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Physiological Effects of Cephalosporium gramineum on Growth and Yield of Winter Wheat Cultivars. J. B. Morton, Department of Plant Pathology, Montana State University, Bozeman 59717, Current address of senior author: Cargill PAG Research, P.O. Box 146, Lubbock, TX 79408; D. E. Mathre, Department of Plant Pathology, Montana State University, Bozeman 59717. Phytopathology 70:807-811. Accepted for publication 1 March 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-807.

The pattern of stripe formation on Cephalosporium gramineum-infected flag leaves of the susceptible winter wheat cultivar Marias was closely correlated with depression of relative water content, stomatal conductance, net photosynthesis, and chlorophyll content based on measurements from paired healthy and infected plants in the field. Regression analysis indicated that all four physiological parameters were interrelated, providing evidence that stripe formation coincides with localized water stress, reduction in transpiration rate, suppressed photosynthetic activity, and loss of chlorophyll. Chlorosis around colonized vascular bundles is therefore attributed to effects of localized restriction of lateral H2O movement rather than to a readily diffusible toxin. The influence of pathogenesis on vegetative and reproductive growth patterns was measured during growth and development of three winter wheat cultivars, Marias, Crest LRC 40, and PI 278212. Internode elongation was inhibited, but leaf expansion remained unaffected by disease. Spikelet number was unaltered by disease, seed number was reduced in Marias and PI 278212, and thousand kernel weight was sharply reduced in Marias and PI 278212 but only moderately reduced in Crest LRC 40. Thus, the effects of pathogenesis are not pronounced until after anthesis during grain filling. Duration of photosynthesis, as measured by averaging CO2 exchange of 10 flag leaves of each cultivar for 35-days after anthesis, appeared to play a major role in seed weight reduction.