Diversity and spatial distribution of fungal endophytes in a Eucalyptus grandis tree

[摘要] Endophytic fungi of most woody trees are poorly studied due to their cryptic existence, thecomplexity of the community and the poor ability of traditional tools to characterize them.This study characterised the endophytic community present in commercially importantEucalyptus grandis trees in South Africa. Two different experimental approaches were used.Firstly environmental bar-coding, or metagenetics, was done using 454-pyrosequencingparallel sequencing of the barcode amplicons of all the fungal isolates present in the plantsfrom the total DNA of the plant. Secondly, conventional DNA bar-coding of was done offungal endophyte isolates. Isolates of the Botryosphaeriaceae family of latent endophyticpathogens were further characterised using a multi-gene phylogenetic approach from bothE. grandis and related native S. cordatum that grew in close proximity.The endophytes within the three E. grandis trees were hyper diverse. A total of 1 281Molecular Operational Taxonomic Units (MOTU) was identified based on 454-pyrosequencing of the E. grandis fungal endophyte infections. Only 85 fungal endophyticspecies were identified amongst isolates from one of these trees, using the conventionalDNA bar-coding approach. Fifteen times more species/MOTU was thus recovered using ametagenetics compared to an isolation approach. Despite this high diversity the speciesaccumulation curves indicate that more endophytic diversity is to be discovered. The multigeneanalysis of Botryosphaeriaceae isolates obtained from the E. grandis and S. cordatumtrees show that three species co-infect both these hosts. Two novel host associations arealso reported. This approach of verifying identities of cryptic species with appropriate multigeneanalyses is most likely needed for other diverse species complexes associated withthese trees.A very thorough sampling strategy is required to adequately characterize the endophytediversity in trees. The experimental approach, the 454-pyrosequening identification workflowand database described in this study will be useful to study these endophyte communitiesover time and space in future. Using these techniques and workflows described, questionsrelated to host association, diversity and spatial distribution within hosts, and geographicaldelimitation of endophytes can be addressed.

[发布机构] University of Pretoria