Endophyte

An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life cycle without causing apparent disease. Endophytes are ubiquitous and have been found in all species of plants studied to date; however, most of the endophyte/plant relationships are not well understood. Endophytes are also known to occur within lichens and algae. Many economically important grasses (e.g., Festuca spp. and Lolium spp.) carry fungal endophytes in genus Epichloë, some of which may enhance host growth, nutrient acquisition and may improve the plant's ability to tolerate abiotic stresses, such as drought, and enhance resistance to insects, plant pathogens and mammalian herbivores.

Transmission

Endophytes may be transmitted either vertically (directly from parent to offspring) or horizontally (among individuals). Vertically transmitted fungal endophytes are typically considered clonal and transmit via fungal hyphae penetrating the embryo within the host’s seeds (e.g., seed transmitting forms of Epichloë). Conversely, reproduction through asexual or sexual spores leads to horizontal transmission, where endophytes may spread between plants in a population or community. Some endophytes that frequently transmit vertically may also produce spores on plants that can be transmitted horizontally (e.g., Epichloë festucae). Some of the Epichloë endophytes have been found to produce a cryptic but infective conidial state on the surfaces of leaf blades. However, the extent to which endophytes rely on these cryptic conidia for horizontal transmission is still unknown. Some endophytic fungi are actually latent pathogens or saprotrophs that only become active and reproduce under specific environmental conditions or when their host plants are stressed or begin to senesce.