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The Effect of Temperature on Sporulation and Viability of Isolates of Peronospora Tabacina Collected in the United States. M. A. Moss, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; C. E. Main, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 78:110-114. Accepted for publication 1 August 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-110.

Field epidemics of tobacco blue mold recently occurred in the United States during periods of high summer temperature previously considered limiting to disease development. The effects of maximum day/night temperatures on sporulation and spore viability of isolates of Peronospora tabacina were determined in growth chamber studies. P. tabacina produced viable, infectious sporangiospores when developing lesions were exposed to day/night temperatures up to 36/25 C for 48 hr. Significantly fewer spores were produced at high temperatures compared to optimum conditions; however, such sporangia could be important as secondary inoculum for subsequent disease development should or when optimum field conditions return during the season. Maximum temperature levels reported for North American isolates in the literature before 1979 were 27-32 C. Isolates tested in this study appeared to be more temperature-tolerant.