DIVERSITY OF FUNGI CAUSING SAPSTAIN IN CANADIAN SOFTWOODS
L BERNIER1, P GAGNÉ1, DQ YANG2, M GIGNAC2, A BYRNE3, A UZUNOVIC4, SH KIM 4 and C BREUIL4
1Centre de recherche en biologie forestière, Université Laval, Québec, Qc, Canada, G1K 7P4; 2Forintek Canada Corp., Eastern Laboratory, Sainte-Foy, Qc, Canada, G1P 4R4; 3Forintek Canada Corp., Western Laboratory, Vancouver, BC, Canada, V6T 1W5; 4Department of Wood Science, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
Background and objectives
Sapstain, a cosmetic wood discoloration caused by fungi, results in significant financial losses for lumber producers. Little is known, however, about the identity, biology and ecology of the micro-organisms involved in stain. Thus, a systematic survey of staining fungi found in logs and lumber was conducted at selected sawmills across Canada. The objectives of this survey were (i) to identify the fungi involved in discolouration of commercially important softwoods; and (ii) to evaluate the genetic diversity among isolates of the fungal species found to be predominant in Canada.
Materials and methods
Sampling was conducted in the summer of 1997 in seven sawmills located in six provinces from the western (British Columbia, Alberta and Saskatchewan) and eastern (Ontario, Québec and New Brunswick) parts of Canada. Five softwood species were selected: lodgepole pine (Pinus contorta), jack pine (P. banksiana), balsam fir (Abies balsamea), black spruce (Picea mariana) and white spruce (P. glauca). In each mill, sawn timber and fresh logs were set aside and sampled after one month. Fungi isolated from stained wood were identified on the basis of their morphological features, growth rate, and, where appropriate, mating reactions with known tester strains. Genomic DNA was extracted from selected isolates and amplified with both specific- and RAPD primers.
Results and conclusions
At most sites the experimental timber showed substantial stain development. Ophiostomatoid fungi, which customarily include genera Ophiostoma and Ceratocystis, were the most common organisms associated with sapstain. Ophiostoma piceae was frequently isolated from sawn timber in all mills. It was also frequently isolated from logs in eastern Canada, but less frequently in western Canada. Other Ophiostomatoid species included O. piliferum, O. minus, O. flexuosum, O. piceaperdum, O. ips, C. adiposa, C. coerulescens and different species of Leptographium. At least two other groups of fungi morphologically similar to O. piceae were also recovered but failed to mate with O. piceae, indicating that they are separate taxa. Other fungi isolated from stained wood included the black yeast Aureobasidium pullulans, Phacidium coniferarum, and molds belonging to the genera Penicillium, Aspergillus, Alternaria, Mucor, Cladosporium and Trichoderma. Preliminary assessment of genetic diversity in O. piceae suggests that the two mating-type alleles occur at equal frequency. RAPD analysis also showed the occurrence of extensive genetic diversity within this species.