Ergot Toxicity from Endophyte‐Infected Grasses: A Review1

Abstract

AbstractClarifying the role of grasses parasitized by a tribe of clavicipitaceous endophytes (Balansiae) in the etiology of the many cattle (Bos taurus) ergot toxicity syndromes is essential for identifying the correct toxic grass and establishing the proper pasture management practice necessary to eliminate toxicity. The distinction is required as the management practice used to prevent ergot toxicity by Clavicepsdoes not apply because of the systemic habit of the Balansiae. Research is reviewed, which established that endophytic parasites of many genera of warm‐season perennial weed grasses and tall fescue (Festuca arundinaceaSchreb.) are producers of toxic ergot alkaloids. This group of fungi is distinct from the closely related genus Clavicepsin being an intercellular parasite of leaf tissue. These fungi are parastic on nine tribes of grasses that have a wide geographic distribution in the western hemisphere. Nine ergot alkaloids belonging to the clavine group have been isolated from four species of Balansiacultured in laboratory media, and several of these have been isolated from parasitized grasses. Ergot alkaloid production by the remaining nine species of Balansiahas not been examined. The endophyte of tall fescue produced both the clavine and ergotamine peptide groups of alkaloids in culture and in the grass. The production of ergot alkaloids by weed grass endophytes is host‐related; therefore, each parasitized weed grass must be assessed for alkaloid production. All isolates of B. epichloe(Weese) Diehl from smutgrass (Sporobolus poiretiiRoem. and Schult.) and 54% of the isolates of B. henningsiana(Moell.) Diehl from broomsedge (Andropogon virginicusL.) produced the following alkaloids in culture: chanoclavine, ergonovine, ergonovinine, and agroclavine. Isolates of these two fungi from other grass genera did not produce alkaloids. While no extensive survey has been done to date, all infected tall fescue examined contains ergot alkaloids. The main peptide alkaloid produced by the tall fescue endophyte is ergovaline. The effects of this peptide alkaloid on cattle have not been determined. However, the total alkaloids produced in culture by B. epichloereduced the serum prolactin levels in cattle and along with prior published accounts on the physiological effects of the clavine and peptide ergot alkaloids, established that these alkaloids can cause toxicity symptoms in cattle consuming infected plant material. Thus, pasture management practices must include procedures that will prevent the growth of grasses that serve as host for endophytic fungi.