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.