INDEPENDENT INHERITANCE OF STRIGA AND ALECTRA RESISTANCE IN COWPEA GENOTYPE B301

Cowpea [Vigna unguiculata (L.) Walp] is a major food legume in the sem i-arid region of Sub-Saharan Africa. Recently, two parasitic weeds, St riga [Striga gesnerioides (Willd.) Vatke] and alectra [Alectra vogelii Benth.] have become a major threat to cowpea cultivation in this regi on. A landrace of cowpea from Botswana, B301, is resistant to both par asites and genetic studies have revealed a single dominant gene for st riga resistance and duplicate dominant genes for alectra resistance. T his study was undertaken to ascertain whether the genes controlling re sistance to these parasitic weeds are independent of each other. Genot ype B301 was crossed to a susceptible variety, IT84S-2246-4, and F1, F 2, and backcross plants were screened for joint infection by pot cultu re technique. Roots of each plant were washed free of soil 10 wk after planting and examined for the attachment of striga and alectra. All p lants of B301, and F1 and backcross plants involving 8301, were comple tely free of striga and alectra attachments, whereas all plants of IT8 4S-2246-4 were infected by both parasites. The F2 generation segregate d into 349 resistant to both, 118 susceptible to striga and resistant to alectra, 15 susceptible to alectra and resistant to striga, and 8 s usceptible to both striga and alectra, which fit a trigenic segregatio n ratio of 45: 15:3:1. Backcross F1 plants involving IT84S-2246-4 segr egated in a ratio of 3:3:1:1. The data indicated that genes conferring resistance to striga and alectra in B301 are non-allelic and independ ent of each other.