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Virus Diseases of Cowpeas in Dryland and Irrigated Plots in Botswana. D. W. Burke, P. Ditshipi, and C. J. deMooy, Department of Agronomy, Botswana Cowpea Project, Colorado State University, Fort Collins 80523, and G. I. Mink, Washington State University, IAREC, Prosser 99350.  Plant Disease 70:801, 1986.  Accepted for publication 16 April 1986.  Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-801e.

In 1985, mosaic symptoms resembling those reported for cowpea aphid-borne mosaic virus (CAMV) occurred in seedlings from 41 of 291 cowpea (Vigna unguiculata (L.) Walp. subsp. unguiculata) accessions grown both in drought-stressed dryland and in sprinkler-irrigated plots at Sebele in southern Botswana.  Of 55 symptomatic seedlings assayed by indirect ELISA, 35 reacted with one to four anisera prepared against four potyviruses: CAMV, blackeye cowpea mosaic virus, and two strains of bean common mosaic virus.  None reacted by ELISA with 16 other legume virus antisera or by agar diffusion assay against cowpea yellow mosaic virus antiserum.  In dryland, where no aphids were seen, virus apparently did not spread from infected to healthy plants.  In irrigated plots, where aphids flourished, systemic mosaic or necrosis eventually developed in most plants.  Symptoms, serology, and epidemiology indicate that CAMV or related aphid-borne viruses caused most of the virus disease symptoms observed.  Absence of disease spread, except under the unusual circumstance of sprinkler irrigation, suggests that viruses may not be important in dryland cowpea culture in this semiarid region.