VIEW ARTICLE

Ecology and Epidemiology

Nutritional Factors Affecting Responses of Sporangia of Pythium ultimum to Germination Stimulants. Eric B. Nelson, Associate professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853; Jean S. T. Hsu, research support specialist, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853. Phytopathology 84:677-683. Accepted for publication 29 March 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-677.

Our study was designed to examine nutritional factors regulating germination of Pythium ultimum sporangia in response to glucose and seed-exudate stimulants. As mycelial cultures aged on media containing soybean lecithin, glucose-responsive germination of sporangia produced from these mycelia increased from less than 5% at 4 days to nearly 100% at 14 days. Responses of sporangia to cotton and cucumber seed exudate also increased during the 14-day period. Mycelial cultures growing on living plant tissue gave rise to sporangia unresponsive to glucose or cotton seed exudate after 14 days. By 18 days, these sporangia were sensitive only to seed exudate. Growth of mycelial cultures on media containing decreasing levels of various nutrients gave rise to sporangia with increasing sensitivity to seed exudate. Germination of sporangia in response to glucose remained low regardless of the concentration of most nutrients in the medium. Decreasing levels of lecithin in the medium, however, increased the response of sporangia to glucose. As sporangia aged from 4 to 15 days, germination responses to glucose, as well as to both cucumber and cotton seed exudates, increased. Results suggest that nutrient deprivation can qualitatively and quantitatively affect responses of sporangia to germination stimuli.