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Ecology and Epidemiology

Density Dependent Sporulation of Erysiphe graminis f. sp. tritici. D. I. Rouse, Department of Plant Pathology, University of Wisconsin, Madison 53706; D. R. MacKenzie(2), and R. R. Nelson(3). (2)Department of Plant Pathology and Crop Physiology, Louisiana State University, Baton Rouge 70803; (3)Department of Plant Pathology, Pennsylvania State University, University Park 16802. Phytopathology 74:1176-1180. Accepted for publication 25 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1176.

An exponential decrease in cumulative number of spores produced per colony as the number of colonies per primary leaf increased was observed for two isolates of Erysiphe graminis f. sp. tritici on plants of wheat cultivars Blueboy, Redcoat, and Knox. This relationship was observed beginning 8- 14 days after inoculation depending on cultivar and isolate. The magnitude of the effect of colony numbers per leaf on spores per colony was measured by the slope of the regression of the logarithm of cummulative spores per colony versus colonies per leaf. The slope increased until 20 days after inoculation when spore production ceased. With the exception of isolate 112 on Knox, maximum spore production per primary leaf occurred when there were ~25 colonies per leaf. Additional colonies per leaf resulted in decreased total spore production. Thus, a mechanism of density dependent regulation of growth of E. graminis f. sp. tritici is reduction in spore production per colony as the number of colonies per leaf increase. Since this relationship was different for different isolate-cultivar combinations, spore production per colony as a function of number of colonies per leaf should be considered as a possible component of rate reducing resistance.