Microbiome Diversity of Endophytic Fungi across Latitudinal Gradients in West Coast Douglas-Fir (Pseudotsuga menziesii) Foliage

Research on forest microbiota lags far behind that of agricultural crops. Understanding of host-pathogen complications is exemplified in defoliation of Douglas-fir dominated forests. Although linked to Phaeocryptopus gaeumannii, etiology of the disease contrasts dramatically with previously known effects. Climate variables and seed source have been suggested as causal, however the number of potential endophytes makes the segregation of a single pathogen for needle cast problematic. A randomized block design was used to assess endophyte populations between seed sources along a latitudinal gradient among a reciprocal provenance study of Douglasfir. Needles were surface sterilized and underwent plate culturing. Isolated fungal colonies were identified through Sanger sequencing and analyzed through BLAST. Differences in seed source and environmental gradient were analyzed by log odds ratio while community relationships were identified through two-way cluster analyses. Linear mixed models were used to evaluate random error associated with seed source data. Forty-six unique isolates from 39 taxa were identified. Infection rates for all needles was 39%, ranging from 5% to 60% among seed sources. Infection rates were higher for non-source needles on three sites. Community structure analyses showed relationships between sample units and endophyte species and strong evidence exists for the influence of seed source type on the relationship between continentality variables and mean average number of endophytes. Ordination demonstrates some evidence for differences between endophyte communities among sites, overcoming any influence provided by seed source type. This study expands the previous known list of Douglas-fir endophytes and outlines fungal community structures based on environmental variables and seed source provenance. This study demonstrated that fungal biodiversity is highly variable in Douglas-fir foliage, and may be influenced by environmental variables, including the provenance of the seed source or the climate at the growing site. Interest in microbiome communities will inevitably lead to advances in management practices.