AFLP markers linked to resistance against Striga gesnerioides race 1 in cowpea (Vigna unguiculata)

Amplified fragment length polymorphism (AFLP) analysis was used in combination with bulked segregant analysis (BSA) to identify molecular markers linked to two cowpea (Vigna unguiculata (L.) Walp.) genes conferring resistance to Striga gesnerioides race 1. After AFLP analysis of an F-2 population derived from a cross between the resistant cultivar Gorom and the susceptible cultivar Tvx 3236, seven AFLP markers were identified that are linked to Rsg3, the gene conferring race I resistance in 'Gorom'. The distances between these markers and Rsg3 ranged from 9.9 to 2.5 cM, with two markers, E-AGA/M-CTA(460) and E-AGA/M-CAG(300), flanking Rsg3 at 2.5 and 2.6 cM, respectively. Analysis of a second F-2 population derived from the cross between 'Tvx 3236' and the resistant cultivar IT81D-994 identified five AFLP markers linked to the race I resistance gene 994-Rsg present in 'IT81D-994'. The two markers showing the tightest linkage to the 994-Rsg locus were E-AAG/M-AAC(450) and E-AAG/M-AAC(150) at 2.1 and 2.0 cM, respectively. Two of the markers linked to 994-Rsg, E-AGA/M-CAG(300) and E-AGA/M-CAG(450), were also linked to Rsg3. The identification of molecular markers in common between the two sources of race 1 resistance suggests that either Striga resistance genes are clustered in these plants or that these loci are allelic. Mapping of the resistance loci within the cowpea genome revealed that three markers linked to Rsg3 and (or) 994-Rsg are located on linkage group 6.