REACTION OF COWPEA (VIGNA-UNGUICULATA L. WALP.) TO 6 ISOLATES OF BLACKEYE COWPEA MOSAIC-VIRUS (BICMV) AND COWPEA APHID-BORNE MOSAIC-VIRUS (CAMV), 2 POTYVIRUSES INFECTING COWPEA IN NIGERIA

Five potyvirus isolates from various cowpea-producing areas (Guinea an d Sudan savannas and forest zones) in Nigeria were identified by serol ogy and infectivity tests as BICMV (Isolates IT15, IT16 and WC) or as CAMV (isolates IT11 and ZARIA) and compared with the standard isolate of blackeye cowpea mosaic virus (BICMV) (isolate ONNE) used at the Int ernational Institute of Tropical Agriculture (IITA) for screening purp oses. According to the type and severity of symptoms on Nicotiana bent hamiana and on selected susceptible cowpea cultivars, the BICMV and CA MV isolates studied were grouped into three categories. Members of the first group (isolates IT15 and IT16) induced mild-to-severe bright ye llow mosaic on selected susceptible cowpea cultivars and could not eas ily infect Nicotiana benthamiana, but the other two groups of isolates readily infected this plant. In the second group of isolates, ONNE an d WC induced mosaic with variable severity in dark green and yellow pa tches. The third group (isolates IT11 and ZARIA) induced mild green mo saic and veinbanding symptoms on different cowpea lines. An evaluation of cowpea germplasm accessions and breeding lines using these BICMV a nd CAMV isolates has shown that germplasm accessions TVu 401, TVu 1453 and TVu 1948 and breeding lines IT82D-885, IT82D-889 and IT82E-60 pos sess resistance genes to all six potyvirus isolates. These lines could be used in breeding programs at IITA to develop new cowpea varieties.