Signatures of Post-Glacial Genetic Isolation and Human-Driven Migration in the Dothistroma Needle Blight Pathogen in Western Canada

Abstract

Many current tree improvement programs are incorporating assisted gene flow strategies to match reforestation efforts with future climates. This is the case for the lodgepole pine (Pinus contorta var. latifolia), the most extensively planted tree in western Canada. Knowledge of the structure and origin of pathogen populations associated with this tree would help improve the breeding effort. Recent outbreaks of the Dothistroma needle blight (DNB) pathogen Dothistroma septosporum on lodgepole pine in British Columbia and its discovery in Alberta plantations raised questions about the diversity and population structure of this pathogen in western Canada. Using genotyping-by-sequencing (GBS) on 119 D. septosporum isolates from 16 natural pine populations and plantations from this area, we identified four genetic lineages, all distinct from the other DNB lineages from outside of North America. Modeling of the population history indicated that these lineages diverged between 31.4 and 7.2k years ago, coinciding with the last glacial maximum and the post-glacial recolonization of lodgepole pine in western North America. The lineage found in the Kispiox Valley from British Columbia, where an unprecedented DNB epidemic occurred in the 1990s, was close to demographic equilibrium and displayed a high level of haplotypic diversity. Two lineages found in Alberta and Prince George (British Columbia) showed departure from random mating and contemporary gene flow, likely resulting from pine breeding activities and material exchanges in these areas. The increased movement of planting material could have some major consequences by facilitating secondary contact between genetically isolated DNB lineages, possibly resulting in new epidemics.

Worldwide Genetic Structure Elucidates the Eurasian Origin and Invasion Pathways of Dothistroma septosporum, Causal Agent of Dothistroma Needle Blight

“…Individual population studies have shown unexpected levels of diversity in many populations [20][21][22][23][24][25][26][27][28][29]. This diversity indicates that sexual reproduction is more common than previously thought, particularly as the sexual stage (previously known as Mycosphaerella pini) has only rarely been observed, and the asexual stage is ubiquitous.…”

Rapid Detection of Pine Pathogens Lecanosticta acicola, Dothistroma pini and D. septosporum on Needles by Probe-Based LAMP Assays

“…However, many other biotic, abiotic and anthropogenic factors could be important drivers for needle blights epidemics. Among these, the movement of infected planting material between regions and countries is thought to be the main anthropogenic pathway of L. acicola, D. pini and D. septosporum [28][29][30][31].…”

Development of a Rapid Loop-Mediated Isothermal Amplification Assay for the Detection of Dothistroma septosporum

“…The results of this study further confirm the suitability of this locus as a diagnostic for D. septosporum. The sample population of D. septosporum assembled for this study was geographically diverse, with samples representing the different geographic subgroups identified by Capron et al [4], as well as samples from Alaska, California, Oregon, and New Zealand, suggesting that the assay has wide applicability.…”

“…As historical distribution records in Canada are based on morphology, it will be necessary to use DNA-based methods to fully understand the geographic distribution of these pathogens. Development of a LAMP diagnostic assay for D. septosporum was prompted by the finding that this species was causing Dothistroma needle blight in Alberta [3,4].…”

“…latifolia Engelm., Pinus banksiana Lamb., and their hybrid, in northern Alberta, Canada [3]. The identification of D. septosporum in Alberta and the potential for eastward spread through the boreal forest have led to research into population genomics [4], host range [3], and, as we describe here, rapid diagnostics for D. septosporum, the pathogen associated with the disease in western Canada.…”