Identification and Characterization of SSR Markers Linked to Yellow Mosaic Virus Resistance Gene(s) in Cowpea (Vigna unguiculata)

Abstract

Cowpea yellow mosaic virus (CYMV) infects all aerial parts of cowpea (Vigna unguiculata), causes loss of as much as 80-100 % crop yield (Chant, 1960; Gilmer et al., 1974; and Williams, 1977). The linkage of SSR markers to CYMV resistance was studied using 20 CYMV resistance lines and 20 susceptible lines of cowpea. Among 60 SSR primers used to screen polymorphism between stable resistance (GC-3) and susceptible (Chrodi) genotypes, only 4 primers were polymor- phic. These 4 SSR primer pairs were used to detect CYMV resistant genes among 40 cowpea genotypes. The polymorphism obtained was used to analyse the association of the linkage markers with CYMV resistant trait using QTXb20 software. In map maker analysis and QTL mapping application, four SSR markers (AG1/AF48383, VM31, VM1 and VM3) were mapped in the same chromosome covered 88.6cM calculated from 40 progenies with 53 crossovers. This segment of chromosome was located in a part of linkage group 2 of cowpea genetic map. A QTL for CYMV resistant trait was detected in association with three SSR loci (AG1/AF48383, VM31 and VM1) with absolute probability for the association. The interval QTL mapping showed 98.4 per cent of the resistance trait mapped in the region of three loci AGB1, VM31 & VM1 covered 32.1 cM, in which 95% confidence interval for the CYMV resistance QTL associated with VM31 locus was mapped within only 19 cM. This showed that QTL for CYMV resistant trait was highly heritable. The information provided by the identified markers would be very useful in breeding programs to select cowpea lines resistance to CYMV disease.