OCCURRENCE OF VERTICILLIUM-DAHLIAE ON SUNFLOWER (HELIANTHUS-ANNUUS) IN THE UK

In August 1994 verticilliosis-like symptoms were noticed in a maturing crop of sunflower at IACR-Rothamsted. Wilting plants with chlorotic a reas on some leaves, and dark areas of microsclerotia at the base of s tems, were first observed on 11 August. As the plants matured, dark st ripes were also observed on the stems. Many stems became brittle and l ater collapsed. Infected xylem showed a brown discolouration, later tu rning to black, and microsclerotia developed. Verticillium dahliae was isolated from an parts of the plant. In general, once symptoms were p resent, the incidence of verticilliosis-affected plants increased, and the disease developed, more rapidly in early maturing varieties than in the later maturing types. At harvest, incidence ranged between 24.5 % and 89.8%, depending on variety. Early maturing varieties appeared t o be more susceptible than later maturing types. Isolates of V. dahlia e were cultured in the laboratory. Sunflower plants were artificially inoculated with these isolates and developed verticilliosis symptoms w hen grown under controlled environmental conditions.