Acremonium in fescue and ryegrass: boon or bane? A review.

The research article discusses the effect of a specific type of fungus, Acremonium, on the performance of livestock fed with fescue and ryegrass. It suggests that while removing the fungus can enhance animal productivity, it also unfortunately weakens the grasses’ ability to fight off insects, diseases, and withstand drought.

Understanding the Role of Acremonium Fungus

• The research opens by pinpointing Acremonium coenophialum Morgan-Jones and Gams as a common fungus found in tall fescue. The study suggests that the presence of this fungus is responsible for the poor performance of animals such as beef cattle and horses that feed on this grass.
• The researchers further discuss a similar fungus, A. lolii Latch, Christensen and Samuels, which infects ryegrass and has been linked with causing a neurological disorder in sheep known as ryegrass staggers.

Attempting to Improve Animal Performance

• To mitigate these issues, researchers have experimented with using fungus-free (referred to as E-) cultivars of fescue and ryegrass. Although these fungus-free versions of grass did enhance the performance of the livestock that consumed them, the grasses themselves suffered, showing reduced productivity and an inability to maintain their populations in the long term.

Deterioration of Fungus-Free Grasses

• The study highlights that E- tall fescue is susceptible to numerous stresses such as attacks from insects, diseases, root predation by nematodes, and drought stress, leading to its population decline.
• Contrarily, Acremonium fungus assists the fescue in resisting these challenges. For example, the presence of the fungus stimulates the fescue to produce a disease-fighting enzyme called chitinase. Similarly, fescue plants hosting this fungus show greater resistance to nematodes due to the thickening of the root endodermal layer.

Role of Acremonium in Drought Resistance

• With drought identified as the number one cause of E- fescue population decline in certain parts of the U.S., the study details how the presence of Acremonium endows the host plant with adaptive morphological and physiological changes that enhance its drought resistance.
• These changes include greater leaf rolling, leaf senescence, stomatal closure, and osmotic adjustment. The research also suggests that the fungus may enhance the production of certain plant hormones like abscisic acid, which could mediate these drought resistance mechanisms.

Benefits of Endophyte-Infected Fescue

• The paper concludes that despite their negative impact on certain types of livestock, fescue plants hosting Acremonium endophyte exhibit enhanced productivity and competitiveness over those that are endophyte-free. These benefits may include improved germination, proliferation of shoots or tillers, and overall biomass production per tiller.