ACREMONIUM ENDOPHYTES - OUR CURRENT STATE OF KNOWLEDGE AND FUTURE-DIRECTIONS FOR RESEARCH

Current knowledge of grass-Acremonium associations results from the discovery that animals grazing on infected grasses show an array of debilitating symptoms which lead to severe economic losses. Acremonium endophytes occur worldwide, infecting many cultivated and wild pooid grasses. It is also apparent that parasitism of different grasses by these fungi is complex. The fungal symbiont may be completely or partially endophytic and expression of parasitism may range from agonistic (the pathogenic phase of Epichloe typhina (Pers.) Tul.) to mutualistic. Regardless of how symbiosis is expressed, the associations can often benefit host grasses, improving their growth and survival. In addition, much information has been gained on the biology, ecology and physiology of specific grass-endophyte associations, the effects of infected (E+) grasses on herbivores (vertebrates and invertebrates), the chemistry of alkaloids responsible for herbivore resistance, tolerance of E+ grasses to drought, and the management of endophytes for the benefit of turf and pasture grasses. Present information strongly suggests that most grass-endophyte symbioses must be maintained for optimum survival of the host grasses. Future research efforts can be clearly defined, on a practical basis, as a continuation of studies that may lead to alleviation of toxicity to grazing animals, and the development of E+ grasses suitable for turf and pasture use. These goals may be accomplished by manipulation of either livestock, endophyte or grass via genetic engineering, conventional breeding practices, or natural selection. Other approaches include improved plant and animal management and the use of chemical antidotes to reduce animal toxicoses. Specific research goals include continuation of studies on the biology, ecology, and physiology of symbiosis in cultivated and wild species of grasses. These studies should aid in elucidating the role of the symbionts in the host-fungus interactions (nutrition and metabolism) and mutualistic versus agonistic expression, as well as the origin and coevolution of the symbionts, mechanisms of biosynthesis of alkaloids, the bases for improved plant growth and resistance to biotic and abiotic stresses, and development of techniques for genetic manipulation of the symbionts. Pathophysiology studies using pure alkaloids, small animal bioassays, in vitro organs, tissue culture, and indicators of biochemical activity (enzyme and hormones) will clarify the mechanisms of alkaloid toxicity, potentially leading to chemical antidotes and improved systems of animal management to alleviate toxicoses. Through the interdisciplinary research that has characterized this field, great strides have been made in understanding the role of Acremonium endophytes in animal toxicoses and the stress survival of E+ plants.