The effects of endophytic Epichloe species on host plant fitness of two native grasses, Poa alsodes and Achnatherum robustum

Most plants harbor microbial symbionts, which often affect host performance and fitness. Endophytic Epichloe species are systemic fungal microbial symbionts of many cool-season pooid grasses. Benefits to the host from Epichloe infection include increased resistance to stressful environmental factors, such as drought and limited soil nutrients, due to morphological and physiological changes. The major benefit of Epichloe infection is enhanced protection against herbivory due to production of fungal alkaloids. The fungal alkaloids have varying activity against invertebrate or mammalian grazers. Although Epichloe endophytes are well-studied in agronomic grasses such as tall fescue and perennial ryegrass, little is known about the how the presence of different endophyte species and their frequencies and distribution are related to environmental factors in native grasses. Using two native grasses to eastern [Poa alsodes (Grove Bluegrass)] and western [Achnatherum robustum (Sleepygrass)] North America, I addressed the following questions: 1) how are endophyte species distributed among populations along a latitudinal gradient, 2) what fungal alkaloids are produced by different endophyte species, 3) how do fungal alkaloids affect insect herbivores, and 4) what are the effects of different endophytes on host plant growth? (Abstract shortened by ProQuest.).