Factors Affecting the Infection of Fruit of Vitis vinifera by the Bitter Rot Pathogen Greeneria uvicola

Bitter rot, caused by the fungus Greeneria uvicola, is one of the most important fruit rot diseases that threaten the burgeoning winegrape (Vitis vinifera) industry in the southeastern United States. Epidemiological studies were conducted to examine the period of fruit susceptibility of V. vinifera to G. uvicola, influence of temperature and duration of wetness on infection, and relative susceptibility of cultivars to bitter rot. In field studies, susceptibility of Merlot, Chardonnay, and Cabernet Franc fruit increased from bloom until véraison in 2003 and from bloom until 2 weeks before véraison in 2004. When detached V. vinifera fruit were inoculated and incubated at 14, 22, 26, and 30°C for 6, 12, 18 or 24 h of wetness, 22.4 to 24.6°C and 6 or 12 h of wetness were the optimal conditions for infection of fruit by G. uvicola. The relative susceptibility of 38 cultivars and selections, including 23 V. vinifera cultivars and five French-American hybrids, was determined in a detached fruit inoculation assay. A wide range in susceptibility was observed among the cultivars and selections. Fruit of cultivars of V. vinifera were significantly more susceptible than French-American hybrids. Isolates of G. uvicola differed in aggressiveness when tested on cv. Chardonnay.