Increased Growth of Plants in the Presence of the Biological Control Agent Trichoderma harzianum. Ya- Chun Chang, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Yih-Chang Chang, and Ralph Baker, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523; and Ofer Kleifeld and Ilan Chet, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76-100, Israel. Plant Dis. 70:145-148. Accepted for publication 3 August 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-145.

The potential of Trichoderma harzianum to induce increased growth of various floricultural and horticultural crops was determined. In raw soil containing the fungus, pepper seed germinated 2 days earlier than untreated controls. Steamed or raw soil infested with T. harzianum hastened flowering of periwinkle, increased the number of blooms per plant on chrysanthemums, and increased the heights and weights of other plants. Responses occurred consistently at population densities of T. harzianum higher than 10⁵ colony-forming units per gram of soil when the fungus was applied either in conidial suspensions or in a peat-bran mixture. Such population densities can be achieved economically by applying the agent to propagative beds, where rooted cuttings (e.g., chrysanthemum) may carry over adequate numbers of thallus units to ensure favorable growth responses after transplanting.