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Effects of Acute Low-Temperature Events on Development of Erysiphe necator and Susceptibility of Vitis vinifera

First, second, third, fourth, sixth, and seventh authors: Department of Plant Pathology and Plant-Microbe Biology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; third author: United States Department of Agriculture–Agricultural Research Service Grape Genetics Research Unit, Geneva, NY 14456; fourth author: CSIRO Plant Industry, Glen Osmond, South Australia 5064, Australia and fifth author: Magarey Plant Pathology, Loxton, South Australia 5333, Australia.

Growth and development of Erysiphe necator (syn. Uncinula necator) has been extensively studied under controlled conditions, primarily with a focus on development of grapevine powdery mildew within the optimal temperature range and the lethal effects of high temperatures. However, little is known of the effect of cold temperatures (above freezing but <8°C) on pathogen development or host resistance. Pretreatment of susceptible Vitis vinifera leaf tissue by exposure to cold temperatures (2 to ≤8°C for 2 to 8 h) reduced infection efficiency and colony expansion when tissues were subsequently inoculated. Furthermore, nascent colonies exposed to similar cold events exhibited hyphal mortality, reduced expansion, and increased latent periods. Historical weather data and an analysis of the radiational cooling of leaf tissues in the field indicated that early-season cold events capable of inducing the foregoing responses occur commonly and frequently across many if not most viticultural regions worldwide. These phenomena may partially explain (i) the unexpectedly slow development of powdery mildew during the first month after budbreak in some regions and (ii) the sudden increase in epidemic development once seasonal temperatures increase above the threshold for acute cold events.

Additional keywords: induced resistance.