Postulated Mechanism of Biological Control of Decay Fungi in Red Maple Wounds Treated withTrichoderma harzianum

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Abstract
T. 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 and that of Phialophora melinii, an organism that becomes established in the discoloration and decay process, was compared by using a basal medium containing various concentrations gallic acid. T. harzianum and P. melinii were 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. Pioneer fungi such as P. melinii help render wood susceptible to decay by reducing levels of phenols that inhibit decay fungi. A mechanism of biological control of decay in red maple trees by T. harzianum is the replacement of pioneer fungi by T. harzianum.