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Multiplication and Pathogenesis of Cowpea Chlorotic Mottle Virus and Southern Bean Mosaic Virus in Single and Double Infections in Cowpea. C. W. Kuhn, Department of Plant Pathology and Plant Genetic, University of Georgia, Athens 30602; Wm. O. Dawson, Department of Plant Pathology and Plant Genetic, University of Georgia, Athens 30602, Present address of second author: Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 63:1380-1385. Accepted for publication 25 April 1973. DOI: 10.1094/Phyto-63-1380.

A mixed infection of cowpea chlorotic mottle virus (CCMV) and southern bean mosaic virus-cowpea strain (SBMV) caused a synergistic reduction of cowpea growth. Leaf, stem, and root weights; plant height; and yield were reduced more by a double infection than the additive effects of each single infection. The double infection increased seed transmission of SBMV from 12% to 20%. Viral nucleoprotein measurements demonstrated that a simultaneous inoculation of both viruses reduced the yield of SBMV about 50% but had no effect on the yield of CCMV. When either virus became established first and was in the rapid synthesis phase, the synthesis of the challenging virus was significantly retarded. Once past the rapid synthesis phase, synthesis of either virus in challenged plants was similar to synthesis in healthy plants of the same age. Smaller quantities of each virus were produced in new trifoliolate leaves, but a 1:3 ratio of CCMV: SBMV nucleoprotein was generally evident, indicating that neither virus became dominant in a double infection.

Additional keywords: necrosis symptoms, radioisotope labeling.