Role of Conidia ofBotryosphaeria dothideain the Natural Spread of Peach Tree Gummosis

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Abstract
Symptoms of peach (Prunus persica) tree gummosis were visible 9-13 mo. after healthy limbs were exposed for 30 day periods to conidia of B. dothidea produced on naturally infected peach wood. Experimental inoculations in July caused significantly more infections than those in March, April or May. Branches inoculated in June with a suspension of conidia had symptoms after only 3 mo. Swollen lenticels and sunken lesions developed on 1 or 2 yr old branches; only sunken lesions formed on 3 yr old branches. Conidia were first detected in rainwater traps on March 22, and the greatest numbers were collected in late July and early Aug. 1977. Numbers of conidia declined in Dec. and none were detected in rainwater after Dec. 30. The rainwater collection from limbs diseased for 1-2 yr yielded 2-138 times as many conidia as limbs diseased for 4-5 yr. The optimum temperatures for germination and germ-tube growth of conidia obtained from diseased wood or agar cultures were 25-35.degree. C, respectively. Warm wet weather favored the release and germination of conidia that infected peach bark through lenticles and induced gummosis symptoms.

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