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Postulated Mechanism of Biological Control of Decay Fungi in Red Maple Wounds Treated with Trichoderma harzianum. K. T. Smith, Former graduate research assistant, Department of Botany and Plant Pathology, University of New Hampshire, Durham 03824; R. O. Blanchard(2), and W. C. Shortle(3). (2)Associate professor of plant pathology, Department of Botany and Plant Pathology, University of New Hampshire, Durham 03824; (3)Research plant pathologist, U.S. Department of Agriculture, Forest Service, Durham NH 03824. Phytopathology 71:496-498. Accepted for publication 30 September 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-496.

Trichoderma harzianum has been used as a biological control agent against wood decay fungi including Fomes connatus, a causal organism of decay in living red maple trees. The growth of T. harzianum and F. connatus in addition to that of Phialophora melinii, an organism that becomes established early in the discoloration and decay process, was compared by using a basal medium containing various concentrations of gallic acid. Trichoderma harzianum and P. melinii were both tolerant of gallic acid, a major phenolic constituent of maple sapwood, but T. harzianum had less capacity to alleviate gallic acid inhibition of F. connatus than did P. melinii. When wounded red maples were treated with T. harzianum in vivo, soluble matter from the green-colored boundaries separating live, healthy sapwood from dead, infected, discolored wood had a greater phenol content than did untreated controls from which P. melinii was commonly isolated. It is known that pioneer fungi such as P. melinii help render wood susceptible to decay by reducing levels of phenols that inhibit decay fungi. Therefore, it is postulated that a mechanism of biological control of decay in red maple trees by T. harzianum is the replacement of pioneer fungi by T. harzianum.