Identification of quantitative trait loci associated with powdery mildew resistance in mungbean using ISSR and ISSR-RGA markers

To identify the powdery mildew (PM) resistance gene in mungbean, inter-simple sequence repeat (ISSR) markers and newly developed ISSR-anchored resistance gene analog (ISSR-RGA) markers were evaluated. When F_2:7 and F_2:8 recombinant inbred line populations derived from a cross between CN72 (susceptible cultivar in Thailand) and V4718 (resistant line from Asian Vegetable Research and Development Center) were evaluated for PM resistance under field conditions, the PM resistance gene from V4718 was found to be inherited as a single major gene. Fifteen out of 75 ISSR primers produced 27 DNA bands putatively associated with PM resistance in bulk segregant analysis (BSA). Ten ISSR primers were combined with four RGA primers homologous to the nucleotide-binding site and kinase domains of resistance (R) genes to generate 40 ISSR-RGA primer combinations. When these 40 ISSR-RGA primer combinations and 10 corresponding ISSR primers were used in BSA, 873 ISSR and 756 ISSR-RGA loci were amplified. Fifty-two of 756 ISSR-RGA loci were new, and 11 of these 23 ISSR-RGA loci were putatively associated with the PM resistance. Simple linear regression confirmed that 5 of the 27 ISSR markers and 3 of the 11 ISSR-RGA markers were significantly associated with the PM resistance gene. When these eight ISSR and ISSR-RGA markers were used for quantitative trait loci (QTL) analysis, multiple interval mapping identified a major QTL, qPMC72V18-1, explaining up to 92.4% of the phenotypic variation, flanked by I42PL229 and I85420 markers at the distance of 4 and 9 cM, respectively. These results suggest that ISSR and ISSR-RGA markers are highly efficient tools for mapping PM resistance gene in mungbean. The markers closely linked to the PM resistance gene will be useful for future marker-assisted selection to develop mungbean varieties resistant to PM.