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A Mechanism for Increased Plant Growth Induced by Trichoderma spp.. M. T. Windham, Visiting assistant professor, Plant Pathology and Weed Science Department, Colorado State University, Fort Collins 80523, Present address: Department of Entomology and Plant Pathology, University of Tennessee, Knoxville 37916; Y. Elad(2), and R. Baker(3). (2)(3)Visiting assistant professor, and professor, respectively, Plant Pathology and Weed Science Department, Colorado State University, Fort Collins 80523, (2)Present address: Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Rehovot 76100 Israel. Phytopathology 76:518-521. Accepted for publication 26 November 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-518.

Enhanced plant growth resulting from amendments of soil with Trichoderma harzianum and T. koningii was investigated to determine if increased growth could be attributed to a direct effect of these Trichoderma spp. on the plant or a secondary effect due to control of minor plant pathogens. Addition of Trichoderma spp. to autoclaved soil increased rate of emergence of tomato and tobacco seedlings over that of the controls. Eight weeks after planting, root and shoot dry weights of tomato and tobacco were increased 213-275 and 259-318%, respectively, over the controls. When population densities of soil microflora (other than Trichoderma spp.) were determined, no quantitative and qualitative differences were observed between soils infested with Trichoderma spp. and the controls. When soil fertility was increased, the level of increased tomato growth induced by Trichoderma spp. was enhanced. Radish plants grown in gnotobiotic conditions with T. harzianum T-95 were larger than radish plants grown under similar conditions without the agent. The rate of seed germination was increased compared with controls where Trichoderma spp. were not present when seeds were separated from Trichoderma spp. by a cellophane membrane. We conclude that these Trichoderma spp. produced a growth-regulating factor that increases the rate of seed germination and dry weight of shoots and stems.