Fungal Endophytes of Grasses

Abstract

INTRODUCTIONThe tenn endophyte (Greek: endo == within + phyte = plant) has been defined as an organism contained or growing (entirely) within the substrate plant, whether parasitically or not (100, 106). Using this tenn in its broadest sense, the subject of this chapter could include all fungi that spend all or nearly all of their life cycles in the host grasses. We do not discuss such endophytic fungi as the smuts and vesicular-arbuscular mycorrhizas that infect grass. Instead, our interests lie primarily with a specific group of c1avicipitaceous fungi that belong or are related to fungi in the tribe Balansiae (5, 24). These fungi either are true endophytes that never produce external fructifications on the plant or else may produce external mycelium andlor spores that affect flower and seed production. We focus specifically on those grass-endophyte complexes that may also cause maladies of grazing animals.Using the above criteria, two recent events involving grass-endophyte associations have important implications for the livestock industry. In 1977 Bacon et al (9) reported the close association of an endophyte (Sphacelia typhina) in infected tall fescue (Festuca arundinacea) and the incidence of 293 0066-4286/87/090 1-0293$02.00Annu. Rev. Phytopathol. 1987.25:293-315. Downloaded from www.annualreviews.org by ILLINOIS STATE UNIVERSITY on 10/24/12. For personal use only. Quick links to online content Further ANNUAL REVIEWS 294 SIEGEL, LATCH & JOHNSON fescue toxicosis (summer syndrome) in cattle. A similar association between a then unidentified endophyte in perennial ryegrass (Latium perenne) and the incidence of ryegrass staggers in sheep in New Zealand was reported in 1981 by Fletcher & Harvey (27). Since the initial work of Bacon et al (9) in 1977, researchers have come to further understand the relationship between fungal endophytes of grasses and animal toxicoses. This understanding includes the origin and incidence of infected grasses, modes of dissemination of the fungi, identification of the chemicals responsible for toxicoses, and control of the fungi. Specifically, what has been learned is that endophyte-infected tall fescue and perennial ryegrass are widely distributed in the United States and New Zealand, respec tively; endophytic fungi are only seed disseminated; specific chemicals are responsible for fescue toxicosis and ryegrass staggers; infected pasture grasses cost the livestock producer hundreds of millions of US dollars annually in lost production; the fungi cannot be controlled in the field, but endophyte-free cultivars do result in greatly improved livestock production in the United States; and lastly, the relationship between grass and symbiont is primarily mutualistic. resulting in many benefits to host and fungus (5, 10, 97). With regard to this final point, it is now recognized that these grass endophytes can play an important role in survival of the host plants subjected to environmen tal stresses (insects, grazing animals, drought, and heat). The potential for improved insect resist...

Effects of Endophyte Infection in Tall Fescue (Festuca arundinacea: Poaceae) on Community Diversity

“…Benefits to the fungi include nutrition, long-term protection, and improved dissemination (by seeds) (Siegel et al 1987). Reported host benefits include increased resistance to both grazing and insect herbivory, decreased nematode predation, antimicrobial and antifungal properties, both heat and drought stress tolerance, and increased overall vigor (e.g., tiller production, biomass, height, seed crop, seed germination; Clay 1987Clay , 1990aClay , 1997bCheplick et al 1989;Petroski et al 1990;Guo et al 1992;Siegel 1993).…”

“…Consequently, the majority of grass endophyte studies have dealt with the two widely planted forage grasses, Festuca arundinacea Shreber. (tall fescue) and Lolium perenne L. (perennial ryegrass) and their predominantly mutualistic endophytes (Morgan-Jones and Gams 1982;Siegel et al 1987; 1 Author for correspondence; e-mail spyreas@inhs.uiuc.edu.…”

Fumonisins in Maize: Can We Reduce Their Occurrence?

“…Symptomless infection can exist throughout the plant, and seed-transmitted strains of the fungus can develop systemically to infect the kernels (20,35). By most definitions, this relationship can be referred to as endophytic (52).…”

“…These efforts have met great challenges in the case of tall fescue, because the endophytic fungi are beneficial to their host plants. These benefits include enhanced root development, drought tolerance, and protection against pathogens (52). Therefore, it is very difficult to produce endophyte-free tall fescue populations that retain desirable agronomic characteristics.…”

Is provitamin D a UV-B receptor in plants?

“…Many plants, among them many grasses, harbour endophytic fungi (Clay 1990;Redlin & Carris 1996;Siegel et al 1987), and fungi regularly produce ergosterol as their major sterol. The content of ergosterol in plant tissue has been used as a measure of fungal contamination (Gessner & Schmitt 1996).…”