VIEW ARTICLE

Ecology and Epidemiology

Environmental Influences on the Development of Puccinia helianthi on Sunflower. D. Shtienberg, Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel; H. Vintal, Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel. Phytopathology 85:1388-1393. Accepted for publication 23 August 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-1388.

Nine epidemics of rust, caused by Puccinia helianthi, on sunflower (Helianthus annuus) were analyzed concurrently. Although the epidemics occurred over a period of 3 years (1991 to 1993) and in three growing regions, the apparent infection rates were relatively uniform (average rate ± standard error = 0.237 ± 0.007). The possibility of using this rate to predict disease progress at an early stage of an epidemic was evaluated in four fields during 1994. In general, the extrapolated apparent infection rate was very close to the observed. To understand the biological basis for relatively uniform rates of disease increase, effects of environmental parameters on components of the life cycle of P. helianthi were examined. Urediniospore germination occurred at temperatures of 4 to 20șC, lasted 4 to 6 h, and required 6 to 10 h of leaf wetness. At 15 to 25șC, the time from inoculation until the appearance of the first pustule was 8 to 10 days. The minimum, optimum, and maximum temperatures for infection were 4, 10 to 24, and 30șC, respectively. Sporulation occurred over a wide range of temperatures (4 to 39șC); the optimum was between 20 and 35șC. On the basis of these findings, it was concluded that during the period of rust epidemics in Israel (May through June), the environment is rarely nonconducive to P. helianthi development.