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

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Tatsiana Shymanovich, Postdoctoral Fellow (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Stanley Faeth

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 I). 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 II). 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 III). 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 II). 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 III). 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 IV). 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 had increased overwintering survival than those with E. schardlii or uninfected plants. Artificial inoculations showed that E. alsodes had better compatibility with variety of P. alsodes hosts across latitude than did E. schardlii. Greenhouse plant performance experiment with reciprocally inoculated plants grown under four water-nutrient treatments revealed a complexity of interactions among hosts, endophytes, and environment factors. I found that two isolates of the same endophyte species had ranging effects on plants from one population, indicating genetic variability within endophyte species. Interestingly, neither endophyte increased plant biomass, but some isolates may have other effects such as increased root: shoot ratio, number of tillers, or reduced plant height that may or may not benefit the host plant. Given the lack of clear endophyte effects on host growth by either endophyte species, the differences in distribution may be more related to selection by biotic factors, such as resistance to herbivores and the associated costs and benefits of alkaloid production (Chapter IV). This study has broadened the scientific knowledge on Epichloë distributions and diversity in native grasses and the effects of symbiotic endophytes on host growth and protection from herbivores. This knowledge may have implications for conservation and management of native grasses, many of which are threatened by such factors as overgrazing and climate change. My study may also lead to improved methods for manipulation of endophyte species or strains as natural biocontrol agents in agronomic turf and pasture grasses.

Additional Information

Language: English
Date: 2016
Alkaloid detection, Alkaloid genotypes, Endophyte distribution, Epichloe species, Insect herbivory protection, Interspecific/intraspecific hybrid
Endophytic fungi
Plant-fungus relationships

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