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The Effect of Leaf Exudates on Blueberry Leaf Spot Caused by Gloeosporium minus. R. D. Milholland, Associate Professor of Plant Pathology, North Carolina State University, Raleigh, 27607. Phytopathology 60:635-640. Accepted for publication 31 October 1969. DOI: 10.1094/Phyto-60-635.

Stem and leaf flecks on the highbush blueberry (Vaccinium corymbosum) caused by Gloeosporium minus have previously been reported. In addition to these symptoms, G. minus produces large, brown, circular to irregular shaped lesions 5-10 mm in diam on blueberry leaves in the field, and is capable of causing a serious fruit rot of blueberries. Infection occurs through wounds or hydathodes. All blueberry varieties were susceptible to G. minus, but some are more resistant than others. Minimum, optimum, and maximum temperatures for growth in culture are 12, 30, and 36 C. The importance of leaf exudates in increasing the inoculum potential of G. minus on blueberry leaves is suggested. Lesions were larger near the hydathodes where high concentrations of carbohydrates were exuded, and in wound inoculations. High concentrations of glucose added to the inoculum increased the pathogenicity of G. minus. Inoculations with conidia suspended in distilled water resulted in small flecks.