A GENETIC-LINKAGE MAP OF COWPEA (VIGNA-UNGUICULATA) DEVELOPED FROM A CROSS BETWEEN 2 INBRED, DOMESTICATED LINES

We have constructed a genetic linkage map within the cultivated gene p ool of cowpea (2n = 2x = 22) from an F-8 recombinant inbred population (94 individuals) derived from a cross between the inbreds IT84S-2049 and 524B. These breeding lines, developed in Nigeria and California, s how contrasting reactions against several pests and diseases and diffe r in several morphological traits. Parental lines were screened with 3 32 random RAPD decamers, 74 RFLP probes (bean, cowpea and mung bean ge nomic DNA clones), and 17 AFLP primer combinations. RAPD primers were twice as efficient as AFLP primers and RFLP probes in detecting polymo rphisms in this cross. The map consists of 181 loci, comprising 133 RA PDs, 19 RFLPs, 25 AFLPs, three morphological/classical markers, and a biochemical marker (dehydrin). These markers identified 12 linkage gro ups spanning 972 cM with an average distance of 6.4 cM between markers . Linkage groups ranged from 3 to 257 cM in length and included from 2 to 41 markers, respectively. A gene for earliness was mapped on linka ge group 2. Seed weight showed a significant association with a RAPD m arker on linkage group 5. This map should facilitate the identificatio n of markers that ''tag'' genes for pest and disease resistance and ot her traits in the cultivated gene pool of cowpea.