Submitted to: Journal of Toxicology Toxins Reviews
Publication Type: Book / Chapter
Publication Acceptance Date: November 18, 2008
Publication Date: August 7, 2009
Citation: Belesky, D.P., Bacon, C.W. 2009. TALL FESCUE AND ASSOCIATED MUTUALISTIC TOXIC FUNGAL ENDOPHYTES IN AGROECOSYSTEMS. Journal of Toxicology Toxins Reviews. 28(2-3):102-117. Technical Abstract: Bacon et al. (1977) proposed and Hoveland et al. (1980, 1986) substantiated that impaired health and performance of livestock grazing tall fescue [Lolium arundinaceum S. J. Darbyshire, formerly Festuca arundinacea Schreb.] were associated with the fungal endophyte Neotyphodium coenophialum Glenn, Hanlin and Bacon. This endophyte was initially identified as anamorphic state of the teleomorph Epichloe typhina (Pers.) Tul., Spcaelia typhinum, and later called Acremonium coenophialum, Morgan-Jones et Gams (Morgan-Jones and Gams, 1982). However, detailed studies utilizing molecular genetics returned it to the family Clavicipitales as N. coenophialum Glenn, Hanlin, and Bacon (Glenn et al., 1996). This fungus dwells within the intercellular spaces of stems and leaf sheaths of all native tall fescue. Thus, livestock producers do not have many choices for non-infected tall fescue. Indeed there are no cool-season perennial forages that would tolerate the punishing weather, inhospitable soil, and performance demands of beef operations in the southeastern portion of the USA. Consequently, tall fescue is grown on about 14 million hectares in the USA. Hot, dry summers; acidic, clayey soils; and occasional heavy application rates of poultry manure occurring along with the defoliation and physical damage associated with grazing, placed numerous environmental and management-induced stresses on the plant. Both the incidence and widespread infection with the endophyte account for the highly toxic consequences on animal production systems. While current estimation is not available, an economic estimate based on animals reared on tall fescue suggests that the impact on beef cow-calf production exceeds 750 million dollars annually (Stuedemann and Hoveland, 1988). In addition to beef cattle, dairy cattle are also impacted but estimates on losses are not available. Sheep, and horses, especially mares, are also affected. We present a historic review of the work conducted by ARS scientists and their collaborators, which served as benchmarks in current understanding of this remarkable but toxic association. We also include the current impact of these historic studies on management strategies and salient aspects of ecophysiology of endophyte-infected grasses that are driving new discoveries of this association beyond the scope of the toxicity expressed in tall fescue-endophyte associations.