Construction of a genetic linkage map and QTL analysis using a recombinantinbred population derived from an intersubspecific cross of cowpea (Vigna unguiculata (L.) Walp.)

Cowpea (Vigna unguiculata (L.) Walp,) is an important grain legume crop com monly grown and consumed in many parts of the tropics and subtropics. A gen etic linkage map of cowpea was constructed using randomly amplified polymor phic DNA (RAPD) markers and a recombinant inbred (RI) population derived fr om the intersubspecific cross between IT84S-2246-4, an improved cowpea line , and TVNu 110-3A (Vigna unguiculata spp, dekindtiana var. pubescens), The map spanned 669.8 centiMorgans (cM) of the genome and comprised 80 mapped l oci (77 RAPD and 3 morphological loci) assembled into 12 linkage groups. Th e 12 linkage groups ranged in size from 14.0 to 175.4 cM, The distribution of interval sizes between adjacent markers on the cowpea map ranged from 0. 7 to 26.7 cM with an average distance of 9.9 cM, Random amplified polymorph ic DNA marker loci exhibiting distorted segregation ratios were detected. T he linkage map was used to locate quantitative trait loci (QTLs) for days t o flowering, days to maturity, pod length, seed/pod weight percent, leaf le ngth, leaf width, primary leaf length, primary leaf width, and the derived traits: leaf area and primary leaf area in the RI population, Significant ( p<0.01) quantitative trait locus (QTL) associations of marker loci were ide ntified for each trait. A total of 88 significant marker locus-trait associ ations were identified in all the linkage groups. Six markers with effects on these traits are yet unlinked. Both parental types contributed alleles w ith positive effects on these traits. The percentage of phenotypic variatio n associated with individual markers ranged from 6.6 to 16.9 %, Several reg ions of the genome affected more than one trait. The coincident map locatio ns of many QTLs for more than one trait corroborate the strong correlations observed between these traits.