RNA 2 of Red Clover Necrotic Mosaic Virus Determines Lesion Morphology and Systemic Invasion in Cowpea

Department of Pure and Applied Biology, Imperial College of Science and Technology, London SW7 2BB, U.K. Red clover necrotic mosaic virus (RCNMV) has two RNA species of mol. wt. about 1.5 x 10 6 (RNA 1) and 0.5 x 10 6 (RNA 2). An English strain (H) and a Czechoslovakian strain (TpM-34) of RCNMV could be distinguished serologically, by solid-phase RNA hybridization analysis (Northern blotting) and by the symptoms they induced in cowpea. Studies of pseudorecombinants, formed following inoculation of plants with heterologous combinations of the RNA species of each strain, showed that RNA 2 determines the morphology of lesions induced by the isolates in cowpea and their ability to invade the plants systemically. Keywords: RCNMV, pseudorecombinants, lesion morphology, systemic infection Received 22 August 1985; accepted 7 October 1985.