Environmental factors affect the distribution of two Epichloë fungal endophyte species inhabiting a common host grove bluegrass (Poa alsodes).

Tatsiana Shymanovich,Stanley H. Faeth

doi:10.1002/ece3.5241

Tatsiana Shymanovich, Stanley H. Faeth

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https://doi.org/10.1002/ece3.5241

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Abstract

AimThe endophyte Epichloë alsodes, with known insecticidal properties, is found in a majority of Poa alsodes populations across a latitudinal gradient from North Carolina to New York. A second endophyte, E. schardlii var. pennsylvanica, with known insect‐deterring effects, is limited to a few populations in Pennsylvania. We explored whether such disparate differences in distributions could be explained by selection from biotic and abiotic environmental factors.LocationAlong the Appalachian Mountains from North Carolina to New York, USA.TaxonFungi.MethodsStudied correlations of infection frequencies with abiotic and biotic environmental factors. Checked endophyte vertical transmission rates and effects on overwintering survival. With artificial inoculations for two host populations with two isolates per endophyte species, tested endophyte–host compatibility. Studied effects of isolates on host performances in greenhouse experiment with four water‐nutrients treatments.ResultsCorrelation analysis revealed positive associations of E. alsodes frequency with July Max temperatures, July precipitation, and soil nitrogen and phosphorous and negative associations with insect damage and soil magnesium and potassium. Plants infected with E. alsodes had increased overwintering survival compared to plants infected with E. schardlii or uninfected (E−) plants. Artificial inoculations indicated that E. alsodes had better compatibility with a variety of host genotypes than did E. schardlii. The experiment with reciprocally inoculated plants grown under different treatments revealed a complexity of interactions among hosts, endophyte species, isolate within species, host plant origin, and environmental factors. Neither of the endophyte species increased plant biomass, but some of the isolates within each species had other effects on plant growth such as increased root:shoot ratio, number of tillers, and changes in plant height that might affect host fitness.Main conclusionIn the absence of clear and consistent effects of the endophytes on host growth, the differences in endophyte‐mediated protection against herbivores may be the key factor determining distribution differences of the two endophyte species.

Highlights

Plant microbial symbionts, such as various groups of fungi and bac‐ teria, play an important role in plant stress resistance against various abiotic and biotic selective pressures (Johnson, Graham, & Smith, 1997; Rodriguez, White, Arnold, & Redman, 2009; Rosenblueth & Martínez‐Romero, 2006; Schulz, 2006)
Our study showed that the frequencies of the two endophyte species, E. alsodes and E. schardlii var. pennsylvanica, were cor‐ related with key environmental factors
Our study explored several explanations for the broader distribu‐ tion range and higher frequency of the interspecific hybrid, E. al‐ sodes, compared to the limited distribution of intraspecific hybrid species, E. schardlii var. pennsylvanica

Summary

Introduction

Plant microbial symbionts, such as various groups of fungi and bac‐ teria, play an important role in plant stress resistance against various abiotic and biotic selective pressures (Johnson, Graham, & Smith, 1997; Rodriguez, White, Arnold, & Redman, 2009; Rosenblueth & Martínez‐Romero, 2006; Schulz, 2006). One group of plant symbionts, Epichloë species, systemic endo‐ phytic fungi of cool season grasses, has been shown to mitigate the effects of environmental stress such as drought and nutrient defi‐ ciencies as well as anthropomorphic stresses such as elevated CO2 associated with climate change and resisting invasive species (Brosi et al, 2011; Compant, Heijden, & Sessitsch, 2010; Craig et al, 2011; Malinowski & Belesky, 2000) These fungi may produce alkaloid compounds that have toxic or deterrent effects on various herbivores, reducing environmental stress from insect herbiv‐ ory and vertebrate grazing (Brosi et al, 2011; Cheplick & Faeth, 2009; Compant et al, 2010; Craig et al, 2011; Hunt, Rasmussen, Newton, Parsons, & Newman, 2005; Malinowski & Belesky, 2000; Schardl, Balestrini, Florea, Zhang, & Scott, 2009). Epichloë endophytes that are thought to be strictly vertically (maternally) transmitted are considered more strongly mutualistic because host plant and endo‐ phyte reproduction, and fitness, are closely linked (Cheplick & Faeth, 2009; Clay & Schardl, 2002)

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