Decreased Net Photosynthetic and Dark Respiration Rates of Pecan Fruit and Foliage in Response to Infection by Cladosporium caryigenum. 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. Plant Dis. 69:800-803. Accepted for publication 18 February 1985. 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, 1985. DOI: 10.1094/PD-69-800.

Pecan fruit and foliage with various intensities of pecan scab were studied to determine the effect of scab on net photosynthetic rate and dark respiration. Low disease intensities (about 5–30% of fruit surface area infected) caused decreases of 83 and 49%, respectively, in net photosynthetic rate (NPR) and dark respiration rate (DRR). Additional disease increase (beyond 30% of fruit surface area infected) caused further reductions of 5 and 3%, respectively, in NPR and DRR. Nut surface area of fruit infected in mid-August decreased linearly with percent disease at a rate of 1:5.26 (percent disease in nut surface area:percent disease increase). Reduction in foliar NPR was roughly proportional to the amount of foliar surface area colonized. Thus, lesions covering 10% of the phylloplane caused about 10% reduction in NPR. Leaf area was also diminished by disease at a rate of 22% per lesion per square centimeter of leaf surface.