Fungal endophytes of cool-season grasses: Ecological factors determining hyphal loading

Cool-season grasses infected with asexual endophytic fungi are known to have advantages over uninfected grasses, including increased herbivore resistance. Since these fungi reproduce by growing into the developing seeds of the host, hyphal loading (amount of fungal hyphae in the plant) is an important aspect of this symbiosis. The objective of this thesis was to determine the impact of different ecological factors on hyphal loading. In a greenhouse experiment, higher cutting frequencies (simulated herbivory) decreased hyphal loading in F. rubra and L. perenne. Host genotype also influenced hyphal loading. Hyphal loading, estimated using an immunoblot assay, increased significantly during the growing season in F. pratensis in northern Swedish experimental plots; in this species, cutting increased hyphal loading. Fertilization treatments and ley (paddock) age did not have a clear effect on hyphal loading, but high infection rates were found in grazed paddocks and Festuca varieties sampled. These results indicate that simply screening grass plants for endophyte infection status may not be adequate for understanding the ecological significance of fungal endophytes, but that the quantity of endophytic hyphae in infected grasses may also need to be taken into account.