VIEW ARTICLE

Ecology and Epidemiology

Rhizosphere Competence of Trichoderma harzianum. Jaleed S. Ahmad, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523; Ralph Baker, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Phytopathology 77:182-189. Accepted for publication 28 April 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-182.

Rhizosphere competence of Trichoderma harzianum was measured for roots of bean, cucumber, maize, radish, and tomato. When seeds were coated with conidia of the wild type and germinated in soil under constant matric potential with no additional water added, the fungus was not detected in the rhizospheres of roots from 1- to 8-cm depths after 8 days. Mutants tolerant to benomyl, however, were rhizosphere-competent when 10 ?g of benomyl was added per gram of soil. These mutants were also rhizosphere-competent when benomyl was not added. The degree of rhizosphere colonization by mutants of T. harzianum was influenced by benomyl, soil pH, and temperature. Evidence provided herein indicates that a rhizosphere-incompetent biological control agent was induced by mutation to become rhizosphere-competent.