Importance and economic significance of the Acremonium endophytes to performance of animals and grass plant

Abstract

Although fungal endophytes of grasses have been known since the 1930s, their economic importance was not recognized until an association was made in the late 1970s between Acremonium coenophialum Morgan-Jones and Gams and a toxicity syndrome in livestock consuming tall fescue ( Festuca arundinacea Schreb.). Cattle consuming endophyte-infected tall fescue have reduced growth, conception, milk production, and intolerance to heat. In horses, high foal mortality and agalactia occur on endophyte-infected grass. Sheep consuming perennial ryegrass ( Lolium perenne L.) infected with the endophyte Acremonium lolii Latch, Christensen and Samuels are afflicted with a staggers syndrome, resulting in reduced weight gain. Endophyte-free, as compared with infected tall fescue, can increase steer weight gains by 30 to over 100% and furnish normal conception and milkproduction in beef cows. Since most tall fescue pastures in the USA are infected with the endophyte, livestock economic losses are high. Beef cattle annual losses are conservatively estimated at $354 million in reduced calf numbers and $255 million in reduced weaning weights. The poor performance of beef steers on infected tall fescue pasture has prevented its use for stocker production, resulting in higher production costs on high-quality winter annual pastures. Foal mortality of mares grazing tall fescue can be high, but no estimate of losses is available. Wild rabbit populations are reduced when consuming tall fescue. The mutualistic symbiosis of the endophyte and the grass confers a number of benefits on the host plant such as insect and nematode resistance, drought tolerance, and improved competition with other plant species. Endophyte infection of turf grasses confers improved growth and resistance to environmental stresses. In contrast, the use of endophyte-free grass cultivars for improved animal performance results in plants less tolerant of pests, drought, and overgrazing. Stand losses of endophyte-free tall fescue have been greatest on farms in the southern part of the USA tall fescue belt where environmental stresses are greatest. Better grazing management practices are necessary to maintain stands and productivity of endophyte-free grass cultivars. Ideally, modification of the fungal endophyte to remove the harmful properties and maintain those beneficial to the host plant is the ultimate solution. The increasing number of scientists from many disciplines attracted to research on the grass-endophyte relationship offers much promise for the future.