Little to no genetic structure in the ectomycorrhizal basidiomycete Suillus spraguei (Syn. S. pictus) across parts of the Northeastern USA

Understanding introduction history: Genetic structure and diversity of the edible ectomycorrhizal fungus, Suillus luteus, in Patagonia (Argentina)

Suillus luteus is a common ectomycorrhizal (EM) fungus associated with several Pinus species. It is distributed throughout the Northern Hemisphere and has been introduced into South America and New Zealand. We examined the genetic structure and population biology of S. luteus, which was introduced into Patagonian plantations with Pinus species in Argentina. Overall, 106 samples were collected at 11 geographically separated sites (i.e., Pinus plantations) along a latitudinal gradient in Patagonia (ca. 38°-46° south latitude). Phylogenetic analyses confirmed placement in S. luteus. Genetic analysis demonstrated moderate within-site genetic diversity, but low differentiation between sites. No clear clusters were detected geographically or in relation to host species of Pinus. Our results suggest that the weak genetic structure of the species reflects the short time that has elapsed since the introduction of S. luteus into Patagonia, and its expansion with exotic afforestation there. Moreover, the lack of structure is consistent with a founder effect, suggesting the introduction of a small number of genets that spread throughout all the plantations. Therefore, the high level of gene flow and weak genetic structure observed are probably related to the anthropogenic movement of inoculum associated with forestry practices.

Ectomycorrhizal fungal communities in alpine relict forests of Pinus pumila on Mt. Norikura, Japan

Ectomycorrhizal (ECM) symbioses are indispensable for the establishment of host trees, yet available information of ECM symbiosis in alpine forests is scarce. Pinus pumila is a typical ice age relict tree species in Japan and often forms monodominant dwarf vegetation above the tree line in mountains. We studied ECM fungi colonizing P. pumila on Mt. Norikura, Japan, with reference to host developmental stages, i.e., from current-year seedlings to mature trees. ECM fungal species were identified based on rDNA ITS sequences. Ninety-two ECM fungal species were confirmed from a total of 2480 root tips examined. Species in /suillus-rhizopogon and /wilcoxina were dominant in seedling roots. ECM fungal diversity increased with host development, due to the addition of species-rich fungal lineages (/cenococcum, /cortinarius, and /russula-lactarius) in late-successional stages. Such successional pattern of ECM fungi is similar to those in temperate pine systems, suggesting the predominant role of /suillus-rhizopogon in seedling establishment, even in relict alpine habitats fragmented and isolated for a geological time period. Most of the ECM fungi detected were also recorded in Europe or North America, indicating their potential Holarctic distribution and the possibility of their comigration with P. pumila through land bridges during ice ages. In addition, we found significant effects of soil properties on ECM fungal communities, which explained 34.1% of the total variation of the fungal communities. While alpine vegetation is regarded as vulnerable to the ongoing global warming, ECM fungal communities associated with P. pumila could be altered by the edaphic change induced by the warming.

SSR-based identification of genetic groups within European populations of Tuber aestivum Vittad

Tuber species are ectomycorrhizal ascomycetes establishing relationships with different host trees and forming hypogeous fruiting bodies known as truffles. Among Tuber species, Tuber aestivum Vittad. has a wide distributional range being found naturally all over Europe. Here, we performed large-scale population genetic analyses in T. aestivum to (i) investigate its genetic diversity at the European scale, (ii) characterize its genetic structure and test for the presence of ecotypes and (iii) shed light into its demographic history. To reach these goals, 230 ascocarps from different populations were genotyped using 15 polymorphic simple sequence repeat markers. We identified 181 multilocus genotypes and four genetic groups which did not show a clear geographical separation; although, one of them was present exclusively in Southeast France, Italy and Spain. Fixation index values between pairs of genetic groups were generally high and ranged from 0.29 to 0.45. A significant deficit of heterozygosity indicated a population expansion instead of a recent population bottleneck, suggesting that T. aestivum is not endangered in Europe, not even in Mediterranean regions. Our study based on a large-scale population genetic analysis suggests that genetically distinct populations and likely ecotypes within T. aestivum are present. In turn, this study paves the way to future investigations aimed at addressing the biological and/or ecological factors that have concurred in shaping the population genetic structure of this species. Present results should also have implications for the truffle market since defining genetic markers are now possible at least for some specific T. aestivum genetic groups.