Acremonium endophytes in perennial ryegrass and other pasture grasses in Australia and New Zealand

Many grasses contain asymptomatic fungal endophytes which are now recognised as having a major impact on the performance of pastures in Australia and New Zealand, and elsewhere in the world. The association between the plant and the fungus is regarded as mutualistic, with the host grass able to benefit from endophyte presence through reduced herbivore feeding, increased resistance to insects, improved plant growth and possibly disease resistance. Grazing systems may be disadvantaged, however, as the ingestion of endophyte-infected grasses can be associated with a number of animal toxicoses including ryegrass staggers and fescue toxicosis. There is increasing evidence that the effects of endophyte on the host grass, and consequently on pasture performance and animal production, are mediated by a range of secondary metabolites produced by the plant-fungus interaction. Recent work has shown that a great deal of variation can be found amongst endophyte strains both in the types and amounts of these secondary metabolites produced. This review presents the current status of knowledge on the impact of endophyte on pasture grasses in Australia and New Zealand and attempts to place it in the framework of endophyte research in general. It discusses the potential for harnessing the benefits of endophyte infection, whilst minimizing deleterious effects, through the use of elite endophyte strains which have been isolated from naturally occurring grasses, or modified by the techniques of genetic engineering. It concludes by identifying a number of significant areas which require further research for us to fully understand the plant-fungus interaction and its effects on pasture systems.