COWPEA VIRUSES IN SENEGAL, WEST-AFRICA - IDENTIFICATION, DISTRIBUTION, SEED TRANSMISSION, AND SOURCES OF GENETIC-RESISTANCE

Viral diseases of cowpea (Vigna unguiculata subsp. unguiculata) in Sen egal were surveyed during the rainy seasons of 1990 and 1991. Sixty-si x symptomatic plant samples from five production areas were assayed fo r seven viruses by enzyme-linked immunosorbent assay (ELISA). Four rec ognized viruses, cowpea aphid-borne mosaic potyvirus (CABMV), cowpea m ottle carmovirus (CPMoV), cowpea severe mosaic comovirus (CSMV), and s outhern bean mosaic sobemovirus (SBMV), were detected in 34, 2, 1, and 1 samples, respectively. All are seed-transmissible in cowpea. Varian ts of an unknown potyvirus were also detected in 21 samples. These var iants occurred principally in new, improved CABMV-resistant cowpea gen otypes, and their combined incidence in plant samples was exceeded onl y by CABMV. Isolates of the unknown potyvirus were seedborne in Senega l cowpea lines and were nonpersistently transmitted by the cowpea aphi d, Aphis craccivora. Selected seedborne isolates of this potyvirus wer e distinguishable principally by differentially resistant cowpea genot ypes and by either weak (isolate V1-1) or strong (isolate V17-14) reac tions to potyvirus-selective monoclonal antibodies. Of 35 cowpea genot ypes tested as possible sources of resistance to the unknown potyvirus , six (TVU-401, TVU-408P2, TVU-1000, TVU-1016-1, TVU-1582, and White A cre-BVR) were resistant to all isolates of the virus. These genotypes have been included in the Senegal cowpea breeding program for developm ent of virus-resistant cultivars.