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Effect of Powdery Mildew on Net Photosynthesis, Dark Respiration, and Kernel Composition of Pecan. T. R. Gottwald, Research Plant Pathologist, USDA-ARS, Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA 31008. B. W. Wood, Research Horticulturist, USDA-ARS, Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA 31008; and P. F. Bertrand, Extension Plant Pathologist, Rural Development Center, University of Georgia, Tifton 31794. Plant Dis. 68:519-521. Accepted for publication 12 January 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/PD-68-519.

Pecan foliage and fruit were studied to determine the effect of powdery mildew on net photosynthesis, dark respiration, and kernel composition. Powdery mildew had no effect on net photosynthesis or dark respiration of pecan fruit or on leaf respiration. Net photosynthesis of foliage was reduced as much as 42% by high disease levels (about 5476%). Powdery mildew covering 50% of the fruit surface area decreased percent kernel oil, protein, and free fatty acids by 3.8, 7.1, and 73.1%, respectively, and increased percent moisture by 3.4%. Heavy mildew (about 100% of the surface area infected) decreased percent kernel oil, protein, and free fatty acids by 8.6, 22.3, and 73.1%, respectively, and increased percent moisture by 13.6%.