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Ecology and Epidemiology

Effects of Free Moisture, Head Development, and Embryo Accessibility on Infection of Wheat by Ustilago tritici. R. Loria, Former graduate research assistant, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824, Present address: Assistant professor, Department of Plant Pathology, Cornell University, Long Island Horticultural Research Laboratory, Riverhead, NY 11901; M. V. Wiese(2), and A. L. Jones(3). (2)(3)Former associate professor, and professor, respectively, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824; (2)Present address: Professor Department of Plant and Soil Science, University of Idaho, Moscow 83843. Phytopathology 72:1270-1272. Accepted for publication 4 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1270.

Varying the concentration of teliospores in a spore-talc mixture from 0.02 to 20% did not alter infection of intact florets by Ustilago tritici. Florets inoculated during anthesis were 3.13.8 times more susceptible than those inoculated before or after anthesis. Infection of florets was 18.5 and 22.9% for free-moisture periods of 8 and 32 hr, respectively; but was also relatively high (12.3%) with no wetting period. When glumes were clipped to improve floret accessibility, mean infection was 13.631.4% compared to 1.111.9% for intact florets. Teliospore germination inside and outside florets increased with ambient relative humidity, but germination was higher inside than outside florets at the two highest relative humidities. Embryo accessibility appears to be a limiting factor in infection of wheat by U. tritici.

Additional keywords: epidemiology, loose smut of wheat, Triticum aestivum.