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

Cucumber mosaic virus (CMV) and Blackeye cowpea mosaic virus (BlCMV) interact synergistically in dually infected plants of cowpea (Vigna unguiculata subsp. unguiculata) to cause cowpea stunt disease, the most damaging viral disease of this crop in the U.S. Sources of resistance to BlCMV are known and are present in cultivars of cowpea such as Pinkeye Purple Hull-BVR. However, no sources of CMV resistance have been found previously in cowpea. In 1998, PI 441918, a cowpea line growing in regeneration plots, was observed to have few viral symptoms, was not infected with BlCMV, and had a low titer of CMV when tested using direct antigen coating-enzyme-linked immunosorbent assay (DAC-ELISA). In greenhouse tests, infection of PI 441918 with CMV resulted 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 the 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 infection rate with CMV. PI 441918 offers a high level of resistance to BlCMV and moderate resistance to CMV, which are important characteristics in a parental line to develop cultivars of cowpea resistant to cowpea stunt disease.