East African strains of cowpea aphid‐borne mosaic virus

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Abstract
SUMMARY: Cowpea aphid‐borne mosaic virus (CAMV) was isolated for the first time in East Africa where three distinct strains, type, veinbanding and mild, were differentiated by host range and serology. The three strains infected 17/38, 18/37 and 10/35 legume species, and 11/21, 7/21 and 3/19 non‐legume species, respectively.The viruses were propagated in cowpea and assayed in Chenopodium amaranticolor. Isolates of all three strains had similar in vitro properties: dilution end point between 10‐3 and 10‐4; thermal inactivation point between 56 and 58 °C; longevity in vitro between 2 and 3 days. Infectivity of sap from frozen leaves was high after 4 wk but much less after 7 wk; infectivity was largely precipitated by 50% acetone but inactivated by 50% ethanol. High yields of virus were consistently obtained from cowpea by extracting systemically infected leaves in 0.5 m sodium citrate containing 1% mercaptoethanol (pH 8.1), and clarifying with 8.5 ml n‐butanol/100 ml sap. Virus preparations contained numerous unaggregated and aggregated virus particles c. 750 nm long and contained components with sedimentation coefficients (s°20, w) of 150S and 175S (presumably unaggregated and aggregated particles, respectively). CAMV is serologically distantly related to bean common mosaic virus, but not to bean yellow mosaic or eight other morphologically similar viruses. It is a typical but distinct member of the potato virus Y group.