Influence of Connecticut temperatures on the relative pathogenicity of Maine and Connecticut verticillium isolates

Summary

The differential influence of temperature on growth of microsclerotial (M) and dark mycelial (D) types ofVerticillium albo-atrum Reinke and Berth is evidently responsible for the predominance of the M type in Connecticut. The D type, typical of Maine and other northern regions, is repressed in growth by temperatures of 83 F. No disease resulted from inoculation with a typical D isolate in the Connecticut field, whereas plants inoculated with an M isolate, typical of Connecticut, were sufficiently diseased to cause a significant reduction in yield. The temperatures in July and August, particularly the average maximum temperatures of 80 F to 85 F, apparently prevent the D type from causing disease in Connecticut.