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Interaction of Live Sapwood and Fungi Commonly Found in Discolored and Decayed Wood. Walter C. Shortle, Research Assistant, Departments of Plant Pathology and Forestry, North Carolina State University, Raleigh, NC 27607, Senior author now: Research Plant Pathologist, Northeastern Forest Experiment Station, Box 640, Durham, NH 03824; Ellis B. Cowling, professor, Departments of Plant Pathology and Forestry, North Carolina State University, Raleigh, NC 27607. Phytopathology 68:617-623. Accepted for publication 4 October 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-617.

Interactions between fungi found in discolored and decayed wood of living sweetgum and yellow-poplar trees and living sapwood were studied in vitro. The results indicated that early colonizers (Ceratocystis coerulescens, Fusarium oxysporum, and F. moniliforme) of discolored wood found within 30 days of wounding: (i) usually grow on live sapwood without inducing wood discoloration, (ii) grow at concentrations of gallic acid inhibitory to decay fungi, (iii) do not persist on dead wood, and (iv) initially outcompete other fungi that colonize wood, but are readily replaced by decay fungi on dead wood. More persistent colonizers (Phialophora bubakii and P. melinii) of discolored wood: (i) neither grow on live sapwood nor induce its discoloration, (ii) grow at levels of gallic acid inhibitory to decay fungi, (iii) persist in wood by utilizing some cell wall substances, and (iv) cannot compete with either early colonizers or decay fungi on living or dead sapwood. Decay fungi (such as Pleurotus ostreatus) which commonly are found on living trees: (i) grow on live sapwood only if they induce discoloration and grow well only after dark pigments have been removed, (ii) are inhibited by levels of gallic acid that have no effect on the growth of the former two groups of fungi, and (iii) replace early colonizers in dead wood. It was concluded that some decay fungi may cause wood discoloration following wounding independent of pioneer fungi and induce a host response which suppresses their growth and temporarily allows pioneer fungi and bacteria to flourish. This view is contrary to the current concept of succession of microorganisms leading to decay in living trees.