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 gener ation seed were planted in insect-free greenhouses at two locations an d resulting seedlings were assayed by direct antigen coated enzyme-lin ked immunosorbent assay (DAC-ELISA) for the presence of eight seedborn e viruses. By visual selection and DAC-ELISA, 10 virus-free mother pla nts 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 we re observed and tested by DAC-ELISA and were found to have remained fr ee from viruses during this field exposure. One or more of the followi ng viruses were detected in 40 of the 60 preintroductions: 32 containi ng cowpea aphid-borne mosaic potyvirus (possibly blackeye cowpea mosai c potyvirus in some cases); 23 with cowpea severe mosaic comovirus; 22 with southern bean mosaic sobemovirus; seven with cucumber mosaic cuc umovirus; 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 see dborne viruses. Virus-free experimental seed lots were produced for li mited use by interested cowpea breeders.