Development of Discoloration, Decay, and Microorganisms Following Wounding of Sweetgum and Yellow-Poplar Trees

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Abstract
Patterns of development of discoloration, decay and microorganisms were studied in 122 naturally or experimentally wounded sweetgum (Liquidambar styraciflua) and yellow-poplar (Liriodendron tulipifera) trees. Heartwood and wound-initiated discolorations were found in yellow-poplar, but sweetgum contained only wound-initiated discoloration. Barrier zones of abnormal cells were found in both species and appeared to account, at least in part, for compartmentalization of the stem. Xylem formed after wounding was free of discoloration and decay, and of the large populations of microorganisms that developed in wood formed prior to wounding. Sparse populations of bacteria (200-4000 cells/g wood) and small-spored fungi (5-150 propagules/g wood) were detected by dilution plating of homogenates of normal sapwood from wounded and nonwounded trees. Some genera of the fungi found in normal sapwood (Phialophora, Fusarium, Cephalosporium and Streptomyces) colonized discolored sapwood. Abundant populations of bacteria (> 105 cells/g) and these same fungi (up to 103 propagules/g) were found in discolored wood from which most bits of tissue plated in agar media also yielded microorganisms. The tissue plating method seldom yielded bacteria when populations were < 103 cells/g, but bacteria were isolated routinely when populations were > 103 cells/g. Some of the bacteria and fungi that colonize discolored wood exist as sparse populations in normal sapwood.