Abstract
Results are presented from greenhouse screening of 562 cowpea germplasm accession for resistance to two isolates of cowpea mottle virus (CMeV). Tolerance (predominantly symptomless, systemic infection) was the only type of virus resistance identified, though three levels of tolerance were distinguished. These were 'high tolerance' (symptomless infection), 'tolerance' (the occasional development of mild systemic symptom·) and 'hypersensitive tolerance' (necrotic local lesion development, accompanied by mild systemic symptoms). Neither true hypersensitivity nor immunity (symptomless reactions without virus retrieval) to CMeV was found, although three lines were immune to one isolate. More than 50 lines were identified as possessing resistance to both isolates and of these, five were found to possess resistance in experiments done by other workers with other isolates of CMeV. Nineteen of these CMeV tolerant lines additionally possess resistance to other cowpea viruses, including seven lines which combine resistance to cowpea (yellow) mosaic, cowpea aphid-borne mosaic and southern bean mosaic viruses. These multiple virus resistant genotypes are being used as disease resistant donors in the IITA cowpea improvement programme.
