A major terminal drought tolerance QTL of pearl milletis also associated with reduced salt uptake and enhancedgrowth under salt stress

Parbodh C. Sharma • Deepmala Sehgal •

Dhananjay Singh • Gurbachan Singh •

Rattan S. Yadav

Received: 16 December 2009 / Accepted: 24 February 2010 / Published online: 13 March 2010

� Springer Science+Business Media B.V. 2010

Abstract The performance of a major quantitative

trait locus (QTL) of terminal drought tolerance (DT)

of pearl millet was assessed under salt stress. The

test-cross hybrids of the QTL donor parent (drought

tolerant, PRLT 2/89-33), QTL recipient parent

(drought sensitive, H 77/833-2), and a set of six near

isogenic lines introgressed with a terminal DT-QTL

(QTL-NILs) were evaluated for germination and

seedling emergence at 7 days after sowing (DAS) in

Petri plates at four salinity levels, and at vegetative

(24 DAS) and maturity stages at three salinity and

alkalinity levels. Na? and K? accumulation, their

compartmentation in different plant parts, and their

effects on growth and yield parameters were evalu-

ated. The DT-QTL donor parent and QTL-NILs

accumulated less Na? in shoot parts at seedling,

vegetative and maturity stages, and also partitioned

the accumulated Na? more into nodes and internodes

and less into leaves than the drought-sensitive

recurrent parent. The pattern of reduced salt accu-

mulation in the drought-tolerant parent and QTL-

NILs was consistently associated with better growth

and productivity in saline and alkaline treatments. It

is concluded that the DT-QTL contributed by PRLT

2/89-33 exerted favourable effects on growth and

productivity traits under salt stress by limiting Na?

accumulation in leaves.

Keywords Pearl millet � Drought and salt

tolerance � Terminal drought tolerance QTL �QTL-NILs � Growth under salt stress �Ionic accumulation and compartmentation

Abbreviations

DAS Days after sowing

DT-QTL Drought tolerance QTL

DT-QTL-NILs DT-QTL-near isogenic lines

ECiw Electrical conductivity of the

irrigation water

GCA General combining ability

MABC Marker-assisted backcrossing

Introduction

Pearl millet (Pennisetum glaucum L. Br.) is an annual

diploid crop belonging to the Poaceae. Globally, it is

the seventh most important cereal crop and provides

food security to 500 million of the poorest people

living predominantly in parts of Asia and Africa.

Among the cereals, it is considered the hardiest crop,

which is grown in outlying areas peripheral to the

major production areas where crops like sorghum and

P. C. Sharma � D. Singh � G. Singh

Central Soil Salinity Research Institute (CSSRI),

Karnal, Haryana 132001, India

D. Sehgal � R. S. Yadav (&)

Institute of Biological, Environmental & Rural Sciences

(IBERS), Aberystwyth University, Gogerddan,

Aberystwyth SY23 3EB, UK

e-mail: rsy@aber.ac.uk

123

Mol Breeding (2011) 27:207–222

DOI 10.1007/s11032-010-9423-3

maize fail to produce. In the hottest and driest parts of

arid and semi-arid tropics, it is mainly grown as a

rainfed crop where yearly variations in its productiv-

ity may be ascribed to climatic variations such as

severe droughts and untimely monsoonal rains during

the cropping season. Besides drought, the crop also

suffers from the problem of excessive salts that are

present in the soil or are added by poor-quality

irrigation water. Improved adaptation to dual stresses

of water and salt is thus a desirable trait to

incorporate in pearl millet cultivars.

Recent genetic mapping research in pearl millet has

defined a number of quantitative trait loci (QTL) for

components of grain and stover yield, and for yield

maintenance under terminal drought stress conditions.

Most importantly, a major QTL associated with grain

yield per se and for drought tolerance of grain yield

has been identified on linkage group (LG) 2 which

accounted up to 32% of the phenotypic variation of

grain yield in the mapping populations (Bidinger et al.

2007; Yadav et al. 2002, 2004). The effects of this

QTL have been validated in two independent marker-

assisted backcrossing programs in which the 30%

improvement in grain yield general combining ability

(GCA) expected of this QTL under terminal drought

stress conditions was recovered in introgression lines

based on the QTL (Serraj et al. 2005).

Exposure of crop plants to drought or salt stress

triggers many similar reactions. For example, both

stresses lead to cellular dehydration, which causes

osmotic stress and removal of water from the cyto-

plasm into the extracellular space, resulting in reduc-

tion of the cytosolic and vacuolar volumes (Munns

2002; Munns and Richards 2007; Zhu 2002). Recent

investigations in Arabidopsis and rice indicate that

responses to cold, drought and salt stress are controlled

by common and conserved regulatory pathways

(Kreps et al. 2002; Rabbani et al. 2003; Seki et al.

2002; Yamaguchi-Shinozaki and Shinozaki 2006)

and, therefore, provide the prospect that QTL/gene(s)

might have a pleiotropic effect on multiple stress

tolerance. The present study was, therefore, aimed at

examining whether a drought tolerance QTL in pearl

millet would have a pleiotropic effect on salt tolerance.

To test this hypothesis, the performance of a set of near

isogenic lines introgressed with a terminal drought

tolerance QTL (QTL-NILs) was tested under a range

of salinity and alkalinity treatments. The results of the

present study will inform deployment of this drought

tolerance QTL into pearl millet cultivars that are high-

yielding and grown in the areas where twin problem of

salinity and drought are common.

Materials and methods

Plant material

Test-cross hybrids of two parental genotypes [PRLT 2/

89-33 (drought-tolerant, donor parent for drought

tolerance QTL) and H 77/833-2 (drought-sensitive,

recipient parent for drought tolerance QTL)] and a set

of six genotypes (ICMR 01029, ICMR 01031, ICMR

01040, ICMR 01046, ICMR 02042 and ICMR 02044)

introgressed with a terminal drought tolerance QTL

(QTL-NILs) were selected for this study. The devel-

opment of QTL-NILs as well as details of F1 hybrid

seed produced on these lines, and on parental geno-

types, is described in Serraj et al. (2005). Briefly, the

genomic interval on LG 2 conferring drought tolerance

(Bidinger et al. 2007; Yadav et al. 2002, 2004) was

transferred from PRLT 2/89-33 (derived from the

Iniadi landrace material from Togo and Ghana and

known for its better grain-filling ability under terminal

drought stress conditions) to the genetic background of

H 77/833-2 (widely cultivated in the Thar desert

margins of north-western India and male parent of a

number of thermotolerant, extra-early, high-tillering

and high-yielding pearl millet hybrids) following four

generations of marker-assisted backcrossing (MABC).

At each backcross, the presence or absence of the

terminal drought tolerance QTL region was deter-

mined using molecular markers bracketing the drought

tolerance QTL interval on LG 2. After four generations

of MABC, two generations of selfing was done and

marker-assisted selection was performed to generate

QTL-NILs. These QTL-NILs were similar to the

recurrent parent (H 77/833-2) except for the drought

tolerance QTL interval on LG 2 transferred from the

donor parent PRLT 2/89-33. Test-cross hybrids were

produced for each of these six QTL-NILs (ICMR

01029 to ICMR 01044), as well as onto the two

parental lines (H 77/833-2 and PRLT 2/89-33), by

using each of these lines as a pollinator onto a common

male sterile line (female parent 843A). Performances

of the eight hybrids so produced were evaluated under

controlled saline and alkaline conditions. The test-

cross hybrids involving ICMR 01029, ICMR 01031

208 Mol Breeding (2011) 27:207–222

123

and ICMR 02041 were previously found to be superior

for their yield under terminal drought tolerance,

whereas ICMR 02042 and 02044 had a yield response

in the field similar to the test-cross hybrid of the

sensitive parent H 77/833-2 (Serraj et al. 2005).

Plant growth and exposure to salt stress

Test-cross hybrids of six QTL-NILs and two parental

genotypes were evaluated for their salt tolerance

under solution culture in Petri plates, and sand culture

in pots, as well as in soil in microplots. In Petri plates,

germination and seedling emergence at 7 days after

sowing (DAS) in saline solution was evaluated.

Under sand (salinity stress) and soil (alkali stress)

culture, the performance was evaluated at vegetative

(24 DAS) and maturity (at harvest) stages. The Petri

plate experiment was conducted in a growth chamber

while the sand and soil culture experiments were

conducted in a net house at the Central Soil Salinity

Research Institute (CSSRI), Karnal, Haryana, India,

from June to September, 2008, when natural growing

conditions (temperature 25–35�C, relative humidity

60–82%) are generally favourable for pearl millet.

Petri plate germination and seedling emergence

experiment

Germination and seedling emergence was studied in

Petri plates at four salinity levels (electrical conduc-

tivity of the irrigation water [Eciw] 15, 18, 22 and

26 dS m-1) and control (� strength Hoagland solu-

tion) in four replications at 25�C in a growth

chamber. Twenty-five uniform seeds were placed in

each Petri plate, lined with Whatman filter paper (no.

41), with the addition of 10 ml Hoagland saline

solution. Data on seed germination (measured as

protrusion of 2 mm radical) and seedling emergence

(measured as emergence of pair of first leaves)

percentage was recorded at 24 h intervals over 7

DAS. The saline water for irrigation was prepared by

adding NaCl, Na2SO4 and CaCl2, keeping the Na:Ca

and Cl:SO4 ratio of 4:1 in � strength Hoagland

nutrient solution using distilled water. Shoots of

7-day-old seedlings were separated from roots and

their Na? and K? contents determined by extraction

in 100 mM acetic acid for 2 h at 90�C as described in

Flowers and Yeo (1981).

Sand culture salinity experiment in pots

For studying plant responses at vegetative (24 DAS)

and maturity stages under saline conditions, hybrids

were evaluated with saline irrigation (ECiw 9 and

12 dS m-1) together with the control (� strength

Hoagland solution, ECiw 2 dS m-1) treatment in

ceramic pots of 20 kg capacity filled with sand. The

saline irrigation waters were prepared as described in

the previous section using normal tap water. The

salinity levels for each treatment were maintained in

each pot throughout the experiment by flushing

treatments at appropriate intervals (Sharma and Gill

1992). Fifteen seeds per pot were sown in four

replications. Each pot was thinned to five seedlings at

15 DAS. Two seedlings from each pot were harvested

at 24 DAS. Roots and shoots of these seedlings were

separated for recording fresh and dry weight and for

ionic analysis. The remaining three plants per pot

were grown until maturity. At maturity, these three

plants per pot were harvested and air dried to record

their biomass, stover and grain yield as detailed in

Yadav et al. (2002). Further, the main shoot of each

plant was separated into leaves, nodes and internodes

for ionic analysis using flame spectrophotometery.

Na? and K? contents were determined by wet

digestion method using flame spectrophotometery as

described in Sharma and Kumar (1999).

Soil culture alkalinity experiment in micro plots

In this experiment, the same set of eight pearl millet

hybrids was evaluated under alkali stress in micro

plots (6 9 4 m) filled with two levels of alkali soils

(pH 9.0 and 9.4) as well as reclaimed alkali soil (pH

8.5, used as control), in three replications. The

alkalinity levels were prepared by spraying required

amounts of Na2CO3 and NaHCO3 in different layers

of soil (15 cm each), which were then mixed

thoroughly before filling in micro plots (1 m deep).

Each replication comprised ten plants per row. At 24

DAS, two plants were sampled from each entry

across three replications and their shoot and root fresh

and dry weights and ionic accumulation determined

as described in the previous section. Eight plants per

row were harvested at maturity for recording dry

weight of stover, ear-heads, and grain. Extracts of the

plants harvested at 24 DAS, and at maturity, were

Mol Breeding (2011) 27:207–222 209

123

also subjected to ionic analysis using flame spectro-

photometery.

Statistical analysis

Statistical analysis and analysis of variance was con-

ducted using the statistical program package Indo-Stat

2007. Data were analyzed using salinity, alkalinity and

genotypes as main effects. Genotype 9 salinity and

genotype 9 alkalinity interactions were calculated sep-

arately for salinity and alkalinity experiments.

Results

Analysis of variance conducted on data recorded at

seedling and maturity stages is presented in Tables 1,

2, 3, 4, 5. Salinity and alkalinity stresses significantly

Table 1 Shoot and root dry weight (g per plant) at 24 DAS in hybrids of parental genotypes, and of QTL-NILs, at three salinity and

alkalinity levels

Genotypes Catalogue no. Salinity stress Alkalinity stress

Shoot dry

weight

Root dry

weight

Shoot dry

weight

Root dry

weight

ECiw 2 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 3.14f 0.38ef 1.00l 0.12i

Drought-tolerant parent 843A 9 PRLT 2/89-33 1.85cde 0.15ab 1.05l 0.08h

QTL-NILs 843A 9 ICMR 01029 2.88f 0.34cef 0.98l 0.11i

843A 9 ICMR 01031 2.71ef 0.43f 0.24cdefgh 0.05def

843A 9 ICMR 01040 2.53ef 0.40f 0.15a 0.03abcd

843A 9 ICMR 01046 3.22f 0.38ef 0.17a 0.02abc

843A 9 ICMR 02042 2.64ef 0.33cef 0.44jk 0.06efg

843A 9 ICMR 02044 2.33def 0.17abc 0.39gij 0.07gh

ECiw 9 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 1.21abc 0.12ab 0.08abc 0.01a

Drought-tolerant parent 843A 9 PRLT 2/89-33 0.95abc 0.17ab 0.58k 0.06efg

QTL-NILs 843A 9 ICMR 01029 1.26bc 0.12ab 0.19bcde 0.03abcd

843A 9 ICMR 01031 1.25bc 0.16ab 0.14abcd 0.01ab

843A 9 ICMR 01040 1.51bcd 0.16ab 0.22cde 0.03abcd

843A 9 ICMR 01046 1.11abc 0.15ab 0.24cdefg 0.04cde

843A 9 ICMR 02042 1.84cde 0.23bcde 0.39fghij 0.06gh

843A 9 ICMR 02044 1.54bcd 0.13ab 0.35efghij 0.07fgh

ECiw 12 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 0.29a 0.03a 0.05ab 0.01bcd

Drought-tolerant parent 843A 9 PRLT 2/89-33 1.03abc 0.12ab 0.15abcd 0.02ab

QTL-NILs 843A 9 ICMR 01029 1.48bcd 0.16ab 0.23cdefg 0.02abcd

843A 9 ICMR 01031 0.79ab 0.18abcd 0.15bcde 0.03abcd

843A 9 ICMR 01040 1.29bc 0.18abcd 0.21defghi 0.02abc

843A 9 ICMR 01046 0.78ab 0.10ab 0.15cdef 0.02ab

843A 9 ICMR 02042 0.82ab 0.08ab 0.08abcd 0.02abcd

843A 9 ICMR 02044 0.78ab 0.15ab 0.20bcde 0.02ab

LSD (P = 0.05)

Genotypes (G) 0.34* NS 0.07*** 0.01***

Salinity (S) 0.28*** 0.05*** 0.05*** 0.01***

G 9 S NS NS 0.14*** 0.02***

Means within a column that do not have a common letter are significantly different by LSD0.05 test

210 Mol Breeding (2011) 27:207–222

123

affected all the traits evaluated in this study. The two

parents and six QTL-NILs were not significantly

different for root dry weight at the seedling stage and

for shoot dry weight at maturity harvest under salinity

stress but were significantly different for the rest of

the traits evaluated under salinity and alkalinity stress

conditions. Genotypes 9 salinity treatments (G 9 S)

interactions were significant for all traits except for

shoot and root dry weight at 24 DAS, grain yield at

maturity, and concentration of Na? and K? ion in

roots, internodes and leaves at maturity. Geno-

types 9 alkalinity treatments (G 9 A) interactions

were significant for all traits but at a lower level of

significance (P = 0.05) for grain yield and biomass

yield. These data indicated that salinity and alkali

levels chosen for this study were appropriate for

expression of genotypic differences in parents and

QTL-NILs.

Table 2 Growth, and yield parameters measured at maturity stage in hybrids of parental genotypes and of QTL-NILs, at three

salinity levels

Genotypes Catalogue no. Biomass

yield (g per pot)

Stover

yield (g per pot)

Root dry

weight (g per pot)

Grain

yield (g per pot)

ECiw 2 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 351i 169i 105j 119d

Drought-tolerant parent 843A 9 PRLT 2/89-33 249efg 145gh 41ef 75abc

QTL-NILs 843A 9 ICMR 01029 316h 159hi 68i 107d

843A 9 ICMR 01031 320hi 157hi 52h 109d

843A 9 ICMR 01040 346i 171i 49gh 101cd

843A 9 ICMR 01046 271g 154h 43fg 71ab

843A 9 ICMR 02042 298h 146gh 48gh 101cd

843A 9 ICMR 02044 253fg 135fg 41ef 81bc

ECiw 9 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 210cd 100abcd 36cde 71ab

Drought-tolerant parent 843A 9 PRLT 2/89-33 225def 115de 33bcd 81bc

QTL-NILs 843A 9 ICMR 01029 249efg 128ef 48gh 78abc

843A 9 ICMR 01031 222de 111bcd 36de 81bc

843A 9 ICMR 01040 211cd 101abcd 34bcd 78abc

843A 9 ICMR 01046 176ab 100abcd 35bcd 53a

843A 9 ICMR 02042 212cd 113cd 36cde 79abc

843A 9 ICMR 02044 205bcd 115de 33bcd 64ab

ECiw 12 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 195abcd 95a 34bcd 72ab

Drought-tolerant parent 843A 9 PRLT 2/89-33 209cd 107abcd 32bcd 62ab

QTL-NILs 843A 9 ICMR 01029 194abcd 99abc 32bcd 67ab

843A 9 ICMR 01031 173a 94a 27a 57ab

843A 9 ICMR 01040 188abc 98abc 36cde 64ab

843A 9 ICMR 01046 176ab 95ab 31abcd 57ab

843A 9 ICMR 02042 184abc 93a 30abc 68ab

843A 9 ICMR 02044 195abcd 104abcd 30ab 66ab

LSD (P = 0.05)

Genotypes (G) 19*** NS 3*** 12***

Salinity (S) 9*** 5*** 2*** 8***

G 9 S 26*** 13*** 5*** NS

Means within a column that do not have a common letter are significantly different by LSD0.05 test

Mol Breeding (2011) 27:207–222 211

123

Growth and ionic accumulation at seedling

and vegetative stage

Seedling stage (7 DAS)

Germination as well as seedling emergence declined

with increase in salinity in all the eight test-cross hybrids

evaluated. At ECiw 26 dS m-1, seedling germination

declined by 60% in the drought-sensitive recurrent

parent H 77/833-2 and 40% in the hybrid of the drought-

tolerant parent PRLT 2/89-33 compared to control

treatment (data not shown). Mean seedling emergence

across hybrids declined by 19 and 66% at ECiw

15 dS m-1 and ECiw 26 dS m-1, respectively, in the

Petri plate experiment, compared to control (Fig. 1A).

At the highest salinity level of ECiw 26 dS m-1, an 80%

reduction in seedling emergence was recorded in the

hybrid of the drought-sensitive recurrent parent H 77/

Table 3 Growth and yield parameters measured at maturity stage in hybrids of parental genotypes and of QTL-NILs, at three

alkalinity levels

Genotypes Catalogue no. Biomass

yield (g per row)

Stover

yield (g per row)

Grain

yield (g per row)

pH 8.5

Drought-sensitive parent 843A 9 H 77/833-2 838i 418f 297j

Drought-tolerant parent 843A 9 PRLT 2/89-33 813hi 395f 311j

QTL-NILs 843A 9 ICMR 01029 689gh 365f 204fgh

843A 9 ICMR 01031 733hi 395f 237ghij

843A 9 ICMR 01040 606fg 297e 219fgh

843A 9 ICMR 01046 784hi 389f 294ij

843A 9 ICMR 02042 736hi 369f 275hij

843A 9 ICMR 02044 800hi 410f 304j

pH 9.0

Drought-sensitive parent 843A 9 H 77/833-2 435cde 171bc 194efg

Drought-tolerant parent 843A 9 PRLT 2/89-33 524ef 216cd 223fghi

QTL-NILs 843A 9 ICMR 01029 506def 232d 187defg

843A 9 ICMR 01031 348bc 147b 128bcde

843A 9 ICMR 01040 388cd 165b 153cdef

843A 9 ICMR 01046 337bc 144b 115abcd

843A 9 ICMR 02042 486de 216cd 189defg

843A 9 ICMR 02044 403cde 167b 158cdef

pH 9.4

Drought-sensitive parent 843A 9 H 77/833-2 125a 36a 42a

Drought-tolerant parent 843A 9 PRLT 2/89-33 219a 78a 79ab

QTL-NILs 843A 9 ICMR 01029 253ab 84a 99abc

843A 9 ICMR 01031 184a 65a 63ab

843A 9 ICMR 01040 178a 57a 63ab

843A 9 ICMR 01046 153a 57a 50a

843A 9 ICMR 02042 172a 59a 53ab

843A 9 ICMR 02044 165a 60a 54ab

LSD (P = 0.05)

Genotypes (G) 57*** 24*** 31***

Alkalinity (A) 40*** 16*** 23***

G 9 A 111* 44*** 6*

Means within a column that do not have a common letter are significantly different by LSD0.05 test

212 Mol Breeding (2011) 27:207–222

123

833-2, compared to 50% in the drought-tolerant parent

PRLT 2/89-33. Similarly, most QTL-NILs (except for

ICMR 01046 and ICMR 02042) showed lower reduc-

tions in seedling emergence compared to the drought-

sensitive parent H 77/833-2, largely on the pattern of the

drought-tolerant parent PRLT 2/89-33.

Na?/K? ratios (on a molar basis) in shoots were

higher in the sensitive parent H 77/833-2 and lower in

the tolerant parent PRLT 2/89-33 and QTL-NILs

(Fig. 1B).

Vegetative stage (24 DAS)

Shoot and root dry weights of seedlings at 24 DAS

for the two parents and six QTL-NILs under different

salinity and alkalinity stress levels are given in

Table 1. In the control treatment of the sand-culture

experiment (ECiw 2.0 dS m-1), the drought-sensitive

parent (H 77/833-2) produced greater shoot dry

weight compared to the drought-tolerant parent

(PRLT 2/89-33). More specifically, the shoot dry

Table 4 Na/K ratio in plant tissues of parental genotypes, and in QTL-NILs, at three salinity levels at harvest stage

Genotypes Catalogue no. Na/K

Node Internode Leaf Root

ECiw 2 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 0.13ab 0.12a 0.10a 0.56a

Drought-tolerant parent 843A 9 PRLT 2/89-33 0.13ab 0.10a 0.12a 0.38a

QTL-NILs 843A 9 ICMR 01029 0.19b 0.13a 0.12a 0.56a

843A 9 ICMR 01031 0.12ab 0.13a 0.13ab 0.52a

843A 9 ICMR 01040 0.11a 0.12a 0.10a 0.42a

843A 9 ICMR 01046 0.12ab 0.13a 0.14abc 0.42a

843A 9 ICMR 02042 0.14ab 0.12a 0.10a 0.44a

843A 9 ICMR 02044 0.12ab 0.11a 0.10a 0.48a

ECiw 9 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 0.79h 0.48i 0.56jk 2.66b

Drought-tolerant parent 843A 9 PRLT 2/89-33 0.38c 0.23b 0.22def 2.65b

QTL-NILs 843A 9 ICMR 01029 0.46de 0.40fg 0.25ef 2.50b

843A 9 ICMR 01031 0.58f 0.35cde 0.29fg 2.70b

843A 9 ICMR 01040 0.46de 0.22b 0.19bcde 2.56b

843A 9 ICMR 01046 0.40cd 0.26b 0.20cde 2.60b

843A 9 ICMR 02042 0.50e 0.37def 0.22de 2.67b

843A 9 ICMR 02044 0.47de 0.39ef 0.16abcd 2.87b

ECiw 12 dS m-1

Drought-sensitive parent 843A 9 H 77/833-2 0.81h 0.47i 0.62kl 5.17f

Drought-tolerant parent 843A 9 PRLT 2/89-33 0.75h 0.34cd 0.32gh 3.30c

QTL-NILs 843A 9 ICMR 01029 0.38c 0.45hi 0.37hi 3.50cd

843A 9 ICMR 01031 0.43cde 0.41fgh 0.62kl 3.86d

843A 9 ICMR 01040 0.47de 0.31c 0.44i 3.68cd

843A 9 ICMR 01046 0.64fg 0.44ghi 0.64l 3.76d

843A 9 ICMR 02042 0.66g 0.44ghi 0.53j 3.62cd

843A 9 ICMR 02044 0.78h 0.62j 0.37hi 4.63e

LSD (P = 0.05)

Genotypes (G) 0.07*** 0.06*** 0.07*** 0.28***

Salinity (S) 0.04*** 0.03*** 0.04*** 0.21***

G 9 S 0.12*** 0.08*** 0.11*** 0.61**

Means within a column that do not have a common letter are significantly different by LSD0.05 test

Mol Breeding (2011) 27:207–222 213

123

weight of the drought-sensitive parent (H 77/833-2)

was 1.7 and 1.3 times higher than that of the drought-

tolerant parent (PRLT 2/89-33) in the control treat-

ment and salinity treatment of ECiw 9 dS m-1.

However, in the salinity treatment of ECiw

12 dS m-1, the trend was opposite. In this treatment,

the hybrid of the drought-tolerant parent (PRLT 2/89-

33) produced much greater shoot dry weight (3.5

times) than the sensitive-parent (H 77/833-2). Fur-

thermore, the QTL-NILs also produced much greater

shoot dry weight (3.3 times on average) compared to

the drought-sensitive parent at this salinity treatment

of ECiw 12 dS m-1. Among the QTL-NILs, ICMR

01029 and ICMR 01040 produced the highest shoot

dry weight at 24 DAS, even higher than the drought-

tolerant parent PRLT 2/89-33, at the highest salinity

level of ECiw 12 dS m-1. The maximum decline

(90% compared to controls) in shoot dry weight was

recorded in the drought-sensitive parent H 77/833-2

at this salinity treatment of ECiw 12 dS m-1. At

Table 5 Na/K ratio in plant tissues of parental genotypes, and in QTL-NILs, at three alkalinity levels at maturity stage

Genotypes Catalogue no. Na/K

Node Internode Leaf

pH 8.5

Drought-sensitive parent 843A 9 H 77/833-2 0.26a 0.25ab 0.47de

Drought-tolerant parent 843A 9 PRLT 2/89-33 0.31a 0.13a 0.26ab

QTL-NILs 843A 9 ICMR 01029 0.35a 0.26ab 0.25a

843A 9 ICMR 01031 0.26a 0.34ab 0.35abc

843A 9 ICMR 01040 0.32a 0.31ab 0.28ab

843A 9 ICMR 01046 0.28a 0.25ab 0.27ab

843A 9 ICMR 02042 0.40a 0.38b 0.24a

843A 9 ICMR 02044 0.35a 0.28ab 0.27ab

pH 9.0

Drought-sensitive parent 843A 9 H 77/833-2 2.62efg 1.34ef 0.96jk

Drought-tolerant parent 843A 9 PRLT 2/89-33 1.88c 0.44b 0.62fg

QTL-NILs 843A 9 ICMR 01029 2.21cde 1.14de 0.68gh

843A 9 ICMR 01031 2.71fgh 2.35h 0.67gh

843A 9 ICMR 01040 1.28b 0.75c 0.37bcd

843A 9 ICMR 01046 2.03cd 2.01g 0.60fg

843A 9 ICMR 02042 3.14hij 1.95g 0.37bcd

843A 9 ICMR 02044 2.38def 2.09g 0.40cd

pH 9.4

Drought-sensitive parent 843A 9 H 77/833-2 0.81m 3.73l 1.88l

Drought-tolerant parent 843A 9 PRLT 2/89-33 0.75kl 1.03d 0.85ij

QTL-NILs 843A 9 ICMR 01029 0.38kl 3.31k 1.03k

843A 9 ICMR 01031 0.43ijk 2.94j 0.77hi

843A 9 ICMR 01040 0.47ghi 1.40f 0.55ef

843A 9 ICMR 01046 0.64jk 2.61i 0.81i

843A 9 ICMR 02042 0.66l 2.43hi 0.66fgh

843A 9 ICMR 02044 0.78hij 2.49hi 0.88ij

LSD (P = 0.05)

Genotypes (G) 0.43*** 0.20*** 0.11***

Alkalinity (A) 0.25*** 0.13*** 0.06***

G 9 A 0.71* 0.37*** 0.18***

Means within a column that do not have a common letter are significantly different by LSD0.05 test

214 Mol Breeding (2011) 27:207–222

123

ECiw 12 dS m-1, the decline in shoot dry weight in

hybrids of the drought-tolerant parent PRLT 2/89-33

and QTL-NILs (e.g. ICMR 01029 and ICMR 01040)

was much less (44–48%) compared to the drought-

sensitive parent H 77/833-2. Furthermore, under

alkali stress, the mean shoot dry weight of the eight

hybrids declined by 47 and 65% at pH 9.0 and 9.4,

respectively, compared to their control plants. No

significant differences were recorded in root dry

weight of parents and QTL-NILs in salinity treat-

ments conducted under sand culture conditions at 24

DAS.

In the alkalinity experiment, among all the geno-

types evaluated, the highest shoot (1.0 g per plant)

and root (0.12 g per plant) dry weights were recorded

in the drought-sensitive parent (H 77/833-2) under

control conditions. However, shoot and root dry

weight reductions in the drought-sensitive parent

were much greater in alkali stress treatments com-

pared to the hybrids of the drought-tolerant parent

and QTL-NILs. Compared to control conditions, the

reduction in shoot dry weight in the drought-sensitive

parent (92%) was significantly higher than of the

drought-tolerant parent (45%) at pH 9.0. Moreover, at

pH 9.0, shoot dry weight in QTL-NIL ICMR 01029

was almost three times greater than the drought-

sensitive parent H 77/833-2. No significant differ-

ences were recorded in root dry weight of parents and

QTL-NILs in salinity treatments conducted under

sand culture conditions at 24 DAS.

Growth and ionic accumulation at maturity

Stover, grain and biomass yield

Total biomass (sum total of stover and grain yield)

accumulated by the parental hybrids and QTL-NILs

in salinity and alkalinity experiments are presented in

Tables 2 and 3. Under salinity stress, plant biomass

yield averaged across all hybrids declined by about

-20

0

20

40

60

80

100

120

843AxH 77/833-2 843A x ICMR 1029 843A x ICMR 1031 843A x ICMR 1040 843A x ICMR 1046 843A x ICMR 2042 843A x ICMR 2044 843A x PRLT 2/89-33

See

dlin

g e

mer

gen

ce (

%) 2 dS/m 15 dS/m 18 dS/m 22 dS/m 26 dS/m

A

0

1

2

3

4

5

2 15 18 22 26

Na/

K in

See

dlin

g S

ho

ot

Salinity levels (ECiw, dS/m)

843AxH 77/833-2843A x ICMR 1029843A x ICMR 1031843A x ICMR 1040843A x ICMR 1046843A x ICMR 2042843A x ICMR 2044843A x PRLT 2/89-33

B

Fig. 1 Seedling emergence percentage (A) and shoot Na/K

accumulation (B) recorded at 7 DAS in test-cross hybrids of

parental genotypes (H 77/833-2, PRLT 2/89-33), and of QTL-

NILs (ICMR 01029, ICMR 01031, ICMR 1040, ICMR 1046,

ICMR 02042 and ICMR 02044) differing by a terminal

drought tolerance QTL, at five salinity levels (ECiw 2, 15,

18, 22 and 26 dS m-1)

Mol Breeding (2011) 27:207–222 215

123

28 and 36% at salinity levels of ECiw 9 and

12 dS m-1, respectively, compared to plants growing

under the control treatment (ECiw 2 dS m-1). At

ECiw 2 dS m-1, the drought-sensitive parent (H 77/

833-2) produced the highest plant biomass (350 g per

pot) whereas the drought-tolerant parent (PRLT 2/89-

33) produced the least biomass (249 g per pot). As at

the vegetative stage, this trend was reversed in the

salinity treatments of ECiw 9.0 and 12.0 dS m-1. In

both these salinity treatments, the drought-tolerant

parent (PRLT 2/89-33) produced higher biomass than

the drought-sensitive parent (H 77/833-2) (Table 2).

Moreover, compared to control experiment (ECiw

2.0 dS m-1), the percentage reduction in plant bio-

mass was minimal in the drought-tolerant parent (10

and 16% at ECiw 9 and 12 dS m-1, respectively) and

maximal in the drought-sensitive parent (40 and 44%

at ECiw 9 and 12 dS m-1, respectively). Further-

more, hybrids of QTL-NILs also showed lower

percentage reductions (19–39% at ECiw 9 dS m-1

with an average of 28.9%, and 23–45% at ECiw

12 dS m-1 with an average of 37.6%) in plant

biomass compared to the sensitive parent. At ECiw

9 dS m-1, hybrids of genotypes ICMR 01029 and

ICMR 02044 showed least reduction in biomass (21

and 19% reduction, respectively) while hybrids of

genotypes ICMR 01040 and ICMR 01046 showed

biomass reductions (39 and 35%, respectively)

closer to hybrids of the drought-sensitive parent H

77/833-2.

In the control treatment of the alkalinity experi-

ment (reclaimed alkali soils, pH 8.5), again the hybrid

of the drought-sensitive parent (H 77/833-2) pro-

duced the highest biomass (838 g per row) among all

the eight (six QTL NILs and two parents) hybrids

tested. However, in alkali treatments (pH 9.0 and

9.4), it was the drought-tolerant parent (PRLT 2/89-

33) that produced the greatest biomass yield and the

least percentage reductions (73% in PRLT 2/89-33

compared to 85% in H 77/833-2 at pH 9.4) compared

to the control treatment (Table 3). Furthermore, the

QTL-NIL ICMR 01029 produced almost double the

biomass yield at pH 9.4 compared to the drought-

sensitive parent H 77/833-2. The hybrid of QTL-NIL

ICMR 01029 also produced around 15% higher

biomass yield over the hybrid of the drought-tolerant

parent PRLT 2/89-33.

Reductions of 21 and 26% in stover yield was

recorded in the drought-tolerant parent (PRLT 2/89-

33) compared to 41 and 44% in the drought-sensitive

parent (H 77/833-2) at ECiw 9 and 12 dS m-1,

respectively (Table 2). QTL-NILs also showed less

reduction in stover yield than the drought-sensitive

parent H 77/833-2 under higher salinity treatments.

Stover yield was also significantly affected by

alkalinity and a 52% mean reduction at pH 9.0 and

83% at pH 9.4 was recorded compared to the control

treatment (pH 8.5) (Table 3). Amongst the QTL-

NILs, the best performance was observed in QTL-

NIL ICMR 01029, which showed only 36% reduction

in stover yield at pH 9.0 and 76% at pH 9.4 compared

to 59 and 91%, respectively, in the drought-sensitive

parent H 77/833-2. QTL-NILs ICMR 01040 and

ICMR 02042 also showed lower percentage reduction

in stover yield (44 and 41% at pH 9.0, respectively)

compared to control plants.

At ECiw 9 dS m-1, QTL-NIL ICMR 01029

showed a grain yield reduction of 26% compared to

the drought-sensitive parent (H 77/833-2) which

showed a 40% reduction in grain yield. Under

alkalinity stress, similar results were recorded in

plant grain yield (Table 2). Amongst the QTL-NILs,

ICMR 01046 was recorded as having the maximum

reduction of 61% in plant grain yield at pH 9.0

compared to control plants.

Ionic accumulation at maturity

Data on Na? accumulation recorded in various plant

parts (root, leaf, node, internodes) of the hybrids of

parental genotypes, and of the QTL-NILs, are

presented in Figs. 2, 3, 4. In general, nodes retained

the highest Na? concentration in the shoot of the

eight hybrids followed by roots, internodes and

leaves (Fig. 2). In the control treatments (ECiw

2 dS m-1), Na? concentration in these parts was

similar in the hybrids of the two parental genotypes.

However, at ECiw 9.0 dS m-1, the drought-sensitive

parent (H 77/833-2) accumulated almost twice

(3.06 mmol g-1 dry weight) the concentration of

Na?, considering all parts together, compared to the

drought-tolerant parent PRLT 2/89-33 (1.72 mmol

g-1 dry weight). Notably, at the highest salinity level

of ECiw 12 dS m-1, the two parental genotypes (H

77/833-2 and PRLT 2/89-33) accumulated similar

Na? concentration in roots, nodes and internodes but

in leaves the drought-tolerant parent (PRLT 2/89-33)

accumulated less than half the concentration of Na?

216 Mol Breeding (2011) 27:207–222

123

(Fig. 2) compared to the hybrid of the drought-

sensitive parent (H 77/833-2).

Accumulation of Na? in the hybrids of QTL-NILs

was essentially similar to the hybrid of the drought-

tolerant parent PRLT 2/89-33 in both saline and

alkaline treatments. In salinity treatments, the amount

of Na? increased in all shoot parts of QTL-NILs but

this increase was greater in nodes and internodes than

in leaves. At the salinity level of ECiw 9 dS m-1, the

amount of Na? in leaves of QTL-NILs was, on

average, half that in the drought-sensitive parent H

77/833-2. Further, the leaf Na? in QTL-NILs was, on

average, 3–4 times lower compared to nodes and

internodes in the drought-sensitive parent. In alkali

stress treatments, the drought-sensitive parent

accumulated double the amount of Na? in internodes

(pH 9.0 and 9.4) and leaves (pH 9.4) in comparison to

the drought-tolerant parent (Fig. 3). The increment in

Na? accumulation in nodes was similar in the two

parental genotypes even at the highest alkali level of

pH 9.4. All QTL-NILs accumulated less Na? in

leaves, invariably 3–4 times less than nodes and

internodes. Furthermore, the mean of six QTL-NILs

hybrids accumulated Na? in leaves 2.3 times less

than the drought-sensitive parent (Fig. 3) at the

highest alkali stress level of pH 9.4.

K? accumulation generally declined with increase

in salinity and alkalinity stress in all plant parts. Total

K? content was similar in hybrids of both the parental

genotypes in control conditions (ECiw 2 dS m-1, pH

0.0

0.5

1.0

1.5

843AxH 77/833-2 843A x ICMR 1029 843A x ICMR 1031 843A x ICMR 1040 843A x ICMR 1046 843A x ICMR 2042 843A x ICMR 2044 843A x PRLT 2/89-33No

de

Na

(mm

ol/g

dry

wt)

Node A

0.0

0.5

1.0

1.5

843AxH 77/833-2 843A x ICMR 1029 843A x ICMR 1031 843A x ICMR 1040 843A x ICMR 1046 843A x ICMR 2042 843A x ICMR 2044 843A x PRLT 2/89-33

Inte

rno

de

Na

(mm

ol/g

d

ry w

t)

Internode B

0.0

0.5

1.0

1.5

843AxH 77/833-2 843A x ICMR 1029 843A x ICMR 1031 843A x ICMR 1040 843A x ICMR 1046 843A x ICMR 2042 843A x ICMR 2044 843A x PRLT 2/89-33Lea

f N

a (m

mo

l/g d

ry w

t)

LeavesC

0.0

0.5

1.0

1.5

843AxH 77/833-2 843A x ICMR 1029 843A x ICMR 1031 843A x ICMR 1040 843A x ICMR 1046 843A x ICMR 2042 843A x ICMR 2044 843A x PRLT 2/89-33

Ro

ot

Na

(mm

ol/g

d

ry w

t)

2 dS/m 9 dS/m 12 dS/m RootsD

Fig. 2 Na concentration (mmol g-1 dry weight) in nodes (A),

internodes (B), leaves (C) and roots (D) of pearl millet hybrids

on parental genotypes (H 77/833-2, PRLT 2/89-33), and of

QTL-NILs (ICMR 01029, ICMR 01031, ICMR 1040, ICMR

1046, ICMR 02042 and ICMR 02044) differing by a terminal

drought tolerance QTL, at three salinity levels (ECiw 2, 9 and

12 dS m-1)

Mol Breeding (2011) 27:207–222 217

123

8.5). However, it declined sharply in hybrid of the

drought-sensitive parent H 77/833-2, both with

increase in saline or alkaline stress compared to

hybrid of the drought-tolerant parent PRLT 2/89-33

(data not given). Amongst different plant parts,

nodes (1.48 mmol g-1 dry weight) and internodes

(1.51 mmol g-1 dry weight) accumulated higher

K? under salinity stress compared to leaves

(1.30 mmol g-1 dry weight), whereas the least accu-

mulation was recorded in roots (0.45 mmol g-1 dry

weight). Moreover, the differences in K? accumula-

tion in leaves were small and were not significantly

different among the eight test-cross hybrids of parents

and QTL-NILs in salinity treatments. Furthermore,

under alkalinity stress treatment of pH 9.0 of the

drought-tolerant parent hybrid, a higher K?

concentration was recorded in nodes (0.51 mmol g-1

dry weight) and internodes (0.77 mmol g-1 dry

weight) than in the drought-sensitive parent hybrid

(0.34 and 0.62 mmol g-1 dry weight in nodes and

internodes, respectively). A similar pattern was

evident for these plant parts at higher alkali stress

level of pH 9.4. Further, the K? content declined by

52% in the drought-sensitive parent hybrid H 77/833-

2 at pH 9.4 compared to 37% in the drought-tolerant

parent hybrid PRLT 2/89-33. A lower K? content

was recorded in different plant parts of the QTL-NILs

hybrids, ICMR 01029 and ICMR 01031, compared to

the other four QTL-NILs hybrids. Notably, in both

the salinity as well as in alkalinity treatments, K?

accumulation in QTL-NILs was not different from

either parent, unlike Na? accumulation.

Fig. 3 Na concentration (mmol g-1 dry weight) in nodes (A),

internodes (B) and leaves (C) of pearl millet hybrids on

parental genotypes (H 77/833-2, PRLT 2/89-33), and of QTL-

NILs (ICMR 01029, ICMR 01031, ICMR 1040, ICMR 1046,

ICMR 02042 and ICMR 02044) differing by a terminal

drought tolerance QTL, at three alkalinity levels (pH 8.5, 9.0

and 9.4)

218 Mol Breeding (2011) 27:207–222

123

Under salinity stress, on a mean basis, the highest

Na/K ratio was recorded in roots (2.35), and was

roughly five times higher than in nodes (0.42),

internodes (0.30) and leaves (0.29) (Table 4). How-

ever, under alkali stress (Table 5), the highest Na/K

ratio was recorded in nodes (2.06) compared to

internodes (1.42) and leaves (0.60). Averaged over

different plant parts, the drought-sensitive parent (H

77/833-2) hybrid had a higher Na/K ratio (1.76) at

ECiw 12 dS m-1 compared to drought-tolerant par-

ent hybrid (1.17). The mean Na/K ratio in six QTL-

NILs hybrids was 1.33 at this salinity level. Similarly,

under alkalinity (pH 9.4), the drought-sensitive parent

(H 77/833-2) showed a higher Na/K ratio (3.37)

compared to the drought-tolerant parent (PRLT 2/89-

33) hybrid (1.84), when averaged over different plant

parts. The mean Na/K ratio in the six QTL-NILs

hybrids was 2.24 at pH 9.4. Tissue Na/K ratios in

salinity treatments were higher in all plant parts of the

drought-sensitive parent (H 77/833-2) than the

drought-tolerant parent (PRLT 2/89-33) (Fig. 4).

Further, on averaging over alkali treatments, the

hybrid of the drought-sensitive parent (H 77/833-2)

recorded a higher Na/K ratio in nodes (2.46),

internodes (1.77) and leaves (1.10) compared to the

drought-tolerant parent (PRLT 2/89-33) as well as all

the QTL-NILs. At pH 9.4, nodes of the drought-

tolerant parent hybrid showed a lower Na/K ratio

(3.66) compared to the drought-sensitive parent

hybrid (4.51), ranging from 2.93 (ICMR 1040) to

3.92 (ICMR 2042) in QTL-NILs. Further, internodes

of the drought-sensitive parent hybrid recorded more

than three times the Na/K ratio (3.73) of the drought-

tolerant parent hybrid (PRLT 2/89-33) (1.03). Among

the QTL-NILs, the Na/K ratio ranged from 1.40

(ICMR 1040) to 3.31 (ICMR 1029).

Discussion

The aim of this study was to assess the performance

of a terminal drought tolerance QTL under salt stress.

To accomplish that, we evaluated hybrids of the QTL

donor and recipient parental genotypes and QTL-

NILs to which different proportions of the drought

tolerance QTL region were introgressed from PRLT

0.0

0.2

0.4

0.6

0.8

1.0

2 9 12 2 9 12 2 9 12

Na/

K

Salinity levels (dS/m)

843A x PRLT 2/89-33

843A x H 77/833-2

QTL-NILs

Node

InternodeLeaf

A

0.0

1.0

2.0

3.0

4.0

5.0

8.5 9.0 9.4 8.5 9.0 9.4 8.5 9.0 9.4

Na/

K

Alkalinity levels (pH)

843A x PRLT 2/89-33

843A x H 77/833-2

QTL-NILsNode

InternodeLeaf

B

Fig. 4 Na/K ratio in nodes, internodes and leaves of hybrids of parental genotypes and of QTL-NILs (values presented as average of

six NILs) at three salinity (ECiw 2, 9 and 12 dS m-1) (A) and alkalinity (pH 8.5, 9.0 and 9.4) levels (B)

Mol Breeding (2011) 27:207–222 219

123

2/89-33 parent into H 77/833-2, using markers

bracketing the QTL region (Bidinger et al. 2007;

Serraj et al. 2005; Yadav et al. 2002, 2004). These

genotypes were evaluated for growth and productiv-

ity traits under a range of salinity and alkalinity stress

treatments, as well as for ionic (Na? and K?)

accumulation and their compartmentalization in dif-

ferent plant parts. QTL-NILs were preferred for this

study because they offer a unique opportunity to

focus the analysis on the effects of a specific genomic

region containing the QTL in an otherwise uniform

genetic background (Giuliani et al. 2005). These

genotypes were evaluated as test-cross hybrids by

crossing individual QTL-NILs to a common male

sterile line tester (843-A) rather than inbred lines per

se, to restore heterotic vigor in parental and QTL-

NILs inbred lines that otherwise were too weak for

effective screening under salt stress conditions

(Yadav et al. 2002).

The differential behavior in growth and produc-

tivity parameters of hybrids of the drought-tolerant

parent, drought-sensitive parent, and QTL-NILs was

evident right from the germination and seedling

emergence stage through to maturity under both

salinity and alkalinity treatments. Differences in

seedling emergence in parental genotypes and in

QTL-NILs were insignificant until the salinity levels

reached 22 dS m-1. The differences were, however,

much more conspicuous at the salinity level of

26 dS m-1. In the drought-sensitive parent an 80%

reduction in seedling emergence was recorded at this

salinity level compared to 50% in the drought-

tolerant parent PRLT 2/89-33, and about 41% on

average in QTL-NILs (Fig. 1A). A similar trend was

observed for growth parameters at the vegetative

stage (24 DAS), where greater shoot growth was

recorded in the drought-tolerant parent and the QTL-

NILs than the drought-sensitive parent under both

salinity and alkalinity conditions. Similarly, at matu-

rity, under the highest salinity level (ECiw

12 dS m-1), stover yield and total biomass yield

were reduced by 26 and 16%, respectively, in the

drought-tolerant parent PRLT 2/89-33 compared

to 43 and 44% in the drought-sensitive parent H 77/

833-2.

Ionic accumulation and compartmentalization in

different plant parts at both seedling (Fig. 1B) and

maturity stages (Figs. 2, 3, 4) correlated with growth

and yield parameters in parents and QTL-NILs. The

drought-sensitive parent H 77/833-2 accumulated

significantly higher concentrations of toxic Na? in

shoot parts, irrespective of the growth stage, than the

drought-tolerant parent under both salt stress treat-

ments. It is worth noting that the difference in Na?

accumulation was evident only in leaves and not in

the rest of the shoot parts (i.e. nodes, internodes) of

the parental genotypes and QTL-NILs (Figs. 2, 3).

For example, at the highest salinity level (ECiw

12 dS m-1), the drought-sensitive parent accumu-

lated more than twice the concentration of Na? in

leaves compared to the drought-tolerant parent. As

for growth parameters, the QTL-NILs showed a

pattern of salt accumulation largely similar to that of

the drought-tolerant parent (PRLT 2/89-33) from

which this DT-QTL was introgressed. A lower

accumulation of Na? in leaves is a well-known

phenomenon associated with salt tolerance in pearl

millet (Krishnamurthy et al. 2007; Sharma and Gill

1992). The relationship between salt tolerance and

Na? concentration in leaves is also a well-known

mechanism reported in many plant species and has

shown promise as a selection tool for salinity

tolerance (Akita and Cabusaly 1990; Ashraf and

Khanum 1997; Ashraf and O’Leary 1996; Chippa and

Lal 1995; Lauchli 1984; Munns and James 2003;

Poustini and Siosemardeh 2004; Yeo and Flowers

1984; Yeo 1992; Zhu et al. 2004). In durum wheat,

for instance, genotypes with lower Na? concentration

in leaves yielded higher shoot biomass yield after

growing for 4 weeks in saline culture solution

(Munns and James 2003), and higher grain yield

after growing for 4 months in saline soil (Hussain

et al. 2003).

The other finding of the present study was that

Na? accumulation from root to shoot increased at a

higher rate in the drought-susceptible parent H 77/

833-2 (68.6%) compared to the drought-tolerant

parent PRLT 2/89-33 and the QTL-NILs (which on

average showed an increase by 37.3%) at the higher

salinity treatment. The well-documented differences

in salt tolerance between durum and bread wheat is

reported to be related to low rates of Na? transport

into shoot parts from roots (Gorhom et al. 1990;

Hussain et al. 2004; Munns et al. 2003). Interestingly,

we also found that Na? transport was independent of

K? transport in our study, as the hybrids of the two

parental genotypes had similar K? concentration in

their shoot in control as well as in the highest salinity

220 Mol Breeding (2011) 27:207–222

123

and alkalinity treatments. Furthermore, the pattern

and the concentration of K? in QTL-NILs was

dissimilar to that of either parent, suggesting that this

DT-QTL does not affect K? transport. Similar results

(that Na? accumulation is independent of K? accu-

mulation) have been reported in other plant species

(Flowers and Yeo 1981; Hussain et al. 2004; Munns

2002) including pearl millet (Krishnamurthy et al.

2007). From these data it can be concluded unam-

biguously that lower transport of Na? from roots to

shoots, together with preferential compartmentaliza-

tion of Na? in nodes and internodes leading to lower

Na? accumulation in leaves, is the mechanism

operating under salt stress, associated with this

drought tolerance QTL. This mechanism is in agree-

ment to what is known in pearl millet and other

species but different to what is reported in sorghum

where salt tolerance was largely dependent on

the capacity of roots to retain Na? (Netondo et al.

2004).

It is also worth highlighting that although the

performance of most of the QTL-NILs hybrids

analyzed in this study was largely similar to the

donor parent under salt stresses, not all QTL-NILs

behaved similarly. For example, ICMR 01046 and

ICMR 02042 recorded higher reductions in seed-

ling emergence (on the pattern of drought-sensitive

parent H 77/833-2) in the Petri plate experiment.

Similarly, higher reductions in biomass and shoot

weight under higher alkalinity stress (pH 9.4) were

recorded for ICMR 01046 and ICMR 02044. Also,

plant head weight showed maximal reductions in

ICMR 01031 and 01040, and ICMR 01046 and

02044, under highest salinity (ECiw 12 dS m-1)

and alkalinity (pH 9.4) treatments, respectively.

This differential response among QTL-NILs

hybrids could be due to the variable size of the

donor segment around the DT QTL on LG 2 that

has been introgressed into the QTL-NILs evaluated

in the study. Serraj et al. (2005) also reported

previously that all QTL-NILs did not behave

uniformly under terminal drought stress conditions.

ICMR 01029 and 01031 were found to be superior

in their study for yield maintenance while ICMR

02042 had a yield response more like H 77/833-2

and ICMR 02044 had an intermediate yield

response under terminal drought stress conditions.

The differential response of QTL-NILs emphasizes

the need for fine mapping of this important QTL

interval on LG 2. Efforts in this direction are

currently underway in our laboratory, in which a

high-resolution cross segregating only for the DT

QTL interval on LG 2 has been advanced using

QTL-NIL ICMR 01029 and H 77/833-2 as parental

genotypes. This highly specialized cross will not

only generate new markers within the QTL interval

and delimit the QTL region but also will serve as a

useful material to test association of putative

physiological processes associated with this impor-

tant QTL.

Conclusion

The results of the present study clearly establish that

the DT-QTL region on LG 2 contributed by PRLT 2/

89-33 also exerts favorable effects on growth and

productivity parameters of pearl millet under saline

and alkaline conditions. This DT-QTL does so by

limiting Na? transport to the photosynthesising

leaves. The exact mechanism by which the DT-

QTL limits Na? accumulation in leaves, however,

could not be established from the data generated in

this study. Preliminary physiological studies avail-

able on the drought-tolerant QTL donor parent and on

the QTL-NILs (Kholova et al. 2008) indicate that

they have lower transpiration rates and higher ABA

concentrations relative to the drought-sensitive recur-

rent parent H 77/833-2. Both low transpiration rate

(Munns and Richards 2007; Yadav et al. 1996) and

high ABA concentration (Voisin et al. 2006) can play

an important role in both Na? uptake and drought

tolerance and their possible roles in determining low

Na? transport observed in the QTL donor parent and

QTL introgressed NILs will be investigated and

reported in due course.

Acknowledgments The work reported in this study was

conducted under the auspices of the Collaborative Project with

Scientists & Technologists of Indian Origin Abroad Program

(CP-STIO) award to P.C.S. and R.S.Y. by the Department of

Science and Technology (DST), Government of India.

Financial support provided by the DST via grant number

DST/INT/CP-STIO/2006-07/60/2006 is gratefully acknow-

ledged. Plant materials used in the study was generated in a

separate project funded by the Biotechnology and Biological

Sciences Research Council (BBSRC) and Department for

International Development (DFID) to R.S.Y. via grant number

BB/F004133/1. The authors are grateful to Professor Tim

Flowers for critically reviewing the manuscript.

Mol Breeding (2011) 27:207–222 221

123

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