Analysis of genet size and local gene flow in the ectomycorrhizal basidiomycete Suillus spraguei (synonym S. pictus)

Abstract

Several recent fine-scale genetic structure studies of ectomycorrhizal fungi have reported significant spatial clustering of genets with similar genotypes, supporting locally restricted gene flow. In this study we used genotype data from microsatellite markers and spatial autocorrelation analysis to examine local gene flow in Suillus spraguei at distances up to 2 km. Previously developed microsatellite markers for S. spraguei from Japan were unsuccessful at amplifying DNA isolated from sporocarps found in New York state, and other research suggested that both are disjunct species. Novel microsatellite markers therefore were developed with New York specimens. We identified nine polymorphic microsatellite loci and developed primer sets to amplify these regions. We tested the efficiency of the primer sets on 50 sporocarps collected from a natural Pinus strobus stand. The majority of the markers were in Hardy-Weinberg and linkage equilibrium. The location of all sampled sporocarps was recorded and used along with multilocus genotype data to create a genet map. The distance between sporocarps with the same multilocus genotype was small (≤ 7.65 m) and the majority of sporocarps collected were genetically unique, suggesting frequent spore establishment and sexual recombination on this site. Spatial autocorrelation analysis did not support clustering of similar genotypes, suggesting few restrictions to gene flow within this local population.

• ectomycorrhizal fungi
• microsatellite
• simple sequence repeat
• spatial autocorrelation

We thank Michael O’Brien and Ning Sun for aid creating the genet maps and Joseph Vineis, Tera Galante and Drs Thomas Horton, Lawrence Smart and William Powell for advice and support. Financial support for this research was provided by a USDA-CSREES McIntire-Stennis grant (to Annette Kretzer). Generation of microsatellite-enriched libraries from Suillus spraguei was a project of the Molecular Biology Techniques course (BTC401/EFB601) in fall 2006 and spring 2008, and the authors thank all students for their contributions and good spirits.