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

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 F-2 (KPS1 x V4718) and BC1F1 [(KPS1 x V4718) x KPS1] populations developed from crosses between the CLS-resistant mungbean V4718 and CLS-susceptible cultivar Kamphaeng Saen 1 (KPS1). CLS resistance in F-2 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. Subsequently, 69 polymorphic markers were analyzed in the F-2 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 F-2 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.