The Effects of Endophytic Epichloë Species on Host Plant Fitness of Two Native Grasses, Poa alsodes and Achnatherum robustum

Shymanovich, Tatsiana

ABSTRACT: Most plants harbor microbial symbionts, which often affect host performance and fitness. Endophytic Epichloë species are systemic fungal microbial symbionts of many cool-season pooid grasses. Benefits to the host from Epichloë 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 Epichloë 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? For each grass species, variation in endophyte species and their alkaloid genetic profiles were determined. Chemical analyses tested alkaloid production that was predicted by molecular genetic profiles. In A. robustum, two distinct endophytes were found in the two populations located near Weed and Cloudcroft in the Lincoln National Forest, New Mexico. One of these is a new, undescribed Epichloë species. Endophytes in A. robustum provided different levels of protection from aphids, and this difference was attributed to presence of the ergot alkaloid, ergonovine produced by endophyte from the Cloudcroft population (Chapter II). I discovered and described a new Epichloë species inhabiting P. alsodes that was widespread at high infection frequencies in populations from North Carolina to New York. Based on phylogenetic analysis of partial tefA and calM genes, this species is an interspecific hybrid of E. amarillans x E. typhina. This new species was described and named E. alsodes based on its host name (Chapter III). E. alsodes does not have functional peramine and ergot alkaloid genes. This endophyte produces only N-acetylnorloline (NANL) alkaloid at high concentrations, which was most likely responsible for complete larval mortality of fall armyworm (Spodoptera frugiperda) larvae in my experimental tests. However, larvae were unable to differentiate toxic plants in choice tests (Chapter IV). Another P. alsodes endophyte, E. schardlli, which is an intraspecific hybrid of two E. typhina strains, was limited in distribution in comparison to E. alsodes and found only in populations in Pennsylvania (Chapter III). Infection by this endophyte had weak effects on larval survival but caused delayed development and reduced pupal weight of S. frugiperda. Moreover, E. schardlii possesses insect-deterring properties, but the compound(s) responsible for this is unclear because peramine, predicted by genotyping, was not detected in leaves by chemical analyses. Both Epichloë species may provide increased protection from insect herbivores but in a different ways (Chapter IV). To explain the differences in the distributions and frequencies of the two endophytes in Poa alsodes populations, I correlated frequencies with abiotic and biotic environmental factors and conducted experimental tests of host performance under controlled environmental conditions (Chapter V). Correlation analysis revealed positive associations of E. alsodes frequency with July maximum (MAX) temperatures, July precipitation, soil nitrogen and phosphorous and negative associations with insect damage and soil magnesium and potassium. Plants with E. alsodes