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Influence of Temperature and Wetting Period on Inoculum Production by Monilinia fructicola in Peach Twig Cankers

Overwintering cankers in peach twigs caused by the brown rot fungus, Monilinia fructicola, were studied to identify the relationships of wetting period and temperature on sporulation. Sporulation was observed on blighted blossoms, peduncles, abscission scars, and cankers resulting from contact with infected fruits. The frequency of sporulation on overwintered infected tissues was greater at 15 and 23°C than at 4 or 11°C. Twelve hours of wetting was sufficient at all temperatures studied (5 to 23°C) for sporulation to occur, but the number of twig cankers supporting sporulation increased with time of wetting up to 72 h. Given the additional moisture requirements for spore germination, ingress, and infection, 17 to 30 h of wetting or high humidity during bloom may be needed for blossom blight to occur unless viable conidia are already present as a result of previous wetting periods.