VIEW ARTICLE

The Effect of Temperature on the Pathogen and on the Development of Blue Mold Disease in Tobacco Inoculated with Peronospora tabacina. J. Rotem, The Volcani Institute of Agricultural Research, Bet Dagan, Israel; Y. Cohen, The Volcani Institute of Agricultural Research, Bet Dagan, Israel. Phytopathology 60:54-57. Accepted for publication 23 July 1969. DOI: 10.1094/Phyto-60-54.

The highest degree of sporulation and colonization of Peronospora tabacina was found at 15 to 20 C. At constant temperatures, the optimum development of disease occurred at 25 C, and under 12-hr periods of 20-C night and 20 to 40-C day temperatures, at 20-25 C. Shortening the length of high temperature periods during the daytime resulted in a shift of the optimal disease development to 30-35 C in plants exposed to those temperatures for 2 hr/day. Exposure of previously infected but still symptomless plants to temperatures lethal for the fungus, i.e., up to 45 C, induced development of sterile lesions within 24 hr, with 35 C leading to the most accentuated lesions. It was concluded that the optimal development of disease is affected by much higher temperatures than the development of the pathogen; but, for the high temperatures to exert their effect, a certain extent of previous colonization at a temperature favorable for the pathogen is needed. Under these conditions, the disease develops whether the pathogen remains alive or dies.