Protective Grass Endophytes: Where are they from and where are they going?

Abstract

erhaps the most widely used agents of biological plant protection are endophytic fungal symbionts (endophytes) of forage and turfgrasses. These are fungi of the family Clavicipitaceae, which grow between host cells in vegetative tissues, ovules, and seeds of systemically infected grass plants. The existence of these endophytes was not fully appreciated until recent years, although the protection they provide against insect damage (Fig. 1) and drought contributes to the superior agronomic qualities of favorite pasture grasses in North America, Australia, and New Zealand. Unfortunately for livestock farmers, these endophytes also provide a degree of protection from grazing mammals. In 1977, Bacon et al. (2) reported that the grass Festuca arundinacea var. genuina Schreb. (hexaploid tall fescue) had a fungal endophyte related to Epichloe typhina (Pers.:Fr.) Tul., and that this endophyte— now known as Neotyphodium coenophialum (Morgan-Jones & Gams) Glenn, Bacon, & Hanlin—was responsible for toxicosis suffered by livestock grazing the grass. Epichloe species were known for many decades (44), but reports relating that nonpathogenic endophytes could be detrimental to livestock provided new impetus for intensive studies, making the grass–endophyte associations among the best characterized symbioses in biology. Less than two decades of research have yielded a rich body of knowledge about these symbioses: their secondary product chemistry, ecology, evolution, genetics, and molecular biology; their ecological roles as protectants from insect and vertebrate herbivores, pathogenic fungi and nematodes, and drought; and their effects on host growth and competitiveness. The endophytes produce numerous alkaloids, some of which are unrelated to any known from plants or other fungi. Their genetic and evolutionary complexity is extraordinary. They were the first fungi genetically documented as interspecific hybrids (47,53). Meanwhile, molecular genetic techniques were applied to the endophytes of tall fescue and other grasses, bringing us closer to the prospect of reducing or eliminating their toxicosis to livestock while continuing to employ their bioprotective qualities.