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

Viral diseases of cowpea (Vigna unguiculata subsp. unguiculata) in Senegal were surveyed during the rainy seasons of 1990 and 1991. Sixty-six symptomatic plant samples from five production areas were assayed for seven viruses by enzyme-linked immunosorbent assay (ELISA). Four recognized viruses, cowpea aphid-borne mosaic potyvirus (CABMV), cowpea mottle carmovirus (CPMoV), cowpea severe mosaic comovirus (CSMV), and southern bean mosaic sobemovirus (SBMV), were detected in 34, 2, 1, and 1 samples, respectively. All are seed-transmissible in cowpea. Variants of an unknown potyvirus were also detected in 21 samples. These variants occurred principally in new, improved CABMV-resistant cowpea genotypes, and their combined incidence in plant samples was exceeded only by CABMV. Isolates of the unknown potyvirus were seedborne in Senegal cowpea lines and were nonpersistently transmitted by the cowpea aphid, Aphis craccivora. Selected seedborne isolates of this potyvirus were distinguishable principally by differentially resistant cowpea genotypes and by either weak (isolate V1-1) or strong (isolate V17-14) reactions to potyvirus-selective monoclonal antibodies. Of 35 cowpea genotypes tested as possible sources of resistance to the unknown potyvirus, six (TVU-401, TVU-408P2, TVU-1000, TVU-1016-1, TVU-1582, and White Acre-BVR) were resistant to all isolates of the virus. These genotypes have been included in the Senegal cowpea breeding program for development of virus-resistant cultivars.