SURVEY ON COWPEA VIRUS INCIDENCE AND DISTRIBUTION IN NIGERIA

Enzyme-linked immunosorbent assay (ELISA) was used to detect viruses i n 649 cowpea leaf samples collected from 115 fields during a 3-year su rvey carried out from 1991 to 1993 throughout all agroecological zones in Nigeria. Six viruses, cowpea aphid-borne mosaic potyvirus (CAMV), blackeye cowpea mosaic potyvirus (BICMV), southern bean mosaic sobemov irus (SBMV), cowpea mottle carmovirus (CMoV), cowpea (yellow) mosaic c omovirrs (CpMV) and the cowpea strain of cucumber mosaic cucumovirus ( CMV-CS) were detected in 390 out of the 649 samples assayed. There was considerable variation in both disease incidence and virus distributi on in the different crop habitats within and between seasons. Thus, wh ile SBMV had the highest incidence (27.4%) and was the most prevalent (66.7% in 1991, CAMV had the highest incidences (11.3% and 28.8%, resp ectively) and was the most prevalent 33% and 68%, respectively) in 199 2 and 1993. CpMV and CMoV remained consistently moderate both in incid ence and prevalence throughout the duration of the survey. The detecti on of the three beetle-transmitted spherical viruses (SBMV, CpMV and C MoV) in the Sudan and Sahel Savanna indicates that there is no ecologi cal restriction to the distribution of any of the viruses. Incidence o f multiple infection of up to four and five viruses in individual samp les was observed, but mixed infection with two viruses was more preval ent (13%). The potential for horizontal resistance breeding based on c ommon Vector transmission is discussed.