Survey on cowpea virus incidence and distribution in Nigeria

Abstract

Enzyme-linked immunosorbent assay (ELISA) was used to detectviruses in649 cowpea leafsamples collectedfrom115 fields during a 3-year survey 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 sobemovirus (SBMV), cowpea mottle carmovirus (CMoV), cowpea (yellow) mosaic comovirus (CpMV) and the cowpea strain of cucumbermosaic cucumovirus (CMV-CS)were detectedin 390 outofthe 649 samples assayed. There was considerable variation in both disease incidence and virus distribution in the different crop habitats within and between seasons. Thus, while 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%, respectively) and was the most prevalent 33% and 68%, respectively) in 1992 and 1993. CpMV and CMoV remained consistently moderate both in incidence and prevalence throughout the duration of the survey. The detection of the three beetletransmitted sphericalviruses (SBMV, CpMV and CMoV)in the Sudanand Sahel Savanna indicates that there is no ecological restriction to the distributionofanyoftheviruses.Incidence ofmultipleinfectionofuptofour and five viruses in individual samples was observed, but mixed infection with two viruses was more prevalent (13%). The potential for horizontal resistance breeding based on common vector transmission is discussed.