Graduate Thesis Or Dissertation
 

Fungal colonization of Douglas-fir sapwood

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  • The fungi that cause mold and stain of freshly sawn lumber result in millions of dollars in losses to the forest products industry. Stain and mold are typically prevented by either kiln drying or by application of a topical fungicide. While these treatments are effective, kiln drying is costly and many mills object to use of chemicals. One alternative to conventional stain prevention is biological control. One problem with this approach on western wood species such as Douglas-fir is the lack of information on the target stain and mold fungi that colonize the sapwood of this species. The fungi colonizing freshly sawn Douglas-fir sapwood were isolated and identified by culturing lumber obtained from 4 different locations in the Willamette Valley in western Oregon using regular, streptomycin amended or streptomycin/cycloheximide amended malt extract agar. The ability of each taxa to cause discoloration was evaluated in a laboratory discoloration test. A total of 547 fungi were isolated from Douglas-fir sapwood, representing 24 genera and 45 species. Graphium species were the most frequently isolated fungi, representing 17.4 percent of all isolates. Most of these isolates were considered as anamorphs of Ophiostoma piceae. Other frequently isolated sapstaining fungi included Cephaloascus fragrans, Aureobasidium pullulans, Rhinocladiella cellaris, Cladosporium cladosporioides and Scytalidium lignicola. Molds, primary Penicillium and Trichoderma species, were frequently isolated, and may represent potential biological control organisms or competitors of biological control organisms because of their antagonistic characteristics. Many fungal species of unknown biological significance were also isolated from Douglas-fir sapwood, and their roles in the stain development merit further study. Media and lumber source both affected the fiingal flora isolated. Among stain fungi, Graphium species exclusively occurred on cycloheximide amended media. There was also close relationship between the degree of fungal colonization and the length of time after the lumber was cut. The degree of discoloration exceeded 70 percent in all Graphium species. Cephaloascus fragrans, Aureobasidium pullulans, Rhinocladiella cellaris, Cladosporium cladosporioides, Scytalidium lignicola and Thysanophora penicillioides also produced extensive staining of Douglas-fir sapwood. Mold isolates also caused discoloration of Douglas-fir sapwood wafers, although their discoloration could be easily removed. All Penicillium species produced over 90 percent discoloration, while Trichoderma species produced 80 to 86 percent discoloration. The results indicate that Graphium species are the primary stain fungi on Douglas-fir sapwood, however, other species were also capable of colonizing this material.
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