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Cowpea Stunt: Heterogeneous and Differential Reactions of Cowpea Cultivars. G. Pio- Ribeiro, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens, GA 30602, Present address of senior author: Departamento de Agronomia, Universidade Federal Rural de Pernambuco, Dois Irmaos, 50000 Recife, PE., Brazil; C. W. Kuhn, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens, GA 30602. Phytopathology 70:244-249. Accepted for publication 4 September 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-244.

Four major types of disease reactions were observed when 20 cowpea cultivars or test lines were inoculated with an inoculum mixture of cucumber mosaic virus (CMV) and blackeye cowpea mosaic virus (BlCMV): severe stunt, severe stunt with necrosis, delayed stunt with necrosis, and mild mottle (CMV only). Heterogeneous disease reactions occurred among plants in 10 of the cultivars; however, progeny from individual plants reacted homogeneously. All seed lots of all cultivars reacted homogeneously (mild mottle) to CMV alone. Although the 10 cultivars reacted heterogeneously to BlCMV alone, the reactions of the cultivars were more easily visualized when plants were inoculated with both viruses because of a synergistic interaction. The mild mottle reaction to mixed inoculum occurred on plants with a high degree of resistance to BlCMV. Seed lines selected for homogeneous reaction (susceptible or resistant) to BlCMV were used as a differential set of hosts to characterize three other isolates of BlCMV and two of cowpea aphid-borne mosaic virus (CAMV). Typical cowpea stunt reactions occurred with all BlCMV and CAMV isolates in inoculum mixtures with CMV; the type of reaction was dependent on the cultivar. It is concluded that either BlCMV or CAMV can be a virus component of cowpea stunt.