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Ecology and Epidemiology

Effects of Available Carbon Source on Microbial Activity and Suppression of Pythium aphanidermatum in Compost and Peat Container Media. R. Mandelbaum, Research assistant, Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, faculty of agriculture, P.O. Box 12, Rehovot, 76100 Israel; Y. Hadar, senior lecturer, Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, faculty of agriculture, P.O. Box 12, Rehovot, 76100 Israel. Phytopathology 80:794-804. Accepted for publication 6 February 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-794.

Incorporation of a glucose/asparagine mixture of 10 carbon units to each nitrogen unit (C:N ratio = 10:1) into container media resulted in a rapid increase in microbial respiration rate and enzymatic activity in composted, separated, cattle-manure medium, but not in peat or limed peat media. Respiration was increased with an increase in ambient temperature. Glucose was depleted much faster in compost medium than in peat media. Compost medium amended with glucose/asparagine was more conducive to bacterial growth than peat media and less conducive to fungal growth. Hyphae of Pythium aphanidermatum grown on nylon fabric and buried in container media were rapidly lysed in compost medium as compared with peat-based media. Glucose/asparagine amendment delayed hyphal lysis of Pythium. Light and scanning electron microscopy of hyphae of Pythium retrieved from container media showed no evidence of direct parasitism on hyphae by other soil fungi; however, bacteria were associated with the lysing hyphae. Oospores of Pythium supported on nylon fabric and buried in container media were not lysed, nor did their viability differ in the different media. Amendment of glucose/asparagine to container media resulted in an increase in disease incidence; however, only after several consecutive amendments of glucose/asparagine to compost medium was suppression of Pythium damping-off negated.