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Production of Pseudothecia and Ascospores by Pyrenophora tritici-repentis in Response to Macronutrient Concentrations. W. F. Pfender, Assistant professor, Department of Plant Pathology, Kansas State University, Manhattan 66506; S. L. Wootke, Research assistant, Department of Plant Pathology, Kansas State University, Manhattan 66506. Phytopathology 77:1213-1216. Accepted for publication 24 March 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1213.

Pyrenophora tritici-repentis, causal agent of wheat tan spot, was grown on a medium consisting of purified cellulose moistened with an aqueous solution of nitrogen (urea or nitrate) and nutrient salts and incubated under conditions of light and temperature favorable for sexual reproduction. With adequate amounts of phosphorus and potassium, abundant pseudothecia formed at 900 ppm added N (micrograms of N per gram of dry cellulose), supplied as either urea or nitrate. At 90 ppm added N, pseudothecia production was reduced approximately 60%; at 9 ppm added N, only a few small pseudothecia formed. Ascospore production was proportional to N level, except for being inhibited by nitrate at 900 ppm. With urea at 900 ppm N, production of fertile pseudothecia responded to levels of P and K. With 200 ppm P and 500 ppm K, abundant fertile pseudothecia were produced. Reducing these levels 10-fold had no significant effect, but at 2 ppm P and 5 ppm K, few pseudothecia were produced and most were immature.