Exploring fungal endophyte diversity in invasive Phragmites australis
The invasive subspecies of the common reed, Phragmites australis var. australis, is a particularly invasive organism that occurs widely throughout temperate wetlands and waterways throughout the United States. As with nearly all plants studied, Phragmites serves as a host to endophytic fungi that asymptomatically colonize its various tissues and organs. Manipulation of the endophyte flora represents a potential direction for controlling invasive Phragmites. The goals of this study were to isolate and characterize fungal endophytes of Phragmites as a function of site and tissue type over one growing season. Individual tillers were collected from nine different sites along the Great Lakes in Indiana and Michigan in 2013. A total of 1,008 tissue samples from leaves, stems, rhizomes, inflorescences, and seeds from 164 tillers were surface sterilized and plated on cornmeal agar supplemented with tetracycline to inhibit bacterial growth. In total, 884 fungal isolates were obtained and were first grouped into morphospecies using macroscopic and microscopic phenotypic characteristics. These morphospecies were identified using Sanger sequencing of the ITS1, 5.8S ribosomal subunit, and ITS2 regions.
In total, 65 operational taxonomic units (OTUs) were identified, belonging to 41 genera and 18 orders. OTUs belonging to the orders Hypocreales and Pleosporales comprised the majority of samples (45% and 34% respectively) and the five most common taxa isolated were Acremonium strictum (32.7%), Alternaria alternata (13.7%), Fusarium sporotrichoides (7.3%), Phoma sp. (7.0%), and Phaeosphaeria phragmitis (2.9%). There was variation in tissue specificity among OTUs as well as variation among sites. For example, A. alternata was found almost exclusively in leaf tissue and Phialocephala sp. was found only in rhizome tissue. Similarly, F. sporotrichoides was isolated primarily from samples collected in western Michigan while Phoma sp. was isolated primarily from the Indiana Dunes samples. Comparison of results with previous literature found that Phragmites in the Great Lakes region harbor distinct endophytic communities when compared to European populations. Future research should focus on the biological significance of these endophytes to determine their role in Phragmites invasiveness.