International Institute of Tropical Agriculture, Nigeria, and IITA/USAIDITanzania Research Project, Crop Research Division, Ministry of Agriculture, P.O. Box 9071, Dar es Salaam, Tanzania
*Present address: Department of Botany and Plant Sciences, University of California, Riverside, California 92521, U.S.A.
In screening of 249 cowpea (Vigna unguiculata (L.) Walp.) cultivars/germplasm lines by sap inoculations with veinbanding strain of the cowpea aphid-borne mosaic virus (CAMV) in pothouse and under natural epiphytotic in disease nursery, ten lines proved immune and eight were resistant. The remainder reacted as moderately resistant/moderately susceptible (12), delayed susceptible (30), susceptible to very susceptible (176) or heterogeneous (13). Comparison of the reactions in some lines also tested by others with CAMV strains from Nigeria, Kenya and U.S.A. showed Tanzania strain to be pathogenically distinct. Preliminary studies on inheritance indicated that immune reaction was controlled by a recessive gene in association with minor/modifier genes and the resistant reaction was governed by a partially dominant gene. In a breeding programme, using a CAMV resistant line TVu 410 (also moderately resistant to bacterial blight disease) and agronomically superior but CAMV susceptible cv. SVS-3, resistant derivatives were developed which outyielded SVS-3 in multilocation trial in Tanzania.
