Epichloë Endophytes: Clavicipitaceous Symbionts of Grasses

Abstract

The modern approach to biology emphasizes the workings and system integration of individual organisms, with microbial infections usually considered in a disease context, yet it is benign and mutualistic symbioses that actually dominate the biosphere. Even our own healthy bodies host complex microbial consortia (Gill et al. 2006). The ecological importance of lichens (fungi hosting green algae or cyanobacteria; DePriest 2004) and the reliance of corals on zooxanthellate algae (Baker 2003) are clear. Root nodules, representing symbioses of legumes with rhizobia (Rhizobium spp. and related bacteria; Doyle 1994), provide a large portion of fixed nitrogen on which much of the biosphere relies. Even more ubiquitous are the mycorrhizae, which serve a key nutritional role in the vast majority of land plants (Strack et al. 2003; Chaps. 13, 14). These symbioses are readily apparent to the unaided eye. For example, lichens coat rocks and tree trunks in much of earth’s wilderness, and algae bestow their bright colors upon vast coral reefs. More sophisticated microbiological techniques must be employed to visualize endophytic and epiphytic microbes, and often the structures observed need much further investigation to determine if they represent benign symbionts or latent plant pathogens.