Quantitative trait loci mapping of Cercospora leaf spotresistance in mungbean, Vigna radiata (L.) Wilczek

Sompong Chankaew • Prakit Somta •

Worawit Sorajjapinun • Peerasak Srinives

Received: 15 March 2010 / Accepted: 23 June 2010 / Published online: 14 July 2010

� Springer Science+Business Media B.V. 2010

Abstract Cercospora leaf spot (CLS) caused by the

fungus Cercospora canescens Illis & Martin is a

serious disease in mungbean (Vigna radiata (L.)

Wilczek), and disease can reduce seed yield by up to

50%. We report here for the first time quantitative trait

loci (QTL) mapping for CLS resistance in mungbean.

The QTL analysis was conducted using F2 (KPS1 9

V4718) and BC1F1 [(KPS1 9 V4718) 9 KPS1]

populations developed from crosses between the

CLS-resistant mungbean V4718 and CLS-susceptible

cultivar Kamphaeng Saen 1 (KPS1). CLS resistance in

F2 populations was evaluated under field conditions

during the wet seasons of 2008 and 2009, and

resistance in BC1F1 was evaluated under field

conditions during the wet season in 2008. Seven

hundred and fifty-three simple sequence repeat (SSR)

markers from various legumes were used to assess

polymorphism between KPS1 and V4718. Subse-

quently, 69 polymorphic markers were analyzed in the

F2 and BC1F1 populations. The results of segregation

analysis indicated that resistance to CLS is controlled by

a single dominant gene, while composite interval

mapping consistently identified one major QTL (qCLS)

for CLS resistance on linkage group 3 in both F2 and

BC1F1 populations. qCLS was located between markers

CEDG117 and VR393, and accounted for 65.5–80.53%

of the disease score variation depending on seasons and

populations. An allele from V4718 increased the

resistance. The SSR markers flanking qCLS will

facilitate transferral of the CLS resistance allele from

V4718 into elite mungbean cultivars.

Keywords Mungbean � Cercospora leaf spot �Simple sequence repeat � Vigna radiata �QTL � Cercospora canescens

Introduction

Mungbean, Vigna radiata (L.) Wilczek, is an impor-

tant legume crop in South and Southeast Asia. Over

90% of mungbean production occurs in South Asia,

where India is the largest producer. In some countries

such as Thailand and the Philippines mungbean is the

Electronic supplementary material The online version ofthis article (doi:10.1007/s11032-010-9478-1) containssupplementary material, which is available to authorized users.

S. Chankaew

Program in Plant Breeding, Faculty of Agriculture

at Kamphaeng Saen, Kasetsart University,

Kamphaeng Saen, Nakhon Pathom 73140, Thailand

P. Somta � P. Srinives (&)

Department of Agronomy, Faculty of Agriculture

at Kamphaeng Saen, Kasetsart University,

Kamphaeng Saen, Nakhon Pathom 73140, Thailand

e-mail: agrpss@yahoo.com

W. Sorajjapinun

AVRDC-The World Vegetable Center, Asian Regional

Center, Kasetsart University, Kamphaeng Saen,

Nakhon Pathom 73140, Thailand

123

Mol Breeding (2011) 28:255–264

DOI 10.1007/s11032-010-9478-1

most important legume crop, popular because of its

early maturity (60–65 days), relative drought toler-

ance and ability to fix atmospheric nitrogen in

association with soil Rhizobium. Seeds of mungbean

contain high levels of protein (ca. 25%) with high-

quality amino acid profiles, and thus become an

inexpensive source of dietary protein for poor people

and vegetarians in the region. Sprouts and green pods

of mungbean are considered high in vitamins and

minerals. Plant parts are used as fodder and manure.

Although mungbean can be grown as a monocrop, it

is commonly grown as a component in various

cropping systems owing to its early maturity.

One of the most important factors affecting

mungbean production in Asia is Cercospora leaf spot

(CLS) disease, a foliar disease caused by the

biotrophic fungus Cercospora canescens Illis &

Martin (Chupp 1953). The disease is widespread in

Asia and especially devastating in the warm-wet

growing season. The fungus initially causes spotting

on mungbean leaves; the spots increase in number

and size during flowering, but the increment is most

rapid at the pod-filling stage. In susceptible varieties,

infection expands rapidly resulting in premature

defoliation and reduction in size of pods and seeds

(Grewal et al. 1980), and thus causes yield losses of

up to 50% if there is no protection (AVRDC 1984).

Although this disease can be controlled by spraying

with fungicide, the practice increases farmers’ pro-

duction costs and has adverse affects on human health

and the environment. Moreover, regular spraying can

cause development of chemical resistance in the

pathogen. The use of resistant varieties is the most

desirable strategy to manage the disease in an

economical and environmentally-friendly way.

Information on inheritance of resistance to CLS

disease is useful in breeding for resistant cultivars.

Genetic studies of inheritance of CLS resistance,

using different resistant sources, revealed that the

resistance is controlled by either a single dominant

gene (AVRDC 1974; Thakur et al. 1977; Lee 1980),

or a single recessive gene (Mishra et al. 1988), or

quantitative genes (AVRDC 1980; Leabwon and

Oupadissakoon 1984). Although the above informa-

tion is useful for breeders in developing the resistant

varieties, progress in selecting CLS-resistant geno-

types in large breeding programs is still limited. This

is mainly due to the fact that CLS occurs only in the

rainy season, which is the primary growing season for

mungbean. Thus field evaluation for resistance can be

done in only one season per year, albeit mungbean is

considered among the shortest season crop in the

world and can be grown 3–4 times a year. Molecular

markers linking to the gene controlling resistance can

aid selection and advance the generation year-round

(Collard and Mackill 2008), thus overcoming the

limitations of conventional breeding methods. Gene

or quantitative trait loci (QTL) mapping in mungbean

has been conducted for resistance to insects and dis-

eases such as bruchids, powdery mildew and mung-

bean yellow mosaic virus (see Somta and Srinives

2007 for review), but not CLS.

In this paper, we report for the first time QTL

mapping for resistance to Cercospora leaf spot in

mungbean. The objectives of this study were to

determine the genetics and genome position of CLS

resistance in mungbean accession V4718.

Materials and methods

Plant materials and DNA extraction

F1, F2 and BC1F1 mungbean populations were

developed from V4718 and Kamphaeng Saen 1

(KPS1). V4718 is an accession originally from India

and is reported to be highly resistant to CLS in

Taiwan (AVRDC 1980). It also showed high resis-

tance to the disease in Thailand (Somta P, unpub-

lished data). KPS1 is a commercial mungbean

cultivar from Thailand susceptible to CLS. V4718

was used as male parent and crossed onto KPS1 to

developed F1 hybrids. The F1 hybrids were self-

pollinated and used as female parent to backcross

to KPS1 in order to develop F2 and BC1F1 popula-

tions, respectively. F2 and BC1F1 individuals were

self-pollinated, and their F3 and BC1F2 seeds were

used for phenotyping. The F2 and BC1F1 mapping

populations comprised 155 and 76 individuals,

respectively.

Total genomic DNA was extracted from young

leaves of KPS1, V4718, F2 and BC1F1 individuals

using the method described by Lodhi et al. (1994)

with a slight modification. The DNA was quantified

against a lambda DNA on 1.0% agarose gel stained

with ethidium bromide and diluted to 1 ng/ll for PCR

amplification.

256 Mol Breeding (2011) 28:255–264

123

Evaluation of disease resistance

For the F2 population, the parents, F1 and F2:3

progenies were planted in a randomized complete

block design (RCBD) with two replications in the wet

seasons (August to October) of 2008 and 2009 at

Kasetsart University, Kamphaeng Saen Campus,

Nakhon Pathom, Thailand. In the case of the BC1F1

population, the parents, F1 and BC1F2 progenies were

planted in RCBD with two replications during the wet

season of 2008. In all experiments, each entry was

sown in a single row of 2 m long with 12.5 cm intra-

row and 50 cm inter-row spacings, with two plants

per hill (ca. 32 plants/row). Ten days prior to planting

these materials, a highly susceptible mungbean

germplasm, V1197, was sown around and between

the experimental blocks as a natural source of CLS

inoculums. At 20, 25 and 30 days after planting

(DAP), spore suspensions were artificially inoculated

to all entries. After inoculation, conidia taken from

infected plants were examined using a light micro-

scope to confirm that the disease symptoms were the

results of infection by C. canescens. Infection on the

leaves of each plant was scored for CLS reaction at

40 DAP on a scale of 1–5, where 1 = no visual

disease infection, 2 = 1–25% leaf area infected,

3 = 26–50% leaf area infected, 4 = 51–75% leaf

area infected, and 5 = 76–100% leaf area infected.

Scoring was conducted by a panel of three trained

staff. Lines with the disease score 1 or 2 were

classified as resistant, and those with disease score 3,

4 or 5 were considered susceptible. The average

scores across plants in each row were used for

statistical and QTL analyses in each of the three

experiments.

SSR marker analysis

Seven hundred and fifty-three simple sequence repeat

(SSR) primer pairs from various legumes were used

to detect polymorphism between KPS1 and V4718.

Among them, 433 were from mungbean [V. radiata

(L.) Wilczek] (Kumar et al. 2002a, b; Gwag et al.

2006; Somta et al. 2008, 2009; Seehalak et al. 2009;

Tangphatsornruang et al. 2009), 188 from azuki bean

[V. angularis (Ohwi) Ohwi & Ohashi] (Wang et al.

2004), 46 from cowpea [V. unguiculata (L.) Walp.]

(Li et al. 2001), and 86 from common bean (Phase-

olus vulgaris L.) (Gaitan-Solıs et al. 2002; Guerra-

Sanz 2004; Buso et al. 2006; Blair et al. 2003). All

the polymorphic markers were used to analyze the F2

population. Upon linkage map construction in the F2

population, only polymorphic markers on linkage

group 3 were used to analyze the BC1F1 population.

PCR was carried out in a total volume of 10 ll

containing 2 ng of DNA template, 19 Taq buffer,

2 mM MgCl2, 0.2 mM dNTPs, 1 U Taq DNA

polymerase (Fermentas) and 5 pmol each of forward

and reverse primers. Amplification was performed in

a GeneAmp� PCR System 9700 thermocycler

(Applied Biosystems) programmed as follow: 94�C

for 2 min followed by 35 cycles of 94�C for 30 s,

50–65�C for 30 s, 72�C for 1 min, with a final

extension step of 72�C for 10 min. The PCR products

were separated on 5% denaturing polyacrylamide gel

and visualized by silver staining.

Chi-square analysis

A chi-square (v2) test (Mather 1951) was used to

determine goodness of fit to 3:1 and 1:1 (resis-

tance:susceptible) ratio in the F2 and BC1F1 popula-

tions, respectively.

Linkage and QTL analyses

Genetic linkage maps were constructed with JoinMap

3.0 (Van Ooijen and Voorrips 2001) using data from

the F2 population. The calculation was set with the

minimum logarithm of the odds (LOD score) at 3.0

and the maximum recombination frequency (r) at 0.5,

using the Kosambi mapping function (Kosambi

1944). Since genetic linkage maps of Asian Vigna,

which mungbean belongs to, are highly conserved

(Chaitieng et al. 2006; Somta et al. 2006), markers

that were common to the azuki bean map reported by

Han et al. (2005) were compared and assigned to

linkage groups. In BC1F1 population, only linkage

group 3 was constructed, and used for QTL

confirmation.

QTL associating with CLS resistance were pre-

liminarily determined by single regression analysis

(Kearsey and Pooni 1996) using R-program. Single

marker analysis is useful for identifying marker(s)

linked to a trait or a QTL. It also gives a clue to the

number, effect and location of the QTL for a trait. To

locate QTL for resistance to CLS, a composite

interval mapping (CIM) (Zeng 1994) was performed

Mol Breeding (2011) 28:255–264 257

123

using WinQTL Cartographer 2.5 (Wang et al. 2007).

The analysis was done on the data of line means from

individual experiments. Permutation tests (Churchill

and Doerge 1994) were run 10,000 times at the

significance level of P = 0.01 to determine a LOD

score threshold for declaring a significant QTL.

Results

Mode of inheritance of CLS resistance

In the experiments conducted in 2008, disease

symptoms of CLS appeared at 20 days after inocu-

lation (DAI). KPS1 was highly susceptible (disease

score 5) to the disease, whereas V4718 was immune

to the disease (disease score 1). All F1 plants were

immune to the disease, suggesting that CLS resis-

tance in V4718 was conditioned by a dominant

gene. F2 and BC1F1 progenies differed in their CLS

response. The disease scores varied from 1 to 5 in

both populations with means of 2.26 and 3.60,

respectively (Fig. 1). In the F2 population, 116 lines

were classified as resistant and 39 lines as suscepti-

ble. Chi-square analysis revealed that the segregation

fitted with a 3:1 resistant:susceptible ratio (v2 =

0.002, P = 0.963) (Table 1). In the BC1F1 popula-

tion, 30 and 46 lines were classified as resistant and

susceptible, respectively. The segregation followed

a 1:1 resistant:susceptible ratio (v2 = 3.368, P =

0.067) (Table 1). These results indicated that resis-

tance to CLS disease in V4718 was inherited to KPS1

as a single dominant gene.

The result from the F2 population conducted in

2009 was similar to that of 2008. The disease

symptoms first appeared at 20 DAI. KPS1 was highly

susceptible, while V4718 and the F1 population were

highly resistant. Disease scoring in the F2 plants

ranged from 1 to 4.50 with the mean of 1.97 (Fig. 1),

and again 116 of them (although not exactly the same

lines) were classified as resistant and 39 as suscep-

tible (Table 1). The results confirmed that CLS

resistance in V4718 was conditioned by a single

gene.

Construction of an SSR linkage map

The genomes of V4718 and KPS1 were rather

similar. Although 496 out of 753 (65.87%) SSR

markers amplified DNA of the two genotypes

(Table 2), only 69 (13.91%) of the amplifiable

markers showed polymorphism. Of these SSRs, 27

were from mungbean, 41 from azuki bean, and 1

from cowpea (Table 2). None of the common bean

SSRs showed polymorphism between the parents. In

the F2 population, 56 markers could be assigned to

the linkage map (Fig. 2), while 13 markers remained

unlinked. The linkage map consisted of 11 linkage

groups (LGs) (LOD C 3) with a total genetic distance

(a)

(b)

(c)

Fig. 1 Frequency distribution of disease scores for response to

Cercospora leaf spot in the F2 population (KPS1 9 V4718)

evaluated in rainy season of 2008 (a) and 2009 (b), and in

BC1F1 population [(KPS1 9 V4718) 9 KPS1] evaluated in

rainy season of 2008 (c)

258 Mol Breeding (2011) 28:255–264

123

of 995.6 cM (Fig. 2) and an average density of 17.78

cM per marker. The LGs were named after azuki

bean LGs reported previously by Han et al. (2005).

Based on 30 common markers locating on our linkage

map and that of Han et al. (2005), all of them were

conserved on both maps with a few inversions of

marker order (Electronic Supplementary Material

S1). This indicates high genome homology between

mungbean and azuki bean.

When all the markers on LG 3 of the F2 linkage

map were used to construct a linkage map in the

BC1F1 population, LG 3 of the BC1F1 was 59.2 cM in

length.

Locating the QTL conditioning CLS resistance

Single regression analysis in the F2 population using

phenotypic data from the years 2008 and 2009 showed

that seven markers, namely CEDC031, CEDG044,

CEDG084, CEDG117, CEDG305, VR108 and

VR393, associated with CLS resistance (P \ 0.01)

(Table 3). All of them were located on LG 3, except

CEDG044 which was located on LG 11 (Fig. 2).

When the 2008 data were employed, the coefficient of

determination (R2) of these markers ranged from

3.26% (CEDG044) to 50.71% (VR108). From the

2009 data, the R2 of the seven markers ranged from

2.48% (CEDG044) to 44.55% (CEDG117). All the

markers were also found associating with CLS resis-

tance in the BC1F1 population (Table 3). The R2 of the

markers ranged from 6.11% (CEDG044) to 80.81%

(CEDG117).

Permutation analyses (10,000 runs at P = 0.01)

for the 2008 and 2009 data of the F2 population

revealed that LOD score thresholds for QTL were

19.4 and 15.8, respectively. In both years, CIM

consistently identified one major QTL for CLS

resistance (Table 4; Fig. 3). The QTL was designated

qCLS-1. It was located between markers CEDG117

and VR393 on LG 3 at 26.91 and 24.91 cM using the

2008 and 2009 data, respectively. The qCLS-1

showed a LOD score of 42.91 and 29.13, and

explained 78.22 and 65.15% of the phenotypic

variation in the 2008 and 2009 data, respectively.

Additive effects of the qCLS-1 were –1.46 and –0.81

while dominant effects were –0.76 and –0.50, in the

disease scores for 2008 and 2009 data, respectively.

The allele from V4718 contributed to the reduction in

disease score (increasing resistance).

The QTL for resistance identified in the F2

population was confirmed by the analysis in BC1F1

population. The LOD score threshold for QTL in the

BC1F1 population as determined by permutation was

16.7. CIM detected one major QTL, designated

qCLS-2, on LG 3 at 31.6 cM between markers

CEDG117 and VR393 (Table 4; Fig. 3). qCLS-2 was

1.9 and 6.6 cM away from CEDG117 and VR393,

respectively. The QTL exhibited a LOD score of

32.15 and accounted for 80.53% of the disease

variation. The additive effect of the qCLS-2 was

–2.92 of disease score, while the dominance effect

could not be estimated in a backcross model. The

allele from V4718 decreased the disease score and

appeared to be the same as qCLS-1.

Table 1 Segregation in reaction to CLS in F2 and BC1F1 populations from the cross KPS1 9 V4718

Population Year tested No. of lines tested No. of resistant:susceptible lines v2 valuea Probability

F2 2008 155 116:39 0.002 0.963

2009 155 116:39 0.002 0.963

BC1F1 2008 76 30:46 3.368 0.067

a The v2 value was tested for goodness-of-fit against 3:1 ratio and 1:1 ratio for F2 and BC1F1, respectively

Table 2 The number of SSR markers from mungbean, azuki

bean, cowpea and common bean that were screened in KPS1

and V4718 showing different rates of amplification and

polymorphism

Sources of SSR Number of SSR markers

Screened Amplified (%) Polymorphic (%)

Mungbean 433 305 (70.43) 27 (8.85)

Azuki bean 188 129 (68.62) 41 (31.78)

Cowpea 46 22 (47.83) 1 (4.55)

Common bean 86 40 (46.51) 0 (0.0)

Total 753 496 (65.87) 69 (13.91)

Mol Breeding (2011) 28:255–264 259

123

Discussion

Although several mungbean accessions were identi-

fied as highly resistant to CLS disease, only a few of

them (including V4718) showed stable resistance in

different seasons and years in Taiwan (Hartman et al.

1993). We demonstrated in this study that V4718 also

exhibited a stable resistance to CLS in Thailand over

2 years. Therefore, V4718 is a potential source for

exploiting the resistance gene.

Broad- and narrow-sense heritability of CLS

resistance have been estimated to be as high as 99

and 75%, respectively (Hartman et al. 1993). How-

ever, different modes of inheritance of the resistance

were reported by different research groups (AVRDC

1974, 1980; Thakur et al. 1977; Mishra et al. 1988;

Lee 1980), suggesting that there may be more than

one source of resistance to CLS. In our study, the

segregation of 3:1 and 1:1 for resistant and suscep-

tible progenies in the F2 and BC1F1 populations,

respectively, confirmed that a single dominant gene

controls the resistance. Thus it should not be difficult

for a plant breeder to transfer the resistance gene

from V4718 to susceptible cultivars by using standard

VR4130.0

CEDG2847.4

CEDG00619.7

LG2A

CEDG2440.0

VR25623.3

GBssr-MB8745.6

DMB-SSR16066.4

CEDAAG00299.0

CEDC050107.1

LG2B

CEDC0310.0CEDG0846.4VR10811.3

CEDG11720.9

VR39333.7

CEDG30550.9

LG3

CEDC0550.0

DMB-SSR19944.9CEDG15448.3

CEDG08866.3

CEDG232108.9

DMB-SSR167134.1

VR-SSR035157.1

LG4

CEDG0140.0

MB-SSR3942.7

DMB-SSR21856.9

LG5

VR0950.0

CEDG03750.8

CEDG12171.5

CEDG245119.9

LG6

CEDG0730.0

CEDG04040.4GBssr-MB09145.5

CEDG24786.2

CEDG071138.2

LG8

VR-SSR0100.0

DMB-SSR13017.5

CEDG30429.5

CEDG25943.0

VM2779.0

MB-SSR8796.2VR098103.1

VR354120.0

CEDG228133.6

CEDG173152.0

LG9

VR2930.0

CEDG19829.5

LG10A

CEDG1160.0

CEDG15040.3

CEDG00850.1

CEDG02158.2

CEDG24379.6

LG10B

MB-SSR1640.0

VR30431.2VR30537.5

CEDG04444.7

CEDG18185.6

LG11

Fig. 2 An SSR linkage map of mungbean constructed from F2 population from the cross KPS1 9 V4718

260 Mol Breeding (2011) 28:255–264

123

breeding methods for a self-pollinated species such as

backcross, bulk and pedigree breeding.

We are the first group to identify QTL for CLS

resistance in mungbean. Identification of a single

major QTL for the resistance to CLS by CIM in both

F2 and BC1F1 is in agreement with the Mendelian

segregation of the resistance. The same QTL was

detected in different environments (years) and pop-

ulations, although the weather conditions between the

two environments were relatively different (Elec-

tronic Supplementary Material S2). Using the F2 data,

the QTL detected in 2008 and 2009 data were nearly

the same, while the variations explained by the QTL

(R2) were comparable. Therefore, the major QTL

detected is considered highly robust. Although

another small effect QTL was detected on LG 11

by marker regression analysis, its effect is too small

to use in marker-assisted selection (MAS) (Table 3).

The level of polymorphism between V4718 and

KPS1 is low, as only 13.91% of 496 SSR markers

were polymorphic. This is because the two mung-

beans were cultivated varieties. However, Xu et al.

(2008) reported that the gene pool of cultivated

mungbean is much narrower than that of azuki bean.

Table 3 SSR markers associated with Cercospora leaf spot disease in F2 and BC1F1 populations as revealed by single regression

analysis

Markers (LGa) Population Year 2008 Year 2009

R2 (%)b Probability R2 (%)b Probability

CEDG031 (3) F2 37.16 \0.0001 31.24 \0.0001

BC1F1 28.49 \0.0001

CEDG084 (3) F2 39.60 \0.0001 32.77 \0.0001

BC1F1 46.53 \0.0001

VR108 (3) F2 50.71 \0.0001 43.96 \0.0001

BC1F1 73.79 \0.0001

CEDG117 (3) F2 50.61 \0.0001 44.55 \0.0001

BC1F1 80.81 \0.0001

VR393 (3) F2 42.28 \0.0001 32.50 \0.0001

BC1F1 62.67 \0.0001

CEDG305 (3) F2 23.94 \0.0001 22.69 \0.0001

BC1F1 26.87 \0.0001

CEDG044 (11) F2 3.26 0.0151 2.48 0.0297

BC1F1 6.11 0.0205

a Linkage groupb Coefficient of determination

Table 4 Quantitative trait loci conditioning resistance to Cercospora leaf spot in the F2 (KPS1 9 V4718) and BC1F1

[(KPS1 9 V4718) 9 KPS1] populations as detected by composite interval mapping

Population Year QTL namea LGb Marker interval Position (cM)c LOD score PVE (%)d Additive

effect

Dominant

effect

F2 2008 qCLS-1 3 CEDG117–VR393 26.91 42.91 78.22 –1.46 –0.76

2009 qCLS-1 3 CEDG117–VR393 24.91 29.13 65.15 –0.81 –0.50

BC1F1 2008 qCLS-2 3 CEDG117–VR393 31.67 32.15 80.53 –2.92

a QTL that showed similar position and effect in the same population were assigned the same nameb Linkage groupc Position on the linkage groupd Percentage of phenotypic variance explained by the QTL

Mol Breeding (2011) 28:255–264 261

123

The low polymorphism between the parental mung-

beans resulted in low genome coverage of the genetic

linkage map developed in the current study. Although

the mungbean linkage map developed in this study

and the azuki bean linkage map developed by Han

et al. (2005) revealed high genome conservation,

our map is lacking in LG 1 and LG 7 (Electronic

Supplementary Material S1). Thus minor QTL in LG

1 and LG 7, if any exist, were not detected.

There are few reports of QTL studies in mungbean

(Somta and Srinives 2007). qCLS identified in this

study shows no linkage with QTL (genes) previously

reported in mungbean for resistance to insects [azuki

bean weevil (Callosobruchus chinensis L.) and pod-

sucking bug (Riptortus clavatus Thunberg)] (Hong

2006), and to powdery mildew disease (caused by

fungus Erysiphe polygoni D.C.) (Kasettranan et al.

2010). This confirms the report by Thakur et al.

Fig. 3 Position of the QTL conditioning Cercospora leaf spot

resistance (qCLS) and LOD score plotted for composite

interval mapping (CIM) on linkage group 3 in the F2 (a) and

BC1F1 (b) populations derived from the cross KPS1 9 V4718.

The solid and dashed lines parallel to the linkage map in

a represents LOD threshold from F2 data in 2008 and 2009,

respectively. The solid line parallel to the linkage map in

b represents LOD threshold from BC1F1 data in 2008

262 Mol Breeding (2011) 28:255–264

123

(1977) that genes conferring resistance to CLS and

powdery mildew disease inherited independently.

Thus it would be easier to apply MAS to select for

unlinked rather than linked genes in order to improve

resistance to these biotic stresses.

Since C. canescens cannot be maintained by

artificial culture and only occurs in the wet season,

traditional breeding for resistance can be done in only

one crop per year. However, field screening for

resistance is laborious and inefficient if the weather is

not suitable for disease occurrence or if the disease is

not uniformly distributed in the field. These limita-

tions and difficulties can be overcome by MAS. The

qCLS was confirmed for its position and effect, and

therefore CEDG117 and VR393 flanking it are

valuable tools for selecting CLS-resistant genotypes

in mungbean breeding programs by enabling the

breeder to select for resistance progenies off-season

and then confirm existence of the resistance gene by

evaluating the progenies in the wet season. This

should help accelerate breeding for CLS resistance in

mungbean.

Acknowledgments This research was supported by the

National Science and Technology Development Agency

(NSTDA), Thailand. S. Chankaew is grateful to NSTDA for a

Master student scholarship. The authors thank Dr. Akito Kaga of

the National Institute of Agrobiological Sciences, Japan, for

providing azuki bean SSR marker information on LG 3. We also

thank the Center for Agricultural Biotechnology, Kasetsart

University, Kamphaeng Saen Campus, Thailand for lab facilities.

References

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