COS 5-5
Foliar fungi in Populus: Community assembly and pathogen resistance
Historical contingencies in community assembly and the disproportionate influence of early-arriving species (priority effects) have been shown to shape community composition in a variety of systems. In this study, we sought to understand the magnitude and consequences of these effects on communities of foliar fungi in Narrowleaf Cottonwood, Populus angustifolia. To do so, we grew clonal cuttings of Populus in a greenhouse and inoculated the leaves of each plant with one of eight different species of fungal endophyte (fungi that grow asymptomatically within leaves) or a sterile water control. After inoculation, we returned cuttings to the common garden (in Ogden, UT) from which they were originally collected. Over the course of six weeks in the field, the plants were exposed to natural propagules (i.e. spores, conidia), from other endophytes as well as pathogens. We also deployed spore traps in the same location to assay the set of species producing these environmental propagules. At the end of this period, we collected leaves from each plant and quantified premature senescence and leaf necrosis. We then used 454 pyrosequencing of the ITS1 region to assay both the leaf-associated fungal communities and the propagules collected in spore traps.
Results/Conclusions
Inoculation with endophytes has been shown to be an effective means to reduce the damage caused by foliar pathogens. However, we still have little understanding of how or why these protective effects occur. This is especially the case when considering the complex and species-rich communities of foliar microorganisms that colonize leaves in natural systems. We found in this study that inoculation with endophytic fungi resulted in significantly reduced levels of premature leaf senescence and leaf necrotic area after six weeks of exposure to field conditions, adding support to the idea that endophytes can be effective agents for pathogen control. We also found that fungal species richness (number of 95% ITS1 OTUs) was significantly lower in leaves than in the set of environmental propagules collected in the same site. Further, the final makeup of foliar communities was similar across treatments, especially when compared to large differences between the communities captured by spore traps. Together, these results contribute to a growing understanding of the role of endophytes in plant-pathogen interactions, and the ways in which community assembly processes may influence these interactions.