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Genetic Variability of Canadian Populations of the Sapstain Fungus Ophiostoma piceae

First and fourth authors: Centre de recherche en biologie forestière, Université Laval, Cité universitaire, Québec, Canada G1K 7P4; second author: Forintek Canada Corp., Eastern Laboratory, 319 rue Franquet, Sainte-Foy, Québec G1P 4R4; and third author: Canadian Forest Service, Laurentian Forestry Centre, 1055 rue du PEPS, Sainte-Foy, Québec G1V 4C7

Genetic diversity was studied in seven Canadian populations of Ophiostoma piceae, the most prevalent sapstain fungus in Canadian softwoods. A total of 239 single-spore isolates were recovered following a systematic survey of sapstain fungi in logs and lumber at seven selected sawmills in six Canadian provinces (British Columbia, Alberta, Saskatchewan, Ontario, Québec, and New Brunswick). Sampling was carried out on five commercially important softwood species: balsam fir (Abies balsamea), white spruce (Picea glauca), black spruce (Picea mariana), jack pine (Pinus banksiana), and lodgepole pine (Pinus con-torta var. latifolia). The A and B mating types occurred at equal frequency (MAT A/ MAT B = 1.00:1.13) over all populations. Pseudo-allelic frequencies were estimated at each of 24 putative genetic loci by scoring for presence or absence of random amplified polymorphic DNA fragments generated by five primers. A total of 237 haplotypes were found among the 239 isolates, revealing a high level of genotypic diversity among isolates. Total gene diversity (H_T = 0.414) was mostly attributable to diversity within populations (H_S = 0.369). Thus, only 11.2% of the total variability was attributable to frequency differences among populations. An analysis of molecular variance revealed that most genetic variability occurred within subpopulations within mills (84.3%; P < 0.001), whereas low but statistically significant levels of genetic differentiation were also observed among subpopulations within populations (5.4%; P < 0.001) and among populations (10.3%; P < 0.001). Estimates of Nei' genetic distances were not correlated with geographic distances among sampling locations (r = -0.092; P = 0.310), although principal component analysis indicated that subpopulations located east of Saskatchewan were grouped on the same side of the second principal component axis. Overall, results suggest moderate genetic differentiation of O. piceae in Canada, which is consistent with the observation that sexual reproduction is frequently observed in this fungus.