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Ecology and Epidemiology

Nitrogen Effects on the Pathogenicity of Drechslera sorokiniana and Curvularia geniculata on Germinating Seed of Festuca rubra. James P. Madsen, Graduate research assistant, Department of Horticulture, Iowa State University, Ames 50011; Clinton F. Hodges, professor of Horticulture and of Plant Pathology, Department of Horticulture, Iowa State University, Ames 50011. Phytopathology 70:1033-1036. Accepted for publication 30 April 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-1033.

The effects of (NH4)2SO4 and Ca(NO3)2 on the pathogenicity of Drechslera sorokiniana and Curvularia geniculata, singly and in combination on germinating seed of Festuca rubra were evaluated. Both nitrogen sources at 102M reduced the rate of seedling emergence and total emergence from uninoculated seed in autoclaved and nonautoclaved soil. Total seedling emergence from uninoculated seed in nonautoclaved soil was less than that in autoclaved soil in response to both nitrogen sources at 102 M. These responses were suggestive of direct nitrogen toxicity to the germinating seed in autoclaved soil and of stimulation of unknown biotic factors in nonautoclaved soil that, when combined with direct nitrogen toxicity, additively reduced total emergence. A concentration of 103 M of both nitrogen sources generally stimulated rate of seedling emergence and had no effect on total seedling emergence from uninoculated seed. The lowest concentration (104M) of the nitrogen sources tested showed mixed effects on rate of seedling emergence and total emergence from uninoculated seed in autoclaved and nonautoclaved soil. The highest concentration of both nitrogen sources enhanced the pathogenicity of D. sorokiniana and C. geniculata, inoculated on seed both alone and in combination. Rate of seedling emergence was slowed by D. sorokiniana and the combination of D. sorokiniana + C. geniculata, and each pathogen and their combination also reduced total seedling emergence. The combination of the pathogens, together with the highest concentration of either nitrogen source, produced the most severe reduction in total seedling emergence. These results suggest a combination of direct toxicity to germinating seed and an enhancement of the pathogenicity of D. sorokiniana and C. geniculata induced by nitrogen-containing compounds.