Black stain root disease (BSRD) is a vascular wilt that causes mortality in several conifer species (Wagener & Mielke 1961, Harrington & Cobb 1987). It is caused by the fungus Leptographium wageneri, which can spread via root contact and is also vectored by insects (Witcosky & Hansen 1985, Witcosky et al. 1986). Douglas-fir (Pseudotsuga menziesii) is host to a specific variety of the fungus, L. wageneri var. pseudotsugae (Harrington & Cobb 1987). The fungus is vectored by two species of weevil (Pissodes fasciatus, Steremnius carinatus) and the Douglas-fir root beetle (Hylastes nigrinus) (Witcosky & Hansen 1985, Witcosky et al. 1986). The incidence and severity of BSRD in young Douglas-fir plantations in the Pacific Northwest has intensified in recent years. This disease is emerging as a serious threat to the health and productivity of young trees in managed forest stands in Oregon. The population structure of the BSRD fungus as it relates to epidemiology has not been investigated previously. It is not currently known whether local or longdistance dispersal is more important for the establishment of new BSRD infections, and the relative genetic diversity of L. wageneri var. pseudotsugae within and between stands has not been described. This study was designed to address these gaps in knowledge and may provide insights into the emergence and spread of BSRD. The specific objectives were to: 1) sequence genomes of L. wageneri var. pseudotsugae isolates collected in western Oregon Douglas-fir plantations; 2) identify single nucleotide polymorphisms (SNP) to assign genotypes; and 3) compare population structure and diversity among plantations, and among stands within plantations, to make inferences about epidemiological characteristics such as dispersal and colonization.
Bennett, Patrick I.; LeBoldus, Jared M. 2020. Insights into the epidemiology and dispersal capabilities of Leptographium wageneri var. pseudotsugae within and between young Douglas-fir stands in western Oregon. In: Reynolds, G. J.; Wilhelmi, N. P.; Palacios, P., comps. Proceedings of the 66th Western International Forest Disease Work Conference, Estes Park, Colorado, 3-7 June 2019. p. 117-123.