Abstract
Epichloid endophytes are well known symbionts of many cool-season grasses that may alleviate environmental stresses for their hosts. For example, endophytes produce alkaloid compounds that may be toxic to invertebrate or vertebrate herbivores. Achnatherum robustum, commonly called sleepygrass, was aptly named due to the presence of an endophyte that causes toxic effects to livestock and wildlife. Variation in alkaloid production observed in two A. robustum populations located near Weed and Cloudcroft in the Lincoln National Forest, New Mexico, suggests two different endophyte species are present in these populations. Genetic analyses of endophyte-infected samples revealed major differences in the endophyte alkaloid genetic profiles from the two populations, which were supported with chemical analyses. The endophyte present in the Weed population was shown to produce chanoclavine I, paspaline, and terpendoles, so thus resembles the previously described Epichloë funkii. The endophyte present in the Cloudcroft population produces chanoclavineI, ergonovine, lysergic acid amide, and paspaline, and is an undescribed endophyte species. We observed very low survival rates for aphids feeding on plants infected with the Cloudcroft endophyte, while aphid survival was better on endophyte infected plants in the Weed population. This observation led to the hypothesis that the alkaloid ergonovine is responsible for aphid mortality. Direct testing of aphid survival on oat leaves supplemented with ergonovine provided supporting evidence for this hypothesis. The results of this study suggest that alkaloids produced by the Cloudcroft endophyte, specifically ergonovine, have insecticidal properties.
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Acknowledgments
We thank Melissa Robbins for aphid counts; Miranda Weavil and David Zich for technical assistance with alkaloid analysis; The Samuel Roberts Noble Foundation and Bradley Hall, Ginger Swoboda for help with PCR analysis; Li Chen and Dr. Christopher L. Schardl (University of Kentucky) for designing and providing primers to the dmaW EN; Dr. Wade Mace and Kristy Baker at AgResearch, New Zealand for indole-diterpene analyses; Dr. Jonathan Sheerer of the College of William and Mary for synthesizing N-acetylnorloline, Dr. David E. Nichols of Purdue University for synthesis of lysergic acid amide; University of North Carolina at Chapel Hill (Charles Mitchell lab) for supplying the NY aphid strain; Jonathan Newman for constructive comments. Supported by NSF grant DEB 0917741 to SHF and NBC.
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Shymanovich, T., Saari, S., Lovin, M.E. et al. Alkaloid Variation Among Epichloid Endophytes of Sleepygrass (Achnatherum robustum) and Consequences for Resistance to Insect Herbivores. J Chem Ecol 41, 93–104 (2015). https://doi.org/10.1007/s10886-014-0534-x
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DOI: https://doi.org/10.1007/s10886-014-0534-x