SEED-BORNE VIRUSES IN PREINTRODUCTION COWPEA SEED LOTS AND ESTABLISHMENT OF VIRUS-FREE ACCESSIONS

Seeds from 60 cowpea preintroductions from Botswana, India, and Kenya were increased at the University of California Riverside. Second generation seed were planted in insect-free greenhouses at two locations and resulting seedlings were assayed by direct antigen coated enzyme-linked immunosorbent assay (DAC-ELISA) for the presence of eight seedborne viruses. By visual selection and DAC-ELISA, 10 virus-free mother plants for each of the 60 accessions were established. The seedlots from these mother plants were subsequently planted in isolation plots at St. Croix, Virgin Islands. Seedlings from the St. Croix seed increase were observed and tested by DAC-ELISA and were found to have remained free from viruses during this field exposure. One or more of the following viruses were detected in 40 of the 60 preintroductions: 32 containing cowpea aphid-borne mosaic potyvirus (possibly blackeye cowpea mosaic potyvirus in some cases); 23 with cowpea severe mosaic comovirus; 22 with southern bean mosaic sobemovirus; seven with cucumber mosaic cucumovirus; and seven with cowpea mottle carmovirus. None were found to contain ELISA-detectable cowpea mosaic comovirus or cowpea mild mottle carlavirus. Twenty preintroductions were free of ELISA-detectable seedborne viruses. Virus-free experimental seed lots were produced for limited use by interested cowpea breeders.