Tall fescue and associated mutualistic toxic fungal endophytes in agroecosystems

Abstract

For the past 35 years, a significant effort was devoted to identifying the cause of tall fescue toxicosis, a symptomless infection of tall fescue (Schedonorus phoenix [Scop.] Holub, formerly Lolium arundinaceum [Schreb.] S. J. Darbyshire, and formerly Festuca arundinacea Schreb.) by a fungal endophyte Neotyphodium coenophialum Glenn, Hanlin, and Bacon. This endophyte grows intercellularly in stems and leaf sheaths of the host plant. Among the cool-season perennial forages, only tall fescue tolerated the punishing weather, inhospitable soil, and performance demands of beef operations on a consistent basis in the southeastern portion of the United States. Consequently, tall fescue became the forage grass of choice, which led eventually to its production on about 14 million hectares nationwide. Weather and soil conditions place numerous environmental- and management-induced stresses on the plant–fungus association that influence plant persistence and nutritive value, including alkaloid production. Livestock performance on endophyte-free tall fescue was shown to be superior to that obtained on endophyte-infected tall fescue, establishing the role of fungus in the syndrome. The suite of symptoms presenting in grazing cattle resembled ergotism but much of the early research did not target mycotoxins related to this malady. After discovery of the endophyte inhabiting tall fescue, research documented production of several types of ergot and other classes of alkaloids. This led, eventually, to numerous experiments designed to develop management strategies that reduced the toxic effects of host–endophyte associations on livestock health. Accumulation patterns of biologically active alkaloids and their responses to management were defined, suggesting possible ecological value of host–endophyte associations, and ultimately led to genetic approaches that minimized production of mycotoxins, while maintaining persistence and other agronomic traits of this valuable forage grass.

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Acknowledgments

We recognize and value contributions made by others too numerous to mention, including students, technicians, farmers, clerical staff, and research colleagues whose names were not mentioned in this review. Their intellectual input, diligence, and dedicated efforts helped make the successes of the many collaborative research programs on host–endophyte–livestock interactions reality.

Declaration of interest: The authors report no conflicts of interest.