OBSERVATIONS ON A VIRUS DISEASE OF COWPEA IN TRINIDAD

Abstract

A mosaic of cowpea and asparagus‐bean ( Vigna unguiculata) is common in Trinidad. The same virus sometimes attacks Cajanus indicus, Crotalaria juncea, Glycine max, Phaseolus mungo and P. aureus , usually when growing near to infected cowpeas. Desmodium frutescens, Psophocarpus tetragonolobus, Sesbania speciosa, Vigna vexillata, Phaseolus trinervius and varieties of P. Iunatus are also susceptible to systemic infection. Most of the above give local lesions, which are the only symptoms produced on Canavalia ensiformis and Dolichos lablab. No infections were obtained on Phaseolus vulgaris , or on any plant outside the Leguminoseae. The virus is seed‐borne in asparagus‐bean, but apparently not in tested cowpea varieties. The leaf beetle Ceratoma ruficornis is a vector, and is probably largely responsible for spread in the field; Aphis medicaginis seems unable to transmit the disease. The thermal inactivation‐point of the virus is 66°C., its dilution end‐point 1: 100,000, and longevity in vitro over 20 days.