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Factors Affecting Trichoderma hamatum Applied to Seeds as a Biocontrol Agent. G. E. Harman, Associate professor, Department of Seed and Vegetable Sciences, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; I. Chet(2), and R. Baker(3). (2)Professor, Department of Plant Pathology and Microbiology, the Hebrew University of Jerusalem, Rehovot, Israel; (3)Professor, Department of Botany and Plant Pathology, Colorado State University, Fort Collins 80523. Phytopathology 71:569-572. Accepted for publication 12 November 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-569.

Trichoderma hamatum, applied as a seed treatment, controlled seed rot of pea or radish in soil infested with Pythium spp. or Rhizoctonia solani, respectively, if soil temperatures were between 17 and 34 C and seeds had been treated with a suspension of conidia with a concentration equal to or greater than 106/ml. Addition of chitin or cell walls of R. solani to seed coats increased the ability of the mycoparasite T. hamatum to protect seeds against Pythium spp. or R. solani and resulted in an increase in the population density of Trichoderma in the soil. T. hamatum with chitin, but not with cell walls of R. solani, effectively reduced damping-off resulting from Pythium spp. compared with a seed treatment containing only T. hamatum. Addition of peat to T. hamatum did not increase the protective ability of the agent as a seed treatment, but resulted in an increase in its population density in soil. Addition of a nonpathogenic isolate of R. solani had little effect either on protection of seeds or levels of Trichoderma in the soil, whereas addition of cellulose tended to decrease both protection and establishment of the biocontrol agent in the soil. Treatment of seeds with both Rhizobium and T. hamatum had no effect on the nodulating activity of the former or the protective ability of the latter.