Development and validation of diagnostic KASP markers for MYMIV resistance in urdbean

Mungbean Yellow Mosaic India Virus (MYMIV) is a major constraint to productivity in urdbean, necessitating the development of reliable molecular markers for resistance breeding. The present study reports the development of two Kompetitive Allele Specific PCR (KASP) markers for the Tobacco Mosaic Virus (TMV) resistance gene and the F-box/LRR resistance gene. These markers enable reliable discrimination between resistant and susceptible genotypes in urdbean. The highly MYMIV-resistant genotypes identified in this study possessed resistance alleles for both genes, whereas other resistant genotypes carried the resistance allele for either one of the two genes. This finding broadens the scope of marker-assisted pyramiding of these resistance alleles to enhance the genetic resistance of susceptible or moderately resistant genotypes. Among the urdbean genotypes, most resistant genotypes harboured the resistance allele (GG) for the TMV gene. However, only two highly resistant genotypes (IPU11-02 and PU-31) possessed resistance allele for both the TMV (GG) and F-box/LRR (TT) genes. In mungbean, the susceptible allele (AA) of the F-box/LRR gene was observed in 12 genotypes, while the remaining 12 genotypes exhibited a null allele, indicating the absence of amplification. This allelic distribution, along with the TMV gene status, largely explains the comparatively lower degree of genetic resistance to MYMIV in mungbean relative to urdbean. The developed KASP markers were further validated across six additional Vigna species. Most genotypes from these Vigna species carried the susceptible allele for the TMV gene, except PRR 2007-2 of Vigna umbellata, which exhibited a high level of resistance to MYMIV under field conditions. For the F-box/LRR gene, no alleleic amplification was observed in most genotypes from six Vigna species, suggesting the presence of divergent or novel alleles; however, PRR 2007-2 showed amplification with the susceptible allele (AA). In conclusion, the KASP markers developed for the TMV and F-box/LRR genes provide an efficient and robust tool for marker-assisted introgression of MYMIV resistance alleles. Notably, these markers are effective and applicable in urdbean. These markers can be readily used in breeding programs, including inter-specific crosses involving diverse Vigna species, to accelerate the development of MYMIV-resistant cultivars/germplasm.