occurs both on outgoing or incoming material, the

1705SHL must inform Mexican phytosanitary authorities,

1706who will indicate the measures to follow to prevent

1707the spread of the pathogen.

1708During 2007 the SHL carried out quarantine

1709procedures on 62 seed introductions of small grain

1710cereals (wheat, triticale, and barley) proceeding from

171120 countries and analyzed 822 samples. From this

1712number of samples, which included 41,257 seeds, two

1713interceptions of the quarantined pathogen Tilletia

1714indica were made on two seed introductions that were

1715incinerated.

1716Karnal bunt is considered a disease of moderate

1717economic importance (CABI 2005), for example in

1718Mexico, where Karnal bunt appears regularly, direct

1719losses are not very significant and do not exceed 1%.

1720However, the indirect costs to the Mexican economy

1721are more significant due to quarantine measures,

1722which have to be applied for grain exports (Brennan

1723et al. 1992). The same happens in the USA (Rush

1724et al. 2005). In Europe and Australia the disease is

1725still considered a high risk (Bartlett 2000; Murray and


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1726 Brennan 1998), in spite of the strict environmental

1727 requirement that the pathogen has for developing and

1728 affecting wheat and triticale (Jones 2007). The

1729 disease is given political recognition in many coun-

1730 tries. In terms of its phytosanitary importance, the

1731 pathogen is quarantined in more then 40 countries in

1732 the world (Rush et al. 2005). Hence, CIMMYT is

1733 obligated to devote a considerable amount of

1734 resources in applying a zero-tolerance policy against

1735 this disease. Besides T. indica, particular care is also

1736 taken by CIMMYT to prevent infections by Xantho-

1737 manas translucens (Jones et al.) Vauterin et al. pv.

1738 undulosa, the Barley Stripe Mosaic virus, and the

1739 Wheat Streak Mosaic virus through inspection of the

1740 seed before and after planting.

1741 In the case of outgoing germplasm, 2,468 samples

1742 were tested at the SHL before the shipments were

1743 sent in 2007. The phytosanitary quality of outgoing

1744 seed is particularly high due to the procedure

1745 followed in the multiplication plots that are planted

1746 in an internationally recognized Karnal bunt free area

1747 in northwest Mexico and that are submitted to a

1748 prophylaxis against Karnal bunt and other foliar

1749 diseases, which includes 3–4 fungicide treatments

1750 with propiconazole and tebuconazole during the

1751 cropping cycle and insecticide to protect the crop

1752 from aphid- and mite-borne viruses. Therefore, the

1753 range of pathogens detected on the seed mainly

1754 consists of saprophytes or minor seed-borne patho-

1755 gens that do not affect seed quality, such as fungi

1756belonging to the genus Alternaria, Cephalosporium,

1757Fusarium, Bipolaris, Curvularia, and Cladosporium.

1758Starting 1 January 2007, the CGIAR Centers had

1759to use the Standard Material Transfer Agreement

1760(SMTA) for all shipments, which was adopted in

1761the first session of the Governing Body of the

1762IT-PGFRA. It was agreed upon through the Statement

1763of the CGIAR Centers regarding Implementation of

1764the Agreements between the Centers and the govern-

1765ing body of the International Treaty on Plant Genetic

1766Resources for Food and Agriculture. CIMMYT

1767started using the SMTA as of 14 January 2007, but

1768did not distribute any material prior to that date.

1769During 2007, 565 shipments were sent under the

1770SMTA and three were rejected.

1771Table 7 provides a summary of the number of

1772international nursery seed sets sent during 2007 from

1773CIMMYT headquarters. This table includes bread,

1774durum wheat, triticale, and barley. The seed is

1775distributed mainly to governmental research institu-

1776tions and national programs in Asia and Central and

1777West Asia and Northern Africa (CWANA) through

1778the CIMMYT International Wheat and Improvement

1779Network that every year makes available 14 nurseries

1780adapted to different environments. Table 8 provides a

1781list of nurseries available and whose seeds can be

1782requested by any party that agrees with the SMTA

1783which regulates the use and benefit sharing of the

1784germplasm according to the IT-PGRFA. This activity

1785constitutes the backbone of the breeders’ research

Table 7 Number of international nurseries sets of small grain cereals (wheat, barley and triticale) sent by CIMMYT during 2007to different regions

2007

Region Barley Bread wheat Durum wheat Special nurseries Triticale Total by region

Africa 24 85 10 1 12 132

Asia 47 205 41 16 309

Caribbean 2 2

CWANAa 133 325 123 52 633

Europe 19 110 46 30 205

North America 21 113 27 1 19 181

Oceania 1 2 1 4

South America 30 119 27 3 28 207

Total by crop 277 957 276 5 158 1,673

a CWANA: Central/West Asia and North Africa, which include Algeria, Egypt, Ethiopia, Eritrea, Libya, Mauritania, Morocco,Sudan and Tunisia (North Africa and Nile Valley), Bahrain Iraq, Jordan, Kuwait, Lebanon, Palestine, Qatar, Saudi Arabia, theSultanate of Oman, Syria, Turkey, the United Arab Emirates and Yemen (Middle East), Afghanistan, Armenia, Azerbaijan, Georgia,Iran, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan (Central Asia and Caucasus)


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1786 programs due to the valuable information sent back by

1787 the collaborators that feeds into the breeding program.

1788 Such feedback allows for a constant and prompt

1789 improvement of wheat germplasm according to the

1790 users’ needs and to the biotic and abiotic stresses that

1791 threaten wheat production in developing countries.

1792 CIMMYT also distributes a great number of lines

1793 that are developed under specific projects between

1794 CIMMYT and several collaborators in the public

1795 and private sector. These are called miscellaneous

1796 shipments and as it is shown in Table 9 the greatest

1797 part is sent to Africa, Asia, and North America.

1798 Miscellaneous shipments include also germplasm

1799requested by genebanks to absolve specific scientific

1800needs and also for conservation of duplicates in other

1801genebanks.

1802International CIMMYT wheat nursery systems

1803CIMMYT-improved germplasm is dispatched through

1804nurseries targeted to specific spring and winter type,

1805irrigated, high-rainfall, semi-arid, and heat-tolerant

1806requiring agro-ecological environments to a network of

1807wheat researchers worldwide (http://www.cimmyt.org/

1808english/wps/obtain_seed/frmrequesttrialswheat.htm).

Table 8 Name of thenurseries distributed fromMexico by CIMMYT everyyear to the InternationalWheat ImprovementNetwork

a ICARDA-CIMMYTBarley program, distributedonly until 2007

Name of the nursery Crop

Elite Spring Wheat Yield Trial Spring bread wheat

Semi-Arid Wheat Yield Trial Spring bread wheat

High-Rainfall Wheat Yield Trial Spring bread wheat

International Bread Wheat Screening Nursery Spring bread wheat

Semi-Arid Wheat Screening Nursery Spring bread wheat

High-Rainfall Wheat Screening Nursery Spring bread wheat

High-Latitude Wheat Screening Nursery Spring bread wheat

(Fusarium) Scab Resistance Screening Nursery Spring bread wheat

Stem Rust Resistance Screening Nursery Bread wheat

International Durum Yield Nursery Durum wheat

International Durum Screening Nursery Durum wheat

International Triticale Yield Nursery Triticale

International Triticale Screening Nursery Triticale

International Barley Yield Trial z Barley

International Barley Observation Nurserya Barley

Early Maturity Barley Screening Nurserya Barley

Hull-less Barley Screening Nurserya Barley

Table 9 Number of small grain cereals lines distributed as miscellaneous shipment during 2007 to different regions in the world

Region Bread wheat Durum wheat Triticale Barley Genebank Total by region

Africa 12,138 4,953 430 415 132 18,068

Asia 8,548 503 198 304 717 10,270

Caribbean 6 3 1 10

Europe 672 984 47 21 716 2,440

Middle Easta 1,485 52 27 61 1,238 2,863

North America 1,766 13 12 1,460 17,735 20,986

Oceania 3,267 546 33 1 28 3,875

South America 5,006 6 28 2,679 1,185 8,924

Total by crop 32,888 7,080 775 4,942 21,751 67,436

a Bahrain, Iraq, Jordan, Kuwait, Lebanon, Palestine, Qatar, Saudi Arabia, the Sultanate of Oman, Syria, Turkey, the United ArabEmirates and Yemen


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1809 In exchange, they provide the data from their trials to

1810 CIMMYT for further cataloging and analysis. The use

1811 of the international trial data assists in the improve-

1812 ment of wheat breeding approaches by CIMMYT. For

1813 example, this information has proven useful for

1814 establishing associations among stress environments

1815 and irrigation systems in the screening fields at

1816 CIMMYT’s main wheat breeding sites in Mexico

1817 (Ciudad Obregon, Toluca, and El Batan), and inter-

1818 national test sites for spring bread wheat.

1819 Two basic types of nurseries are distributed, yield

1820 trials containing 30–50 of the best selected advanced

1821 lines and materials nominated by national program

1822 partners; and, screening nurseries containing up to

1823 200 advanced lines selected for specific targeted traits

1824 and elite genetic diversity. Nurseries are distributed

1825 for spring bread wheat, spring durum wheat, spring

1826 and facultative triticale by CIMMYT from Mexico

1827 (Table 8), and winter and facultative bread wheat

1828 from the Turkey/CIMMYT/ICARDA cooperative

1829 program.

1830 Full pedigree and respective selection history are

1831 known for each line and their phenotypic data cover

1832 yield, agronomic, pathological, and quality traits.

1833 Appropriate data analysis for CIMMYT nurseries

1834 tested worldwide or regionally help to understand

1835 genotype-by-environment interactions (GEI), broad

1836 and specific adaptation and their influence on grain

1837 yield and other traits (Ortiz et al. 2007c and references

1838 therein). The recoding of environmental factors, host

1839 plant resistance to biotic stresses and adaptation to

1840 abiotic stresses provides additional means to account

1841 for the GEI. Such information coupled with an

1842 enhanced knowledge regarding the adaptation and

1843 stability of wheat breeding lines allows a better

1844 targeting of bred-germplasm to specific environments,

1845 particularly in stress-prone areas where reducing the

1846 risk of crop failure and better use of inputs are needed

1847 to ensure maximum performance.

1848 Wheat genetic resources enhancement addressing

1849 global challenges

1850 As the world food situation is being transformed by

1851 new driving forces (von Braun 2007), wheat farmers

1852 and researchers are confronted with major challenges

1853 but also emerging opportunities. It may be that the

1854 ‘‘easy gains’’ from wheat research have been

1855exhausted. Clearly, past impacts from wheat research

1856have been greater in high input farming systems,

1857where semi-dwarf cultivars responded well to the

1858increased use of fertilizers and irrigation. Later,

1859spillovers accumulated as improved cultivars spread

1860from irrigated to higher potential rainfed areas, and

1861then progressively into lower potential rainfed areas

1862(Dixon et al. 2006). Looking to the future, will

1863changing consumer preferences and strengthening

1864market value chains create adequate new markets for

1865quality wheat that will justify increased attention to

1866breeding for quality? Will molecular breeding

1867improve the efficiency of field breeding and acceler-

1868ate the release of dramatically more productive lines

1869and cultivars? Does genetically-modified (GM) wheat

1870have significant potential benefits for the industry and

1871consumers? Will the impact of global climate change

1872require major shifts in wheat research and breeding

1873objectives? Are there improved soil and crop man-

1874agement technologies which would enable farmers to

1875obtain the full benefit of new wheat cultivars, while

1876conserving the resource base for future generations of

1877wheat farmers? Are there proven models of integrated

1878‘‘germplasm enhancement—improved crop manage-

1879ment—or more favorable policy environment’’

1880approaches that might be replicated in major wheat-

1881producing areas?

1882Climate change adaptation and mitigation

1883Climate change could strongly affect the wheat crop

1884that accounts for 21% of food and 200 million ha of

1885farmland worldwide (Ortiz et al. 2008b). The Inter-

1886Governmental Panel on Climate Change (2001)

1887already concluded that ‘‘the model of cereal crops

1888indicated that in some temperate areas potential

1889yields increase with small increases in temperatures

1890but decrease with larger temperature changes’’. As a

1891result of possible climate shifts in the Indo-Gangetic

1892Plains—currently part of the favorable, high poten-

1893tial, irrigated, low rainfall mega-environment, which

1894accounts for 15% of global wheat production—as

1895much as 51% of its area might be reclassified as a

1896heat-stressed, irrigated, short-season production

1897mega-environment (Hodson and White 2007). This

1898shift would also represent a significant reduction in

1899wheat yields, unless appropriate cultivars and crop

1900management practices were offered to and adopted

1901by South Asian farmers.


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1902 To adapt and mitigate the climate change effects

1903 on wheat, supplies for the poor, heat-tolerant wheat

1904 germplasm should be bred. Likewise, wild relatives

1905 of wheat as potential sources of genes with inhibitory

1906 effects on soil nitrification must be assessed.

1907 Adaptation to heat and water stresses

1908 Wheat yield in most tropical and subtropical loca-

1909 tions will decrease due to global warming, which may

1910 be further affected by water scarcity or drought (Ortiz

1911 et al. 2007c). Drought and heat are therefore key

1912 factors with high potential impacts on crop yield

1913 (Barnabas et al. 2008) One approach to solve these

1914 heat- and water-related constraints is improving

1915 wheat germplasm with higher tolerance to stresses

1916 associated with these environments. Hence, wheat

1917 breeders should start genetically enhancing the crop

1918 to maintain yield under higher temperatures or water

1919 scarcity using all available means in the tool kit.

1920 Recognizing water productivity and water-use

1921 efficiency as priorities for wheat, CIMMYT research-

1922 ers disaggregated grain yield under water stress into

1923 distinct components to apply these findings to the

1924 genetic enhancement of this crop (Reynolds and

1925 Borlaug 2006). Ongoing research is providing a

1926 better understanding of traits with major effects on

1927 water productivity in dry land wheat areas (Reynolds

1928 et al. 2007). These include root architecture and

1929 physiological traits, resistance to soil-borne pests and

1930 diseases, tolerance to heat and salinity, and zinc-

1931 deficient and boron toxic soils. The combination of

1932 improved germplasm, the Center and partners’

1933 expertise in drought physiology, soil-borne diseases,

1934 agronomy, and the availability of DNA markers for

1935 various traits place CIMMYT in a unique position to

1936 develop water-productive wheat with resistance to the

1937 important stresses for use by partners throughout the

1938 developing world.

1939 Some important attributes for drought-prone envi-

1940 ronments are available in the wild relatives of wheat

1941 (Reynolds et al. 2007). Re-synthesizing hexaploid

1942 wheat with wild ancestors has been used at CIMMYT

1943 for tapping this useful variation and incorporating

1944 such genetic resources into wheat-bred germplasm

1945 (Dreccer et al. 2007). Recently, Ogbonnaya et al.

1946 (2007) found that such lines deriving from re-synthe-

1947 sizing wheat yielded 8–30% higher than the best local

1948 check in multi-site trials across diverse regions of

1949Australia. Their results reinforce previous research

1950conducted at CIMMYT that lines derived from

1951synthetic wheat have the potential to significantly

1952improve grain yield across environments.

1953In addition to the above undertakings, transgenic

1954approaches for incorporating stress-inducible regula-

1955tory genes that encode proteins such as transcription

1956factors (e.g. DREB1A) into the wheat cultigen pool

1957are also being pursued (Hoisington and Ortiz 2008).

1958The DREB1A gene was placed under the control of a

1959stress-inducible promoter rd29A from Arabidopsis

1960rd29A gene and inserted via biolistic approach into

1961bread wheat (Pellegrineschi et al. 2004). Plants

1962expressing the DREB1A gene demonstrated substan-

1963tial resistance to water stress in comparison with

1964checks under experimental greenhouse conditions

1965manifested by a 10-day delay in wilting when water

1966was withheld. Severe symptoms (death of all leaf

1967tissue) were evident in the controls after 15 days

1968without water. The transgenic wheat lines started to

1969show water-stress symptoms only after 15 days. The

1970greenhouse pot experiments based on severe desic-

1971cation stress do not however represent typical field

1972conditions and, therefore, the plants may not be

1973exhibiting a response that would be valuable in

1974farmers’ fields. Hence, CIMMYT researchers shifted

1975their attention to evaluating transgenic wheat lines in

1976contained field trials. Preliminary results showed that

1977the DREB1A gene in wheat significantly lowers

1978canopy temperature compared with the control in

1979these trials mimicking unpredictable mid-season

1980(vegetative phase) drought (Ortiz et al. 2007a). The

1981gene DREB1A driven by abiotic stress inducible

1982promoter rd29A in wheat seemed to delay develop-

1983ment in the transgenic plants and did not result in

1984better grain yields than the control under both

1985irrigated and water-stress conditions. The growth

1986retardation observed on the over-expression of

1987AtDREB1A using 35S CaMV constitutive promoter

1988was overcome using inducible promoter rd29A in

1989transgenic Arabidopsis (Kasuga et al. 1999) and

1990tobacco (Kasuga et al. 2004). However, in some of

1991the transgenic wheat lines with rd29A:DREB1A,

1992growth retardation was observed, which could be

1993due to background expression of this promoter in

1994wheat. We are now pursuing transgenic wheat plants

1995with DREB1A under different inducible promoters,

1996especially promoters with low background, which

1997only switch on when plants are under certain specific


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1998 stress conditions. For the evaluation of transgenic

1999 wheat plants, pot evaluation is important at early

2000 stage, but it is of great importance to assess

2001 transgenic material in the field as early as possible

2002 to investigate the impact on both plant growth and

2003 grain yield under various appropriate drought-stress

2004 profiles. It is also of interest to investigate at what

2005 stages of growth and in which genetic backgrounds

2006 the transcription factors like DREB1A may have their

2007 most significant effects.

2008 Heat stress already affects wheat plant senescence

2009 and photosynthesis, thereby influencing grain filling.

2010 Wheat cultivars capable of maintaining high 1000-

2011 kernel weight under heat stress appear to possess

2012 higher tolerance to hot environments (Reynolds et al.

2013 1994b). Physiological traits that are associated with

2014 wheat yield in heat-prone environments are canopy

2015 temperature depression, membrane thermo-stability,

2016 leaf chlorophyll content during grain filling, leaf

2017 conductance, and photosynthesis (Reynolds et al.

2018 1998). Amani et al. (1996) used canopy temperature

2019 depression to select for yield under a hot, dry,

2020 irrigated wheat environment in Mexico, whereas

2021 Hede et al. (1999) found that leaf chlorophyll content

2022 was correlated with 1,000-kernel weight while

2023 screening Mexican wheat landraces. Such sources

2024 of alleles coupled with some of the above traits that

2025 defined a new wheat ideotype can provide means for

2026 genetically-enhanced wheat by design in heat-prone

2027 environments.

2028 As indicated above, there are two main wheat

2029 environments in the Indo-Ganges: mega-environment

2030 1 is a favorable, irrigated, low rainfall environment

2031 with high yield potential. In contrast, mega-environ-

2032 ment 5 is a heat-stressed environment (early and late

2033 season heat stress) with available irrigation, but in its

2034 humid and hot areas, the fungi Cochliobolus sativus

2035 cause spot blotch and the Pyrenophora tritici-repentis

2036 (Died.) Drechsler inducing tan spot are pathogens

2037 responsible for leaf blight (Joshi et al. 2007c). These

2038 two major wheat mega-environments in the sub-

2039 continent have been differentiated on the basis of

2040 coolest quarter minimum temperature ranges (3–11�C

2041 for ME-1 and 11–16�C for ME5). In some of the

2042 mega-environment five areas poorer infrastructure,

2043 socio-economic factors, and crop management cou-

2044 pled with the stresses, brought the shortened

2045 vegetative phase and leaf blight ensuing from heat

2046 stress, particularly after flowering stage, which leads

2047to low yield in wheat, the quality of which may be

2048also affected by grain shriveling. Recent data com-

2049piled in the eastern Gangetic plains over 6 years have

2050shown that the higher average temperature observed,

2051especially during the night, was related to higher spot

2052blotch severity and partly explained lower yield

2053performances (Sharma et al. 2007). Disease severity

2054which increases with growth stage depends on crop

2055resilience to heat stress (Duveiller et al. 2005). Thus,

2056improvement of spot blotch resistance in these areas

2057implies a crop physiology adapted to stressed envi-

2058ronments (Sharma et al. 2004). Such observations

2059support, that under global warming, there will be a

2060significant decrease of the most favorable and high

2061yielding mega-environment 1 area due to heat stress,

2062thereby leading to likely yield losses of the wheat

2063grain harvest. Unless appropriate improved germ-

2064plasm, crop husbandry, and resource management are

2065deployed, about 200 million people (based on current

2066population), whose food intake rely on crop harvests

2067in mega-environment 1, will become more vulnerable

2068due to this heat stress affecting the wheat-cropping

2069systems. In this regard, better host plant resistance to

2070leaf blight has been achieved by crossing genetic

2071resistance sources or wild relatives to high-yielding

2072cultivars (Duveiller 2004). Germplasm improvement

2073methods centered on regional partnerships are now

2074more specifically addressing the needs of warmer

2075areas since it is possible to improve host plant

2076resistance of local wheat cultivars based on selective

2077breeding using resistant and agronomically-superior

2078genotypes (Sharma et al. 2004).

2079Mitigation to global warming

2080Nitrous oxide (N2O) is a potent greenhouse gas

2081generated through the use of manure or nitrogen (N)

2082fertilizer and susceptible to de-nitrification, thus often

2083unavailable for crop uptake and utilization. In many

2084intensive wheat-cropping systems common N fertil-

2085izer practices lead to high fluxes of N2O and nitrous

2086oxide (NO). Some plant species show biological

2087nitrification inhibition (BNI) ability that would result

2088in less flux of N2O and NO and retention of N

2089fertilizer for longer time in the soil, which would lead

2090to reducing greenhouse gas. However, wheat, rice,

2091and maize—the most important cereal crops, do not

2092possess BNI (Subbarao et al. 2007b). Leymus

2093racemosus (Lam.) Tzvelev—a wild relative of wheat,


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2094 was found to be a source for inhibiting or reducing

2095 soil nitrification by releasing inhibitory compounds

2096 from roots and suppressing Nitrosomonas bacteria

2097 (Subbarao et al. 2007a). A Leymus chromosome

2098 containing the relevant gene(s) was introduced into a

2099 wheat line that thereafter showed BNI. New research

2100 undertakings are underway to characterize and quan-

2101 tify the biological nitrification inhibition (BNI)

2102 ability from this Leymus-wheat introgression lines

2103 in field trials that may open the path for genetically

2104 enhancing BNI ability in the cultigen pool using this

2105 wild relative as a source for this trait.

2106 Food safety and fighting wheat mycotoxins

2107 Fusarium head blight (FHB) or scab is an important

2108 fungal disease that affects wheat by reducing kernel

2109 weight, yield, and flour-extraction rates in many

2110 important wheat-growing areas in North and South

2111 America, China, and Europe. Several Fusarium

2112 species are associated with scab: Fusarium grami-

2113 nearum Schwabe is the major pathogen worldwide

2114 while F. culmorum (Wm.G. Sm.) Sacc. tends to

2115 predominate in maritime regions (Gilchrist and Dubin

2116 2002). The Fusarium species associated with scab

2117 produce mycotoxins that contaminate the grain. A

2118 number of these compounds have been shown to be

2119 harmful to human and animal health. The mycotoxins

2120 of primary concern with respect to FHB are the

2121 trichothecenes. The most common trichothecene in

2122 grain affected by scab is the mycotoxin known as

2123 deoxynivalenol (DON) produced by F. graminearum

2124 and F. culmorum (Nicholson et al. 2007). A second

2125 trichothecene produced by certain isolates of these

2126 two Fusarium species is nivalenol (NIV). Another

2127 mycotoxin, produced mainly by F. culmorum,

2128 F. graminearum, and F. cerealis (Cooke) Saccardo

2129 is zearalenone (ZEN), a metabolite that is less acutely

2130 toxic and often occurs with trichothecenes (Desjar-

2131 dins 2006; Nicholson et al. 2007). On wheat seedling

2132 tests, the addition of trichothecenes (DON, NIV, and

2133 T-2) to spore suspensions increases lesion size

2134 dramatically, unlike ZEN or mycotoxins produced

2135 by Fusarium species inducing disease on other

2136 cereals. This suggests that trichothecenes play an

2137 important role in lesion development by Fusarium

2138 species associated with FHB (Jiro Murakami,

2139 CIMMYT, unpublished). In recent years, the imple-

2140 mentation of new and more stringent regulations

2141limiting the authorized level of DON in grain and

2142food products has prompted wheat researchers and

2143growers to give more attention to the need to produce

2144wheat with lower amounts of mycotoxins (Ortiz et al.

21452008a).

2146Research toward improved resistance against FHB

2147has been conducted at CIMMYT for more than

214820 years and collaboration with institutes in China,

2149Japan, and Brazil led to the incorporation of superior

2150levels of scab resistance into high-yielding genotypes

2151(Dubin et al. 1996; Ban et al. 2006). However, since

2152the resistance is limited, research is ongoing to

2153expand this resistance base through the identification

2154and validation of QTL associated with field resistance

2155and low levels of DON. In practice, germplasm

2156screening, phenotyping of mapping populations, and

2157detection of novel sources of resistance is conducted

2158under strictly standardized field conditions at El

2159Batan, where CIMMYT is located near Mexico City,

2160under artificial inoculation of F. graminearum iso-

2161lates for which the DON chemotype has been

2162confirmed by the polymerase chain reaction (PCR).

2163At harvest, due to the high cost of mycotoxin

2164detection, only specific research materials and sam-

2165ples of elite wheat germplasm consistently showing a

2166low visual Fusarium head blight index are ground to

2167determine the DON level in the whole grain flour.

2168Analysis for DON content is carried out by means of

2169a commercially available immunoassay test (Rida-

2170screen Fast DON, Biopharm, Germany). CIMMYT is

2171also involved in research aiming at reducing myco-

2172toxin testing costs in particular if a method is used by

2173national research programs. Thus, for selected studies

2174in collaboration with partners in South America,

2175CIMMYT assesses and validates low-cost protocols

2176to determine DON content based on fluorometry

2177(Fuoroquant, Rohmer, Austria). Further applied

2178research includes the validation of quantitative PCR

2179methods aimed at quantifying DON based on the

2180fungal biomass in the grain and the presence of the

2181Tri-5 gene responsible for DON production, analyz-

2182ing the correlation with FHB field symptoms. Other

2183attempts to speed the detection of low DON content

2184in advanced wheat lines included the evaluation of a

2185lateral-flow colloidal gold-based immunoassay for

2186the rapid detection of deoxynivalenol with two

2187indicator ranges (De Saeger et al. 2008).

2188One of the objectives of CIMMYT’s wheat

2189breeding program in coming years is to distribute


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2190 high-yielding wheat germplasm with acceptable end-

2191 use quality and with resistance to FHB which also

2192 harbor a low DON content. Thus, efforts are being

2193 made to add the information on the DON content in

2194 each line when nurseries are distributed (Lewis et al.

2195 2007). Since the main obstacles to provide reliable

2196 quantitative information on resistance to mycotoxins

2197 (i.e., DON) in wheat germplasm are the high field

2198 evaluation and assay costs, understanding the factors

2199 affecting the correlation between phenotypical data

2200 and mycotoxin content is paramount to improve data

2201 accuracy and information reliability.

2202 Grain quality for adding value in the commodity

2203 chain

2204 Globalization, the continuous increase in urbaniza-

2205 tion, and improvements in the income of people in

2206 developing countries have been generating a large

2207 demand for wheat crops possessing specific quality

2208 traits. For example, consumption of western style

2209 food such as pan bread and cookies are increasing

2210 rapidly in large wheat-producing countries such as

2211 China and India, and consumption of flat breads and

2212 flour noodles are becoming popular as convenience

2213 foods in the western hemisphere. In addition, the

2214 demand for high quality traditional products such as

2215 noodles, steamed bread, flat breads, pasta or couscous

2216 among others, is also increasing quickly. Hence,

2217 grain-processing quality and quality uniformity are

2218 becoming more important breeding issues in devel-

2219 oping countries. In wheat breeding, improving wheat

2220 productivity, disease resistance, and tolerance to

2221 biotic stresses and wheat quality attributes need to

2222 be addressed holistically to develop wheat cultivars

2223 satisfying both the producer and the consumer and in

2224 order to maintain competitive and sustainable pro-

2225 duction systems.

2226 End-use quality traits

2227 Flour yellowness is undesirable for producing breads

2228 and most Asian flour noodles (Liu et al. 2003), except

2229 for yellow alkaline flour noodles. In contrast, in

2230 durum wheat semolina, a high concentration of

2231 yellow carotenoids (mainly lutein) is highly desir-

2232 able, for it results in bright, yellow pasta products.

2233 Sprouted grain shows high alpha-amylase activity,

2234 which negatively affects the processing quality of

2235bread-, cake- and cookie-making. Sound wheat may

2236present different levels of poly-phenol oxidase activ-

2237ity, which promote the time-dependent darkening of

2238cooked Asian noodles (Anderson and Morris 2003),

2239and of lipoxygenase, which promotes the oxidation of

2240carotenoids reducing pasta yellowness (Leenhardt

2241et al. 2006).

2242Hard wheat produces flours with much higher levels

2243of starch damage and water absorption as compared to

2244soft wheat. This difference in water-absorption capac-

2245ity makes soft wheat (and not hard wheat) suitable for

2246cookie making and hard wheat (and not soft wheat)

2247suitable for bread making (Souza et al. 2002). Grain

2248hardness is influenced mainly by allelic variations and

2249is closely linked to puroindoline genes. Cane et al.

2250(2004) observed that some allelic variations of Pina

2251show differential effects on milling yield.

2252The main factor determining wheat end-use is the

2253gluten protein. Gluten is composed of monomeric

2254gliadins and polymeric glutenins. Allelic variations

2255controlling gliadin and glutenin composition (mainly

2256at the Glu-1, Glu-3, and Gli-1 loci), are responsible

2257for most variation in dough properties (strength and

2258extensibility), dough-mixing properties, and bread-

2259and Chinese noodle-making quality (Branlard et al.

22602001; He et al. 2005; Liu et al. 2005). In durum

2261wheat, the best pasta-cooking quality is achieved

2262from wheat possessing Glu-B3 LMW-2 type alleles

2263(Pena and Pfeiffer 2005 and references therein).

2264Granule-bound starch synthase (GBSSI) is respon-

2265sible for amylose synthesis in the grain. Grain

2266amylose levels are affected by allelic variations of

2267the Wx gene complex (Geera et al. 2006). Starch

2268pasting viscosity affects the eating quality of wheat

2269flour noodles, particularly Japanese white noodles,

2270which are smooth, soft, and slightly elastic (Crosbie

22711991). Increased starch-swelling power and desirable

2272noodle softness have been associated with the

2273absence of GBSSI controlled by the Wx-B1a gene

2274on chromosome 4A (Ross et al. 1996).

2275Quality testing methodology

2276CIMMYT addresses wheat quality improvement by

2277examining and defining several factors associated

2278with wheat processing and end-use quality, and by

2279applying diverse molecular and conventional analyt-

2280ical and screening tools required to achieve the

2281improvement of relevant grain quality-related traits.


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2282 Ongoing research in China and Mexico are examples

2283 of this approach.

2284 Knowledge about the genetic control and the

2285 influence of allelic variants of main traits (Table 10)

2286 is fundamental for efficient quality improvement.

2287 However, we cannot ignore that some of these quality

2288 traits may be strongly influenced by genotype-by-

2289 environment (heat, drought, high humidity) interac-

2290 tions (Eagles et al. 2002; Spiertz et al. 2006) and

2291 nutrient availability, particularly at the grain-filling

2292 stage (Dupont et al. 2006).

2293 At CIMMYT electrophoresis (SDS-PAGE) is

2294 commonly used to identify allelic variations at Glu-

2295 1, Glu-3, and Gli-1 in parental lines. In addition,

2296 rapid, small-scale tests including marker-assisted

2297 selection (MAS), near-infrared spectroscopy (NIRS),

2298 SDS-sedimentation, and dough rheology, are applied

2299 at different stages of the breeding process. MAS

2300 offers the best option for specific traits controlled by

2301 single genes because it is performed on leaf tissue

2302 before seed-setting. The flour sedimentation test,

2303 NIRS, and the mixograph, on the other hand, allow

2304 rapid estimation of important physical, composi-

2305 tional, and functional grain and flour factors closely

2306 associated with milling and wheat processing quality.

2307 Finally, the use of flour and dough-testing method-

2308 ologies (milling yield, dough viscoelasticity, starch

2309 pasting properties, and actual end-product quality)

2310 allow characterizing more specifically for processing

2311 and end-use quality attributes of advanced lines of

2312 spring and winter/facultative germplasm.

2313 Breeding strategy, quality testing, and screening

2314 In setting breeding priorities and strategies, one must

2315 determine: the cultivar’s intended end-uses and the

2316demands of the targeted market, specific quality traits

2317to breed for, and genotype-by-environment-by-man-

2318agement interactions that may influence the quality of

2319the resulting cultivar.

2320Information on glutenin and gliadin subunit com-

2321position helps in the designing of crosses aimed at

2322achieving allelic combinations known to contribute

2323positively to dough properties required for producing

2324leavened and flat breads, flour noodles, cookies, and

2325pasta. Screening may initiate in F4–F5 applying MAS

2326for desirable quality-related genes or allelic varia-

2327tions. When possible, the use of rapid, high-

2328throughput conventional small-scale tests (e.g. SDS-

2329sedimentation and NIRS) should be used in addition

2330to MAS to screen for complex traits under multigenic

2331control. Because MAS and conventional small-scale

2332quality tests explain end-use quality only partially

2333(Graybosch et al. 1999; Kuchel et al. 2006), it is

2334advisable to apply quality screening based on more

2335specific processing traits (dough viscoelasticity and

2336mixing properties, starch pasting properties, baking

2337performance) and end-product quality attributes in

2338advanced breeding stages; i.e., F6–F9 (Pena et al.

23392002; Souza et al. 2002). Finally, multi-location yield

2340trials exposing advanced elite lines to environmental

2341variation (and farmers’ crop management practices)

2342are necessary to identify the few genotypes combining

2343stable yield and quality attributes across locations.

2344China and CIMMYT have had a very strong and

2345close collaboration regarding germplasm exchange,

2346human resource development, and in the establish-

2347ment of diverse analytical tests efficient to improve

2348bread and noodle quality attributes. ‘Jinan 17’ and

2349‘Jimai 19’ are former leading cultivars in northern

2350China, and ‘Jinmai 20’ and ‘Yumai 34’ are good pan-

2351bread making quality and leading cultivars in the

Table 10 Main wheatquality traits and theirgenetic control

Quality trait Loci Chromosome

Grain hardness (puroindolins) PinA-D1, PinB-D1 5DS

Alpha amylase Amy-1, Amy-2 Groups 6 and 7

Poly phenol oxidase Ppo-A1, Ppo-D1 2AL, 2D

Protein content Pro-1, Pro-2 5D

Glutenins Glu-1, Glu-3 1A, 1B, 1D

Gliadins Gli-1, Gli-2 Groups 1 and 6

Secalins Sec-1 1R

Starch granule-bound synthase Wx-A1, Wx-B1, Wx-D1 7AS, 4AL, 7DS

Yellow Pigment PsyA1, Psy-B1 7A, 7B


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2352 Yellow and Huai Valleys. They derived from

2353 CIMMYT-bred germplasm. Improvement of gluten

2354 quality is the top priority for quality breeding in

2355 China. SDS sedimentation value, mixograph param-

2356 eters, and high- and low- molecular weight glutenin

2357 subunits are primarily used for characterization of

2358 crossing parents and selection in early generations.

2359 Selection of desirable grain hardness Pin-B1 alleles

2360 (Pinb-D1b) is highly desirable. Grain hardness, SDS

2361 sedimentation, peak viscosity, polyphenol oxidase

2362 (PPO) activity and yellow pigment content, can be

2363 used to screen for Chinese white noodle quality in the

2364 early generation of a wheat breeding program;

2365 molecular markers for selection of PPO activity (He

2366 et al. 2007), yellow pigment content (He et al. 2008),

2367 and high starch viscosity (Briney et al. 1998) are also

2368 available for screening. Molecular markers have been

2369 routinely used to characterize crossing parents and for

2370 confirmation of the presence of targeted genes in

2371 breeding programs, both in Mexico and China. Two

2372 multiplex PCR assays targeting improvement of

2373 bread-making quality (including five genes) and of

2374 noodle quality (including three genes) were also

2375 developed to improve the efficiency and reduce the

2376 costs of applying MAS in wheat breeding programs

2377 (Zhang et al. 2008).

2378 Future challenges in quality improvement

2379 The future challenge is to improve dough extensibility

2380 and quality stability. The combination of high yield

2381 potential and good quality and integration of diverse

2382 quality donors from wheat relatives is advisable.

2383 Wheat breeders still face the challenge of unveiling

2384 the complex mechanisms involved in genotype-by-

2385 environment-by-management interactions affected by

2386 heat, drought, erratic climate, nutrient availability

2387 during grain development, among other factors that

2388 significantly influence yield and quality stability

2389 (Dupont et al. 2006; Eagles et al. 2002; Geera et al.

2390 2006; Spiertz et al. 2006). Furthermore, an excess of

2391 three billion people in the world are affected by

2392 micronutrient deficiencies that cause serious health

2393 problems. In addition, obesity and associated illnesses

2394 are becoming serious public health problems in many

2395 parts of world. Breeders need to immediately start

2396 serious undertakings to improve wheat nutritional

2397 value and health-related issues associated with the

2398 consumption of wheat-based foods.

2399Human nutrition/health and wheat biofortification

2400Zinc deficiency is implicated in health problems

2401throughout the world, especially across a wide band

2402of countries in West Asia, North Africa, and the

2403South Asian subcontinent where more than half of

2404inhabitants’ daily calories come from wheat (CI-

2405MMYT 2004). In South and West Asia, millions of

2406heavy wheat consumers are also iron deficient.

2407Women and children are particularly prone to zinc

2408and iron malnutrition.

2409The health of poor people may be enhanced by

2410breeding staple food crops that are rich in micronu-

2411trients, a process referred to as biofortification. In

24122003, the CGIAR launched the Challenge Program

2413HarvestPlus with the aim of breeding and dissemi-

2414nating crops for better nutrition. Within this global

2415alliance undertaking, CIMMYT is developing high-

2416yielding wheat cultivars with grain containing

241730–50% more iron and zinc (Ortiz-Monasterio et al.

24182007). The potential impact is dramatic given that

2419wheat cultivars bred by CIMMYT and its partners

2420cover 80% of the global spring wheat area.

2421The best sources of these micronutrients are wild

2422species that do not cross easily with modern wheats

2423(Cakmak et al. 2000). Researchers have therefore

2424developed a ‘‘bridge’’ line by crossing one such grass

2425(Ae. tauschii) with a high-micronutrient primitive

2426wheat (Triticum dicoccon Schrank). The resulting

2427‘‘bridge’’ lines combine readily with modern wheat

2428cultivars, producing lines whose grain contains more

2429iron and zinc than modern wheat. Partners in India

2430and Pakistan are using this approach to develop high-

2431yielding, disease-resistant, biofortified wheat for

2432South Asia.

2433In Turkey, home to pioneering research on zinc

2434deficiency and wheat, wheat landraces and cultivars

2435that take up and use zinc more efficiently are being

2436combined with wheat cultivars that have resistance to

2437yellow rust and root diseases (CIMMYT 2004).

2438CIMMYT researchers, with partners from labs else-

2439where, are identifying molecular markers for genes

2440that control grain iron and zinc levels, to facilitate

2441their transfer to new cultivars.

2442Recent research undertaken by CIMMYT on iron

2443and zinc losses in milling and cooking, suggests that

2444milling reduces Fe and Zn levels in the flour but

2445hydrate is reduced even more which results in a more

2446favorable Zn/hydrate ratio, which is highly correlated


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2447 with bioavailability (Ortiz-Monasterio unpublished

2448 results). A flour extraction rate of 80% is best to

2449 optimize function of increasing bioavailability versus

2450 decreasing content with decreasing flour extraction.

2451 This and the center’s research on bio-availability will

2452 help determine exactly how much it helps to eat

2453 biofortified daily bread.

2454 Empowering rural people through participatory

2455 wheat improvement and seed systems

2456 Three-quarters of the world’s poorest people live

2457 below US$ 1 a day of which 37% are in South Asia.

2458 In this region, particularly in the eastern Indo-

2459 Gangetic Plains, there is a high level of poverty,

2460 malnutrition, and food insecurity. The number of

2461 poor people is expected to increase still further as

2462 population growth exceeds that of agriculture pro-

2463 ductivity. Wheat, covering an area of some

2464 37 million ha, is one of the economic mainstays in

2465 the region. However, the productivity of wheat

2466 cropping systems lags far behind its potential. Hunger

2467 is inextricably linked to poverty and vulnerability.

2468 The millennium development goal of the elimination

2469 of extreme poverty and hunger can only be met by

2470 increases in agricultural productivity, particularly by

2471 resource-poor farmers, which is fundamental to

2472 growth and poverty reduction in the region.

2473 South Asia produced 101.3 million t of wheat in

2474 2007. India and Pakistan harvested 74.9 and 23.3 mil-

2475 lion t, respectively. In spite of this output, the region

2476 is projected to have a wheat deficit of 21 million t by

2477 2020 (Agcaoili-Sombilla and Rosegrant 1994). If

2478 these projections are correct, Pakistan will have the

2479 highest deficit with 15 million t, followed by Bangla-

2480 desh with 4 million t. India would have to increase its

2481 production from the current 74.9 million t to about 90

2482 (Joshi et al. 2007b) or 109 million t by year 2020

2483 (Nagarajan 2005). To achieve this output, the average

2484 national wheat yield would have to increase from its

2485 current 2.63 t ha-1 to almost 4 t ha-1 in the next

2486 12 years. This is a significant challenge given that

2487 resources for research in these countries are shrinking

2488 and that the present estimated yield gap between

2489 farmers and experimental yields is about 1.8 t ha-1

2490 (Ortiz-Ferrara et al. 2007a).

2491 Surveys conducted in the region suggest that one

2492 of the main causes of low yields is the predominance

2493 of older (at least 1.5 decades) wheat cultivars. These

2494cultivars are genetically inferior to more recently

2495bred-germplasm, and are increasingly susceptible to

2496diseases. Seed replacement is around 10% and there

2497is significant lack of access to seed of appropriate

2498cultivars, especially for those that are adapted to

2499marginal environments. The varietal adoption trends

2500described above are in large part due to the poor

2501extension and weak seed production systems pre-

2502valent in most of these countries. Hence, a system for

2503dissemination of new technologies and for develop-

2504ing community seed industry by local farmers and

2505their groups is important to empower rural people. It

2506is essential to promote new materials and to also

2507make crop production more profitable for farmers.

2508CIMMYT, in partnership with the Center for Arid

2509Zone Studies-Natural Resources (CAZS-NR, Bagor,

2510Wales), has been collaborating with farmers, national

2511programs, and other South Asian partners to promote

2512improved wheat cultivars and new resource-conserv-

2513ing technology (RCT) options in farmers’ fields.

2514Participation fostered among farmers, scientists,

2515extension specialists, non-governmental organiza-

2516tions (NGOs), and the private sector includes

2517participatory variety selection (PVS), and participa-

2518tory evaluation of agronomic practices. Through

2519PVS, several farmer-preferred technologies have

2520been identified including wheat cultivars for adverse

2521conditions in eastern Uttar Pradesh, India (Singh et al.

25222007), and for boron deficiency in some locations of

2523Nepal. There has been considerable improvement in

2524farmers’s access to new cultivars and technologies in

2525the rural areas. Yield increases (15–70%) have been

2526achieved by resource-poor farmers through the

2527adoption of new cultivars and RCT. The farmers

2528have also made substantial cost savings and achieved

2529higher yields through resource-conserving agronomic

2530techniques such as zero- or reduced-tillage. Seed of

2531the new farmer-selected cultivars has been multiplied

2532by groups of collaborating farmers and widely

2533distributed.

2534Following this participatory research, several

2535thousands of farming households have rapidly

2536adopted cultivars and benefited from them. Seed

2537saving by farmers and farmer-to-farmer seed spread

2538of new cultivars has been evident which has brought

2539sustainable impact. Strengthening and capacity-build-

2540ing of local institutions including community-based

2541seed production and distribution has also been taking

2542place. Both men and women farmers have been


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https://www.researchgate.net/publication/226164722_Wheat_improvement_in_India_Present_status_emerging_challenges_and_future_prospects?el=1_x_8&enrichId=rgreq-b97bd0b2e59dcb0078850802c561253d-XXX&enrichSource=Y292ZXJQYWdlOzIyNTgyMDgyMztBUzoxMDQxNTU1MzY0MjkwNzFAMTQwMTg0NDAyMzQ3Nw==

https://www.researchgate.net/publication/225729145_High_yielding_spring_wheat_germplasm_for_global_irrigated_and_rainfed_production_systems?el=1_x_8&enrichId=rgreq-b97bd0b2e59dcb0078850802c561253d-XXX&enrichSource=Y292ZXJQYWdlOzIyNTgyMDgyMztBUzoxMDQxNTU1MzY0MjkwNzFAMTQwMTg0NDAyMzQ3Nw==

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2543 participating in this partnership in various activities

2544 addressing gender perspective and empowerment

2545 issues. They are willing to collaborate with all of

2546 the partners to improve the returns to wheat cropping

2547 systems through participatory approaches.

2548 Partnerships for development, dissemination, and

2549 adoption of improved technologies for improving

2550 wheat productivity

2551 Participatory research and development has been

2552 reported as an efficient approach for up-scaling new

2553 agricultural technologies (Ortiz Ferrara et al. 2001;

2554 Witcombe et al. 2001). It is capable of better

2555 addressing farmers’ problems that very often are

2556 not recognized due to the complexity of farmers’

2557 different situations and the vast diversity in farmers’

2558 fields. Participatory research has been used to com-

2559 plement ongoing research to help farmers by

2560 providing them with a wider choice of options to

2561 evaluate under their own conditions (Witcombe et al.

2562 1996, 2005).

2563 The ‘‘mother-baby’’ trial system, which was suc-

2564 cessfully used for maize in sub-Saharan Africa

2565 (Snapp 1999; de Groote et al. 2002), proved to be

2566 an efficient approach for developing and disseminat-

2567 ing new cultivars and RCT options through close

2568 collaboration with farmers. Under this approach, a

2569 large number of ‘‘mother-baby’’ trials are grown in

2570 different villages to provide better options for farm-

2571 ers. The ‘‘mother’’ trial consists of 12–15 elite wheat

2572 lines or recently released cultivars, which include as

2573 check the most popular cultivars grown by farmers at

2574 each site. A number of ‘‘baby’’ trials, consisting of

2575 just one of the elite cultivars in the ‘‘mother’’ trial

2576 plus a local check, are grown around the ‘‘mother’’

2577 trial in the same year. Also, seed multiplication plots

2578 of all the genotypes in the ‘‘mother’’ and ‘‘baby’’

2579 trials are planted simultaneously to harvest clean

2580 seeds. Bred-lines and cultivars in the ‘‘mother’’ and

2581 ‘‘baby’’ trials are assessed in a collaborative and

2582 consultative mode by farmers. Quantitative feedback

2583 is analyzed and used to ascertain farmers’ prefer-

2584 ences. Clean seed of the farmer-selected cultivars is

2585 distributed to collaborating farmers. In the following

2586 year, farmers’ selected genotypes are tested in large

2587 fields along with the farmers’ local cultivar. Farmers

2588 are trained on seed production to harvest quality seed

2589 from the large plots in the second year. In this way,

2590farmers have clean seed of their preferred cultivars

2591for further planting. Often the participating farmers

2592harvest more seed than they need. The additional seed

2593is sold to other farmers in the community. Thus the

2594new cultivars are spread from farmer to farmer.

2595Experiences in improving food security and income

2596generation

2597In Nepal, a total of 26 wheat cultivars were tested in

259863 villages in seven districts from 2002 to 2005.

2599These cultivars were tested in a wide range of

2600environments using two different sets of PVS

2601‘‘mother’’ trials. As a result, about seven bred-lines

2602or cultivars were identified by participating farmers.

2603Three released cultivars are under extensive seed

2604multiplication by the public seed industry. Farmers in

2605the southern lowlands and in the mid-central hills of

2606the Kathmandu Valley are also involved in commu-

2607nity seed production. These adoption trends have

2608helped farmers in those areas to increase food

2609sufficiency (i.e., households with sufficient food for

2610the year) from 65% in 2002 to 71% in 2005. Also,

2611there were households with food sufficiency for

2612longer period in 2005 compared to 2002. These gains

2613in food sufficiency are primarily attributed to three

2614factors. The farmers reported that of the gains in food

2615sufficiency, 41.3% was due to the cultivar, 44.4%

2616from crop management including fertilizers, and

261714.3% from irrigation. Farmers in Bangladesh have

2618identified at least three new wheat cultivars since

26192005. Farmers who have adopted them have

2620increased their income (Table 11). The yield increase

2621over the widely popular cultivar ‘Kanchan’ was

2622705 kg, which translates into additional income of

2623about US$ 164 ha-1. Varietal diversification and

2624income generation has also increased in eastern India

2625as a result of collaboration with the Indian Council of

2626Agricultural Research (ICAR) and the Rice-Wheat

2627Consortium for the Indo-Gangetic Plains (RWC).

2628Many farmers in Uttar Pradesh are successfully

2629engaged in community seed production. At one of

2630the sites, around one-third of the area came under

2631seed production after 3 years of PVS. In general,

2632farmers at the PVS sites recorded greater profits than

2633at non-PVS sites. Around 83% of the farmers at the

2634PVS sites responded that they were making a profit of

2635at least US$ 67 ha-1. The profit increase was mainly

2636due to increases in productivity, decreases in the cost


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2637 of cultivation, and improved earnings due to quality

2638 seed production of farmer-preferred cultivars. Based

2639 on this new outcome, participatory seed production

2640 was carried out at all the locations where PVS

2641 activities were conducted with the objective of

2642 equipping and training farmers for seed production

2643 of high-yielding cultivars. As a result, they could

2644 multiply seed of their preferred cultivars and not be

2645 dependent on outside sources. This approach was

2646 expected to enhance farmers’ profitability through

2647 lowered seed costs, lower costs of production due to

2648 the adoption of RCT, and surplus grain from higher

2649 production. This concept could be extended to other

2650 crops. The participatory seed production was found

2651 extremely useful for participating farmers, since at

2652 almost all the locations they were able to learn to

2653 produce their own high quality seed. The impact of

2654 participatory seed production is being realized for the

2655 first time on such a wide scale in the area and several

2656 farmers’ societies for seed production have been

2657 established in eastern Uttar Pradesh and the bordering

2658 districts of Bihar. This farmer-participatory approach

2659 has helped resource-poor farmers improve their

2660 livelihoods, while ensuring staple food for the region

2661 through the adoption of new cultivars and other RCT

2662 options.

2663 Ug 99 stem rust as a global emerging threat

2664 to wheat (food) supply

2665 Stem or black rust of wheat is historically known to

2666 cause severe devastation; however, it remained under

2667 control for almost 40 years through the use of host

2668 plant resistance. In 1998, severe stem rust infections

2669 were observed on wheat in Uganda, and a race,

2670 commonly known as Ug99 (TTKSK on North

2671 American nomenclature system) with virulence on

2672resistance gene Sr31, which was initially transferred

2673from rye to wheat, was identified. Race Ug99 was

2674subsequently detected in Kenya and Ethiopia in 2005,

2675in Sudan and Yemen in 2006, and in Iran in 2007. It

2676is predicted that Ug99 will continue to migrate to

2677North Africa, the Middle East, South Asia, and

2678beyond through winds or other means. The most

2679striking feature of Ug99 is that it not only carries

2680virulence to gene Sr31 but also this unique virulence

2681is present together with virulence to most of the genes

2682of wheat origin, and virulence to gene Sr38 intro-

2683duced into wheat from Aegilops ventricosa Tausch.

2684and bred in several European and Australian cultivars

2685and a small portion of new CIMMYT germplasm

2686(Singh et al. 2006). This virulence combination might

2687have accounted for the wide-spread Ug99 suscepti-

2688bility in wheat cultivars worldwide. New variants of

2689this race with virulence to Sr24 and Sr36 were

2690detected in Kenya in 2006 and 2007, respectively. It

2691is anticipated that mutation toward more complex

2692virulence will likely occur as the fungal population

2693size increases and selection pressure is placed on the

2694population by cultivars protected by additional race-

2695specific resistance genes. It is estimated that between

269690 and 95% of the global wheat area is planted with

2697wheat cultivars that are susceptible to Ug99 or its

2698new variants.

2699The Borlaug global rust initiative

2700Reducing the area planted to susceptible cultivars in

2701primary risk areas of East Africa, the Arabian

2702Peninsula, North Africa, the Middle East, and West/

2703South Asia is the best strategy if major losses are to

2704be avoided. The ‘‘Borlaug Global Rust Initiative’’

2705(www.globalrust.org), launched in 2005, is using the

2706following strategies to reduce the possibilities of

Table 11 Income change in villages at Daulatpur, Hatiari and Jogda (Dinajpur, Bangladesh) due to farmer-preferred wheat cultivarsand adoption of recommended practices after participatory varietal selection (2002–2005)

Wheat Cultivar Area(ha)

Yield(kg ha-1)

Yieldincrease(kg ha-1)

Seedsaved(kg ha-1)

Seedsaved in52% area(kg)

Price of Additionalincome

Add prod(91,000 Tk)a

Saved Seed(91,000 Tk)

91,000Tk

Tk/ha

Old popular cultivar ‘Kanchan’ 67.71 2,274

Farmer-preferred cultivars 40.96 2,979 705 80 1,704 361.0 27.26 388.26 9,479

Total 108.67 2,540 266 4,521 361.3 72.34 433.64 3,990

a Tk = Taka local currency, i.e., US$ 1 = Tk 58


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2707 major epidemics: monitoring the spread of race Ug99

2708 beyond eastern Africa for early warning and potential

2709 chemical interventions, screening of released varie-

2710 ties and germplasm for resistance, distributing

2711 sources of resistance worldwide for either direct use

2712 as varieties or for breeding, and breeding to incor-

2713 porate diverse resistance genes and adult plant

2714 resistance into high-yielding adapted cultivars and

2715 new germplasm. An aggressive strategy to identify

2716 and promote high-yielding, resistant cultivars is the

2717 only viable option to reduce potential losses as

2718 resource-poor and commercial farmers in most of

2719 Africa, the Middle East, and Asia cannot afford

2720 chemical control or may not be able to apply chem-

2721 icals in the event of large scale epidemics due to their

2722 unavailability for timely application. Reduction of

2723 susceptible cultivars throughout the primary risk area

2724 should reduce wind dispersal of spores from these

2725 areas to the secondary risk areas.

2726 Strategy to breed race-specific resistance genes

2727 The high frequency of the highly resistant wheat

2728 materials from South America, Australia, the USA,

2729 and CIMMYT was identified through the 2005 and

2730 2006 screenings with Ug99 in Kenya. They possess

2731 Sr24, located on the Th. elongatum translocation on

2732 chromosome 3DL together with the leaf rust resis-

2733 tance gene Lr24. The presence of race TTKST with

2734 Sr24 virulence at low frequencies in Ug99 lineage

2735 during 2006 resulted in a rapid buildup sufficient to

2736 cause an epidemic on the Sr24-carrying cultivar

2737 ‘Kenya Mwamba’ in 2007, which occupied about

2738 30% of the Kenyan wheat area. The situations

2739 described above have once again reminded us of

2740 the consequence of dependence on single race-

2741 specific genes in the control of stem rust in areas

2742 where rust is endemic.

2743 Diverse sources of effective race-specific resis-

2744 tance genes, mostly derived from wheat relatives, are

2745 available for breeding. Genes Sr25 and Sr26, derived

2746 from Th. elongatum, have been previously used

2747 successfully in developing cultivars. Other genes,

2748 practically not used in wheat improvement but that

2749 may have good chances of succeeding are Sr27 of rye

2750 origin, and Sr22 and Sr35 derived from T. monococ-

2751 cum. Although alien resistance genes Sr29, Sr32,

2752 Sr33, Sr37, Sr39, Sr40, and Sr44 have not been used

2753 widely in breeding, preliminary experience has

2754indicated their association with unwanted agronomic

2755traits and therefore sizes of alien chromosome

2756segments must be reduced before they can be used

2757successfully. The undesignated resistance genes

2758SrTmp (wheat origin), SrR and Sr1A.1R (rye origin),

2759and a few other uncharacterized sources originating

2760from re-synthesized hexaploid lines or bread wheat

2761offer further diversity.

2762The fastest way to reduce the susceptibility of

2763important wheat cultivars and the best new germ-

2764plasm is to systematically incorporate diverse sources

2765of resistance through limited or repeated backcross-

2766ing. Because most of these Ug99-effective genes are

2767of alien origin, co-segregating molecular markers for

2768some of them are already available and being used for

2769selection at CIMMYT. To avoid fast breakdown, the

2770best strategy is to use race-specific resistance genes in

2771combinations. Molecular markers provide a powerful

2772tool to identify plants that carry combinations of

2773resistance genes. Markers for other genes need to be

2774developed to facilitate their utilization.

2775One major issue remains in that various currently-

2776effective resistance genes are already present in some

2777advanced spring breeding materials that are being

2778tested in various countries to mitigate the immediate

2779threat from Ug99. Whether of not they should they be

2780deployed until their combinations are developed, is a

2781difficult issue to resolve, and there is a wide range of

2782opinions on the matter. This has provoked the

2783CIMMYT wheat improvement group to focus their

2784breeding efforts towards breeding minor genes based

2785on adult plant resistance, especially for areas consid-

2786ered to be under high risk and where survival of the

2787pathogen for several years is expected due to the

2788presence of susceptible hosts and favorable environ-

2789mental conditions. It is thought that this strategy will

2790allow other areas of the world, especially facultative

2791and winter wheat growing regions to use race-specific

2792resistance genes more successfully in their breeding

2793programs.

2794Identification and breeding for complex adult plant

2795resistance

2796Durable stem rust resistance of some of the older US,

2797Australian, and CIMMYT spring wheat lines and

2798cultivars is believed to be due to the deployment of

2799Sr2 in conjunction with other unknown minor,

2800additive genes that could have originated from


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2801 ‘Thatcher’ and the ‘Thatcher’-derived line ‘Chris’

2802 (Singh et al. 2006). Sr2 can be detected through its

2803 complete linkage with pseudo-black chaff phenotype.

2804 Genotypes with negligible expression of pseudo-

2805 black chaff can be selected in breeding materials. Sr2

2806 does not confer adequate resistance under high

2807 disease pressure when present alone. It was detected

2808 in several highly-resistant old, tall Kenyan cultivars,

2809 including ‘Kenya Plume’ and the CIMMYT-derived

2810 semi-dwarf wheat lines ‘Pavon 76,’ ‘Kritati,’ and

2811 ‘Kingbird.’ ‘Pavon 76’ and ‘Kiritati’ were resistant

2812 since the initiation of rigorous screening in 2005 at

2813 Njoro (Kenya) with maximum disease scores of

2814 20MR-MS. ‘Kingbird,’ a new advanced line, is at

2815 present the best known source of adult plant

2816 resistance in semi-dwarf wheat with maximum score

2817 recorded to be 5 MR-MS during the same period.

2818 Because these wheat lines are susceptible as seedlings

2819 with Ug99, their resistance is speculated to be based

2820 on multiple additive genes where Sr2 is an important

2821 component.

2822 With the exception of Sr2, little is known on the

2823 genes involved in durable adult plant resistance.

2824 However, earlier work done by Knott (1982),

2825 knowledge on durable resistance to leaf and yellow

2826 rusts (Singh et al. 2004), and observations made on

2827 breeding materials and a F6 mapping population

2828 involving ‘Pavon 76,’ indicate that the rate of rust

2829 progress is a function of the cumulative effect of the

2830 number of minor genes present in a genotype and the

2831 individual effects of each gene. Accumulation of four

2832 to five slow-rusting, minor genes is therefore

2833 expected to retard disease progress to rates that result

2834 in negligible disease levels at maturity under high

2835 disease pressure, described as ‘‘near-immunity’’ by

2836 Singh et al. (2000).

2837 Because a large portion of CIMMYT high-yielding

2838 spring wheat germplasm does not carry effective

2839 race-specific stem rust resistance genes to Ug99 and

2840 several lines were identified to carry at least moderate

2841 levels of resistance, we view this as a perfect

2842 opportunity to reconstitute high levels of adult plant

2843 resistance in new wheat materials. Due to the lack of

2844 molecular markers for adult plant resistance genes

2845 and the absence of the Ug99 race in Mexico, a shuttle

2846 breeding scheme between two Mexican sites and

2847 Njoro was initiated in 2006 to transfer or accumulate

2848 high levels of adult-plant resistance identified in

2849 semi-dwarf CIMMYT wheat lines to a range of

2850important wheat germplasm. We expect that the

2851frequency of advanced lines which carry high yield

2852potential and maintain wide adaptation, end-use

2853quality characteristics, and high levels of resistance

2854to all three rusts, will increase over time through the

2855use of the Mexico-Kenya shuttle breeding.

2856Replacing susceptible cultivars in Africa, the Middle

2857East, and Asia

2858Screening in Kenya during 2005, 2006, and 2007 has

2859identified a few resistant released cultivars or

2860advanced breeding materials at various stages of

2861testing in most of the countries that submitted their

2862materials for screening. One strategy is to find ways

2863to ensure that the best, high-yielding resistant mate-

2864rials occupy at least 5% of total wheat area

2865distributed throughout the wheat region and are

2866readily available for use as seed in the case that

2867Ug99 establishment is evident in a particular country.

2868To occupy a large area the resistant cultivars must

2869have superior yields to current popular cultivars. This

2870objective is achievable as most of the current popular

2871cultivars were bred during early- to mid-1990s, and

2872the yield potential of current CIMMYT spring wheat

2873germplasm has progressed significantly since then.

2874Yield performances of 14 new high-yielding, Ug99-

2875resistant wheat lines together with current cultivars

2876were determined during the 2006–2007 crop season

2877at 27 sites in India, Pakistan, Nepal, Afghanistan,

2878Iran, Egypt, Sudan, Syria and Mexico. Results show

2879that at least three lines, possessing race-specific or

2880adult plant resistance, in each country showed yield

2881superiority in the range of 10–15% over the current

2882local cultivars. These superior lines are being tested

2883more extensively during the 2007–2008 season for

2884their performance in the above countries and seed is

2885being multiplied simultaneously. Testing of addi-

2886tional wheat materials, mostly with adult plant

2887resistance, is also underway.

2888Fitting bred-genotypes into sustainable

2889and improved crop management practices

2890Crop system management research adds value to

2891improved germplasm by increasing the degree to

2892which yield potential is achieved—about half of the

2893increase in wheat productivity at the farm level is

2894often attributed to crop system management and more


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2895 in stressed environments—and there is often synergy

2896 between these effects (the G 9 System interaction).

2897 CIMMYT holds a unique comparative advantage for

2898 such research at the interface between crop improve-

2899 ment and crop system management.

2900 Figure 5 shows the important role of crop man-

2901 agement regarding maximizing yield potential. The

2902 lower line shows the yields of a historical set of

2903 wheat cultivars bred from 1962 to 1988 based on

2904 applying the current crop management practices that

2905 were used at that time by station management for the

2906 fully irrigated yield trials to determine the yield

2907 potential for new CIMMYT materials. The upper line

2908 presents the yields for the same set of lines but

2909 following improved crop management practices that

2910 incorporated the use of deep chiseling to break up

2911 existing soil compaction zones, combined with the

2912 use of the Sesbania spp. summer green manure crop

2913 and chicken manure to try to rapidly enhance the

2914 extremely low level of soil organic matter content.

2915 This trial shows therefore the benefits of deep

2916 chiseling (about 50–70 cm chisel depth, with shanks

2917 50 cm apart) and of using organic matter (green and

2918 chicken manure).

2919 As can be seen in Fig. 5, almost as much progress

2920 in improving wheat yield potential—after 26 years of

2921crop breeding, ensued by improving crop manage-

2922ment as occurred by 26 years of breeding. In

2923addition, two other factors are apparent. Firstly, the

2924linear slopes were different (36 kg ha-1 year-1 for

2925normal trial management versus 52 kg ha-1 year-1

2926for the improved trial management) and the estimated

2927annual rate of yield increase was different (0.52%

2928year-1 for normal trial management versus

29290.68% year-1 for the improved trial management.

2930Secondly, one can observe the contrasting interacting

2931yield performance of the cultivars developed between

29321981 and 1987. For the normal trial management,

2933yields went down for these cultivars whereas for the

2934improved trial management they went up, which

2935could indicate the need for improving phenotyping

2936for yield potential and the appropriate crop manage-

2937ment practices for station field testing.

2938Wheat global partnership network builds national

2939capacity through human resources development

2940More than 40 years history of international wheat

2941nursery trials, underpinning the voluntary collabora-

2942tion of primarily public wheat improvement

2943institutions, has been accompanied in parallel by

2944intensive capacity-building efforts. More than 2000

Comparison of the yield performance of a historical set of cultivars for the

normal CIMMYT, irrigated yield trial management in Obregon in 1988 versus

agronomically improved trial management

5000

5500

6000

6500

7000

7500

8000

8500

9000

1962 1964 1967 1973 1976 1980 1982 1986

Year of Cultivar Release

Yie

ld (

kg

/ha

)

Normal CIMMYT Yield Trial Management in 1988

Agronomically Improved Yield Trial Management

Linear (Agronomically Improved Yield Trial Management)

Linear (Normal CIMMYT Yield Trial Management in 1988)

Fig. 5 Wheat grain yieldusing normal andagronomically improvedyield trial management(Obregon, Mexico, 1987–1988)


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OOF2945 scientists and research technicians from developing

2946 countries have participated in CIMMYT’s in long

2947 term hands-on courses organized in research stations

2948 in Mexico and a similar number of visiting scientists

2949 have come to CIMMYT to work shoulder to shoulder

2950 with CIMMYT scientists in the research and farmers

2951 fields, laboratories, and in the genebank (Table 12).

2952 Several hundreds of graduate students also had

2953 opportunity to conduct their thesis research with

2954 financial or technical support from CIMMYT. A

2955 number of short term special courses have been

2956 organized annually in collaborating countries partic-

2957 ularly since the 1980s.

2958 Recently however, there has been increasing con-

2959 cern globally about who will prepare the crop breeders

2960 of the twenty first Century as the number of public

2961 breeders, who produce new cultivars, is steadily

2962 declining. This pattern is not limited to the developed

2963 world, but has been reported from many developing

2964 countries as well (Guimaraes et al. 2006a, b, 2007).

2965 The genetic enhancement of wheat is not an

2966 exception, but maybe a more difficult case. Wheat

2967 breeding remains primarily in the domain of the

2968 public sector. Skilled wheat breeders in developing

2969 countries prepared in 1960s and 1970s are now either

2970 retiring or have been promoted to higher administra-

2971 tive positions in their institutions and are not actively

2972 in charge of active breeding programs. They are

2973 being replaced by scientists involved in more basic

2974 genetic studies, with less field experience. This shift

2975 is fueled by the perception that private-sector breed-

2976 ing efforts are adequate to meet cultivar needs. Also

2977 cuts in university resources have led to reduced

2978 support of field programs, and this has pushed the

2979 current public plant breeders to shift their activities

2980 toward fundamental or basic studies that can be

2981 supported by federal grants and the private sector.

2982 The loss of plant breeding programs is of great

2983 concern to both the USA plant breeding industry and

2984 the international community (Hancock 2006).

2985Furthermore, an effective and close partnership

2986with national researchers remains as one of the major

2987challenges to the successful mission of international

2988crop breeding. Their resources have been diminishing

2989in terms of human and infrastructural capital to

2990enable this to occur. However, some national partners

2991have strengthened their research capacity signifi-

2992cantly (e.g. Brazil, China, India, Mexico, South

2993Africa) over the past 40 years and their needs for

2994capacity building are less, and they work more in

2995equal partnership with the international breeding

2996programs. Hence, one of the overriding challenges for

2997many national partners will be to include in their

2998national institutional frameworks, investments in

2999research-for-development to ensure that the level of

3000science and resources are enough to provide basic

3001support and allow key outputs to be achieved. It is

3002clear that without sufficient national capacity the use

3003of international public goods produced in partnership

3004with international breeding programs, such as CI-

3005MMYT, will be restricted, and the mission therefore

3006compromised.

3007In order to develop the strategies to prevent further

3008erosion of institutional plant breeding training capac-

3009ity, several broadly attended meetings have been

3010conducted recently. Based on its broad scale study of

3011national capacities in plant breeding, the United

3012Nations of the Food and Agriculture Organization

3013(FAO) launched the Global Partnership Initiative for

3014Plant Breeding Capacity Building in 2006. In accor-

3015dance with its strategy and in order to address the

3016above described tendency, CIMMYT will continu-

3017ously support capacity-building of wheat scientists in

3018NARS through manifold ways—basic and advanced

3019courses on wheat improvement, visiting scientist

3020stays, and the support of degree thesis research.

3021Outlook: seeding innovations … nourishing hope

3022These are some of the issues that research managers

3023and wheat scientists must now confront in order to

3024select an optimal portfolio of strategic wheat genetic

3025enhancement research for the coming years, which

3026will have an impact on the ground during the coming

3027decades. Until the dramatic expansion of demand for

3028maize biofuels and the weather-induced supply

3029problems in the past few years, the prospects for a

3030reversal of the steady fall of the real prices of cereals

Table 12 Number of benefitting countries, long-term grouptrainees and visiting researchers on wheat improvement atCIMMYT

Region Countryof origin

Grouptrainees

Visitingresearchers

Developing world 85 995 1,391

Developed world 30 39 608


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3031 including wheat appeared poor. Recent projections

3032 suggest a long-term increase in the real price of wheat

3033 along with other cereals (von Braun 2007). There are

3034 a number of trends and predicted key factors on

3035 which to base decisions: for example, the growing

3036 world population needs more food, more energy, and

3037 more feed grain to supply an ever increasing global

3038 demand for animal products; decreasing water sup-

3039 plies for agriculture and the effects of climate change

3040 are increasing the levels of abiotic stress across major

3041 wheat-producing areas; the application of biotech-

3042 nologies for better use of wheat genetic resources in

3043 the betterment of the crop is likely to offer new

3044 opportunities to increase yield, providing the private

3045 sector is also sufficiently engaged.

3046 As shown by this article, CIMMYT and research

3047 partners worldwide are conserving the wheat genetic

3048 endowment and improving crop yields and stability

3049 across the major cropping systems where wheat

3050 thrives. Likewise, this manuscript illustrates how

3051 such genetic resources are addressing new global

3052 challenges to both wheat production and demand,

3053 especially for the still growing population of the

3054 developing world. Surely, the wealth of genetic

3055 resources available in the wheat gene pools (includ-

3056 ing wild species) will be among the important sources

3057 available to plant breeders in their quest for high and

3058 stable yielding wheat cultivars that meet the end use

3059 quality demands at a time of limited resources and

3060 global warming.

3061 Acknowledgement The authors thank Ms. Allison Gillies3062 (CIMMYT, Mexico) for editing an early version of this3063 manuscript. We acknowledge the kind support of the CGIAR3064 members for wheat improvement at CIMMYT through3065 unrestricted funding and other resources brought by special3066 project grants in recent years from Australia, Belgium, Bill &3067 Melinda Gates Foundation, Canada, China, Denmark,3068 European Commission, FAO, FONTAGRO, Generation3069 Challenge Program, Germany, HarvestPlus, India, Iran, Italy,3070 Japan, Mexico, Norway, Republic of Korea, Rockefeller3071 Foundation, Sasakawa Africa Association, Spain, Sweden,3072 Turkey, United Kingdom, United States of America and the3073 World Bank, as well as the in-kind contributions of national3074 partners elsewhere.

3075 References

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https://www.researchgate.net/publication/284048479_Wild_wheats_a_monograph_of_Aegilops_L?el=1_x_8&enrichId=rgreq-b97bd0b2e59dcb0078850802c561253d-XXX&enrichSource=Y292ZXJQYWdlOzIyNTgyMDgyMztBUzoxMDQxNTU1MzY0MjkwNzFAMTQwMTg0NDAyMzQ3Nw==

https://www.researchgate.net/publication/284048479_Wild_wheats_a_monograph_of_Aegilops_L?el=1_x_8&enrichId=rgreq-b97bd0b2e59dcb0078850802c561253d-XXX&enrichSource=Y292ZXJQYWdlOzIyNTgyMDgyMztBUzoxMDQxNTU1MzY0MjkwNzFAMTQwMTg0NDAyMzQ3Nw==

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https://www.researchgate.net/publication/226810273_Bringing_wild_relatives_back_into_the_family_Recovering_genetic_diversity_in_CIMMYT_improved_wheat_germplasm?el=1_x_8&enrichId=rgreq-b97bd0b2e59dcb0078850802c561253d-XXX&enrichSource=Y292ZXJQYWdlOzIyNTgyMDgyMztBUzoxMDQxNTU1MzY0MjkwNzFAMTQwMTg0NDAyMzQ3Nw==












Wheat genetic resources enhancement by the International Maize and Wheat Improvement Center (CIMMYT

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