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Oral: Population Dynamics


Epidemiology and Population Biology of Grape Downy Mildew (Plasmopara viticola) in Georgia
C. HONG (1), P. Brannen (1), H. Scherm (1) (1) University of Georgia, U.S.A.

The epidemiology of Plasmopara viticola has been studied extensively in temperate and Mediterranean climates, but limited information is available for the southeastern U.S. where hot and humid conditions may affect survival, disease progression, and population structure of the pathogen. Downy mildew epidemic progress was monitored in 2015 in a North Georgia Vitis vinifera vineyard on cultivars Merlot and Chardonnay. Disease onset was 2 months later than predicted by a mechanistic model for oospore germination and primary infection, highlighting knowledge gaps relative to epidemiological processes in Georgia conditions. Since timing of disease onset may be related to the mode of pathogen overwintering, pairings among single-sporangium isolates were conducted to determine the potential for sexual reproduction. Oospores were observed in about half of the pairings, indicating that both mating types are present. To better understand the relative contribution of sexual and asexual reproduction and to determine the population structure of the pathogen, isolates of P. viticola were collected from 19 grape varieties in 10 vineyards throughout Georgia. Initial genotyping of 96 isolates identified only one of the previously described five cryptic species of P. viticola, clade aestivalis. This study confirmed sexual reproduction, revealed preliminary pathogen population structure, and identified knowledge gaps regarding primary infection by P. viticola in Georgia vineyards.