ABSTRACT

Grass symbionts of the genus Epichloe, including related asexual fungi, can be important for biological protection of their hosts under stresses imposed biotically (e.g., herbivores and parasites) or abiotically (e.g., drought). The symbionts can be categorized as three types. The most benign (nonpathogenic) type encompasses symbionts that only transmit vertically by systemic infections of seeds and tend to be highly beneficial to their hosts. In these cases, the symbiont is asexual (thus taxonomically classified in genus Neotyphodium). In contrast, the most antagonistic Epichloe species only transmit horizontally (i.e., contagiously), completely suppress host seed production, and are obligately sexual. In the third type, balanced (pleiotropic) symbiosis, the symbiont aborts some host inflorescences, is transmitted both horizontally and vertically, and, like the benign type, can greatly enhance host fitness. In balanced symbiosis, both host and fungus have a sexual stage in addition to their asexual reproductive capabilities (Fig. 1 ).