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Physiology and Biochemistry

Photosynthesis, Transpiration, and Water Use Efficiency of Mature Grape Leaves Infected with Uncinula necator (Powdery Mildew). A. N. Lakso, Associate professor, New York State Agricultural Experiment Station, Geneva 14456; Charlotte Pratt(2), R. C. Pearson(3), R. M. Pool(4), R. C. Seem(5), and M. J. Welser(6). (2)Senior research associate, New York State Agricultural Experiment Station, Geneva 14456; (3)(5)Associate professors, Department of Plant Pathology, New York State Agricultural Experiment Station, Geneva 14456; (4)Associate professor, New York State Agricultural Experiment Station, Geneva 14456; (6)Research technician, Department of Pomology and Viticulture, New York State Agricultural Experiment Station, Geneva 14456. Phytopathology 72:232-236. Accepted for publication 8 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-232.

Photosynthesis and transpiration of mature leaves of susceptible Vitis vinifera ‘White Riesling’ and less susceptible V. labruscana ‘Concord’ were related to levels of infection by Uncinula necator that developed in the field. Photosynthetic rate was reduced more in White Riesling than in Concord at similar levels of U. necator infection and of U. necator-induced tissue necrosis, due primarily to greater palisade layer destruction in White Riesling than in Concord leaves. Because transpiration was relatively unaffected by infection, water use efficiency in both cultivars decreased with increasing infection. In Concord, visual ratings of tissue necrosis provided better estimates of photosynthesis reduction than did visual ratings of U. necator infection. In White Riesling, both methods gave similar estimates of damage.