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Ecology and Epidemiology

The Competitive Saprophytic Ability of Sclerotium oryzae Derived from Sclerotia. W. W. Bockus, Graduate Research Assistant, Department of Plant Pathology, University of California, Davis, CA 95616; R. K. Webster(2), and T. Kosuge(3). (2)(3)Professors, respectively, Department of Plant Pathology, University of California, Davis, CA 95616. Phytopathology 68:417-421. Accepted for publication 14 September 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-417.

Radioactive (14C-labeled) sclerotia of Sclerotium oryzae were incubated in moist soil in petri dishes to determine their ability to produce new sclerotia saprophytically. Soil used for the study was from two locations on which rice had been grown for a number of years. Since the soils were infested with S. oryzae the naturally occurring sclerotia were removed by sieving before the introduction of labeled sclerotia. Treatments included both autoclaved and nonautoclaved soil, with or without an amendment of dried, noninfected, nonsterilized rice sheaths. Sclerotia produced in the soil by S. oryzae as a result of saprophytic colonization of organic material were not labeled and thus were distinguishable from the labeled sclerotia originally introduced. The saprophytic ability of S. oyrzae was too low to enable it to use residual organic material in either nonautoclaved or autoclaved soil. In autoclaved soil amended with rice sheaths the sclerotia germinated, the fungus colonized the sheaths, and the number of sclerotia increased. In nonautoclaved soil amended with rice sheaths a few new sclerotia were produced as a result of colonization of the sheaths but they did not contribute significantly to the population of sclerotia in the soil. In another experiment, nylon mesh bags filled with soil containing chopped rice sheaths and radioactive sclerotia were buried in moist field soil for 5 wk. No new sclerotia were recovered which were produced as a result of saprophytic colonization of the sheaths. The use of radiolabeled sclerotia, as described here, is considered a useful aid in following populations of sclerotia in the soil.

Additional keywords: rice stem rot, Magnaporthe salvinii.