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Factors Affecting the Development of Head Smut Caused by Sphacelotheca reiliana on Corn. Carl A. Matyac, Department of Plant Pathology, University of Minnesota, St. Paul 55108; Thor Kommedahl, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Phytopathology 75:577-581. Accepted for publication 10 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-577.

Silty and sandy loam soils containing spores of Sphacelotheca reiliana were allowed to dry to matric potentials of - 0.1, - 0.5, or - 1.5 bar before resaturation and were held at 25, 20, 15 or 10 C in flats. A greater percentage of corn seedlings were diseased at high soil temperatures and low matric potentials than at low temperatures and high matric potentials. Teliospores on agar, adjusted with NaCl to decrease the osmotic potential, germinated at rates of 22% at solute potentials of - 22 bars and 78% at solute potentials close to zero. Field plots that received irrigation water had 22% smutted plants which was significantly less than that in the dry soil plots which had 30% diseased plants. In microplots, clay loam soils maintained higher matric potentials than silty or sandy loam soils and had 10% fewer smutted plants. Applications of urea, ammonium sulfate, and triple superphosphate significantly reduced the frequency of disease in field plots, whereas the addition of calcium nitrate caused slight but nonsignificant increases. There was no difference in the frequency of smutted plants when seed was planted at depths of 2.5 or 8.0 cm.