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

La relation entre le gene de resistance aux aphids,
Rac, avec de nombreux loci polymorphiques qui
controlent les traits morphologiques et l'isozyme asparate
d'amino transferase (AAT) etait etudie chez le niebe dans
l'optique d'identifier les marqueurs facilement heritables et
facilement identifiables pour la resistance aux aphides et
envue de faire la distinction entre Rac1 et Rac2
tels que precaunise par Pathak (1988). Les populations F2 et
F2 - derivees de F3 des croisements IT87S-1459 x Tvu 946
segregues pour Rac2 ont ete cotees pour leurs
differents traits morphologiques polymorphiques. Le locus pd,
controllant la couleur de pedoncule etait associe au
Rac1 et Rac2 (P<=0.05). Les frequences de
recombination estimees par une methode de probabilite maximale
etaient de 26 +/- 8.3% et de 35 +/- 7.5% pour la
co-segregation des Rac1-pd et
Rac-2-pd-respectivement; ce qui indique que la
Rac2 n'etait pas differents l'une de l'autre. Aucune
relation n'a ete revelee entre les genes de resistance aux
aphides et les genes qui controllent les autres traits
morphologiques polymorphiques ou l'isozyme AAT.

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.