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Effects of Temperature, Soil Moisture, and Wheat Bran on Growth of Trichoderma harzianum from Alginate Pellets. G. R. Knudsen, Assistant professor, Plant Pathology Division, Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow 83843; Li Bin, Graduate research assistant, Plant Pathology Division, Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow 83843. Phytopathology 80:724-727. Accepted for publication 31 January 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-724.

Radial growth rates and hyphal densities were quantified for hyphae originating from alginate pellets containing hyphae of the biocontrol fungus Trichoderma harzianum. Pellets containing 1.8 mg of hyphal biomass (mean dry weight) and either 0 or 2.5 mg of wheat bran were buried beneath sheets of nylon mesh in a steamed silt loam soil, then incubated at 15, 20, or 25 C and –0.03, –0.1, or –0.5 MPa soil matric potential. Extent of hyphal growth was visually mapped after 0, 1, 2, 3, 5, 7, and 14 days, and mean radii were calculated from digitized maps. A visual assessment key for hyphal density was developed with a computer graphics program. With the key, hyphal density at 5, 10, 20, 30, and 40 mm from pellets was quantified after 7 and 14 days. For radial extension of hyphae, a logistic growth model was fit, with the assumption of a 24-hr lag (“germination”) period (mean R2 for all treatments = 0.71). Multiple regression of environmental variables against the slope of each growth curve showed that temperature had a significant positive effect on radial growth rate but that matric potential and bran effects were not significant. Hyphal density declined exponentially with distance from pellets. Hyphal density was significantly higher with bran, in drier soil, and after 14 versus 7 days. Temperature did not significantly affect hyphal density at 7 or 14 days. Methods and results presented may be useful for comparison of nutritional additives or other formulations for pelletized biocontrol fungi or as a basis to develop predictive models for performance of pelletized biocontrol fungi at different application rates and under varying environmental conditions.