Resistance to Cucumber mosaic virus in cowpea and implications for controlof cowpea stunt disease

Cucumber mosaic virus (CMV) and Blackeye cowpea mosaic virus (BlCNW) intera ct synergistically in dually infected plants of cowpea (Vigna unguiculata s ubsp. unguiculata) to cause cowpea stunt disease, the most damaging viral d isease of this crop in the U.S. Sources of resistance to BlCMV are known an d are present in cultivars of cowpea such as Pinkeye Purple Hull-BVR. Howev er, no sources of CMV resistance have been found previously in cowpea. In 1 998, PI 441918, a cowpea line growing in regeneration plots, was observed t o have few viral symptoms, was not infected with BlCMV, and had a low titer of CMV when tested using direct antigen coating-enzyme-linked immunosorben t assay (DAC-ELISA). In greenhouse tests, infection of PI 441918 with CMV r esulted in a lower titer of virus if the inoculated plants were from white seeds of PI 441918 than if the plants were from tan seeds of this PI, and a lower titer of virus than plants of the susceptible cultivar Coronet. In t he field, with CMV- and BlCMV-infected plants of Coronet in spreader rows, plants from white seed of PI 441918 had no infection with BlCMV and a low i nfection rate with CMV. PI 441918 offers a high level of resistance to BlCM V and moderate resistance to CMV, which are important characteristics in a parental line to develop cultivars of cowpea resistant to cowpea stunt dise ase.