The presence of a fungal endophyte (endo = inside, phyte = plant) in tall fescue can limit animal productivity even though it enhances the grass’s ability to persist. Endophytes produce compounds like peramine, lolines and ergot alkaloids. Each of these provides protection against some insects, but the ergot alkaloids also cause toxicity to mammals. Telltale signs of ergot alkaloid poisoning include rough hair coats in summer, overheating indicated by congregating in shade or ponds, excessive urination or necrosis of extremities (fescue foot) (Figure 1). Fescue toxicosis has been known for decades, but tall fescue’s persistence has perpetuated its use in pastures.
In the 1940s and 50s, poor animal productivity was observed with cattle grazing fescue pastures. The symptoms seen in cattle were similar to toxicity from ergot, a fungal contaminant of rye called Claviceps purpurea that replaces seed with ergot structures. Ergot is full of compounds (ergot alkaloids) that cause vasoconstriction and hallucinations, hallmarks of ergotism, a disease known from as early as the Middle Ages as Saint Anthony’s Fire. However, it was clear that Claviceps was not the problem in tall fescue. By the 1970s, scientists were able to document that pastures causing fescue toxicosis were infected with a fungal endophyte that produces the ergot alkaloid, ergovaline.
Ergot alkaloids accumulate when an endophyte’s genetic code directs their production. The genome of Epichloë coenophiala from Kentucky 31 shows genes that encode steps for ergot alkaloid production. When these genes are present and active, alkaloids concentrate in structures where the fungus lives in the plant, such as in the inflorescence, seeds or base of the tillers. Consequently, there is some seasonality of when ergot alkaloid production is highest. Peak ergot alkaloid production usually occurs in early summer during seed production, so clipping seed heads can reduce the dose of toxic alkaloids to livestock. Likewise, there is less endophyte in the blade of the grass versus the base of the tiller, so it is important not to let the animals graze too low.
The endophyte in Kentucky 31 tall fescue produces ergovaline (Figure 1), but scientists have also identified endophytes that do not produce this toxin. How can certain endophytes be nontoxic yet others produce dangerous side effects? The unseen difference lies in the unique genetic code for each endophyte strain. Next month we will discuss tall fescue cultivars with novel endophytes.
Figure 1: Ergot alkaloids produced by the fungus Epichloë coenophiala cause fescue toxicosis. Right: Structure of the ergot alkaloid ergovaline. Left: Cattle showing symptoms of fescue toxicosis caused by ergot alkaloids.
About the Authors: Dr Carolyn Young runs the Mycology lab at the Noble Research Institute. She has a passion for working with endophyte infected-grasses and understanding the important role they have in forage-based systems. She works closely with the Noble Research Institute grass breeder, Mike Trammell, on the development of new tall fescue cultivars that are safe for grazing livestock. The Noble Research Institute developed and released Texoma MaxQ II. Amy Flanagan is a research associate in the Mycology lab at the Noble Research Institute.
The Alliance for Grassland Renewal is a national organization focused on enhancing the appropriate adoption of novel endophyte tall fescue technology through education, incentives, self-regulation and promotion. For more resources or to learn more about the Alliance for Grassland Renewal, go to www.grasslandrenewal.org
The Alliance for Grassland Renewal 