Genetic linkage of the aphid resistance gene, Rac, in cowpea

Abstract

Linkage of the aphid resistance gene, Rac, with various polymorphic loci controlling morphological traits and aspartate amino-transferase isozyme (AAT) was studied in cowpea (Vigna unguiculata L. Walp) with the objective of identifying simply inherited and easily identifiable markers for aphid resistance and to distiguish between Rac1 and Rac2 reported by Pathak (1988). The F2 and F2 - derived F3 populations from crosses IT87S-1459 x Tvu 946 x ICV 5, and IT84S-2246 x Tvu 946 segragating for Rac1 and cross ICV 12 x Tvu 946 segragating for Rac2 were scored for various polymorphic morphological traits. Locus pd, controlling peduncle colour, was found to be linked to both Rac1 and Rac2 (P < 0.05). The recombination frequencies estimated by the maximum likehood method were 26 +/- 8.3% and 35 +/- 7.5% for Rac1-pd and Rac2-pd co-segregation, respectively, thus indicating that Rac1 and Rac2 were not different from one another. No linkage was found between aphid resistance genes and the genes controlling other polymorphic morphological traits or AAT isozyme.