A lush green tall fescue pasture can often hide an unseen dark side. Many livestock producers recognize that although tall fescue is considered a quality forage, the presence of a fungal endophyte (endo = inside, phyte = plant) can limit animal productivity. Unfortunately, most fescue grown in the United States (largely the Kentucky 31 variety) is infected with an endophyte that causes toxicity (fescue toxicosis) to grazing livestock, due to production of compounds called ergot alkaloids. Fescue toxicosis results in lower average daily gains and reduced fertility of livestock, causing economic loss and limiting producer profitability.
The endophyte found in tall fescue is a fungus called Epichloë coenophiala. This fungus forms a symbiotic relationship with the plant. A symbiosis is a close relationship between two species where at least one species will benefit. The grass is the most visible member of this symbiotic partnership. However, if you use a microscope, you can readily see the fungus in the seed or in a tiller when you stain the sample with a dye (Figure 1). The endophyte gains a home, lives its whole life in the plant and only transmits to the next generation by colonizing the seed. Trapped inside its plant, the endophyte is unable to infect other plants. New endophyte-infected tall fescue plants only arise from seed produced from other endophyte-infected plants.
If the endophyte gets a place to live, what benefit does the plant get? The endophyte provides natural insect protection and can improve drought tolerance and nutrient uptake, providing endophyte-infected fescue with a selective advantage that results in greater persistence over endophyte-free tall fescue. The presence of the endophyte is one of the reasons why tall fescue is so persistent and widely distributed in the United States.
Fortunately, not all endophytes, like the one found in Kentucky 31, are detrimental to livestock. Recently developed cultivars are established with endophytes that make the grass more palatable without the concerns of causing fescue toxicosis. Next month, we will learn more about fescue toxicosis and 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