Ectomycorrhizal fungi associated with Quercus trees

Seven species of Quercus have been introduced into China from the United States for their ecological and economic values. The identities of ectomycorrhizal (ECM) fungi associated with oak tree roots in new environments, however, are poorly known. In this work, we used traditional and high-throughput approaches to investigate the formation of ECM symbiosis and corresponding fungal partners in nursery seedlings. Our data confirmed that all Quercus species exhibited well-developed ECM roots, evidenced by the formation of Hartig net and mantle structures. The observed ECM types of fungi, however, were not distinctive enough in morphology and color, suggesting that Quercus-associated ECM fungi in nursery seedlings may be less diverse. A combination of isolation and pyrosequencing of fungi from root tips revealed that the mycorrhizal fungal groups represented five orders and twelves genera in the Basidiomycota. Unexpectedly, only Scleroderma (Boletales) was found in both approaches and was the dominant genus. It was further shown that Scleroderma exhibited a lowest degree of host specificity. Particularly, isolates fallen into the Sistotrema displayed taxonomic novelty due to their low internal transcribed spacer sequence similarities (< 90%) compared with known species. Conclusively, our work provides more insights into the identities of fungi associated with Quercus and further symbiosis-based seedling nursing technology.