Endophytism

Endophytism refers to a symbiotic association in which endophytes inhabit the internal tissues of a host plant without causing apparent disease. The term encompasses fungi and bacteria that reside in roots, stems, leaves, and seeds, often in a systemic, long-term relationship. Endophytes may act as mutualists, benefiting the plant through growth promotion or stress tolerance, or as commensals, with no obvious effect, and in some contexts may have latent pathogenic potential.

Fungal endophytes are especially well studied, with many Ascomycota colonizing intercellular spaces and, less commonly, intracellular sites. Bacterial endophytes also inhabit the endosphere and can influence nutrient status and defense. Transmission can be vertical through seeds, promoting co-evolution, or horizontal via environmental propagules, depending on the species and host.

In grasses, endophytism is prominent. Epichloë and its asexual relatives (formerly known as Neotyphodium) form systemic infections that are usually vertically transmitted via seeds. These endophytes produce secondary metabolites such as alkaloids that deter herbivores and pathogens, contributing to plant defense and agricultural persistence. In tall fescue and other pasture grasses, the plant-endophyte mutualism has both benefits and drawbacks for livestock and ecosystem management.

Ecological and practical significance: Endophytes can enhance drought tolerance, nutrient acquisition, and resistance to pests; however, alkaloid production can pose risks to grazing animals and necessitates management strategies and breeding of non-toxic or reduced-toxicity strains. Endophytism also influences plant diversity and ecosystem function, and is a focus of biocontrol and plant-microbe interaction research.

Detection and study rely on microscopy, culture-based methods, and molecular techniques such as ITS sequencing and metagenomics. Understanding endophytism informs ecology, evolution, and agricultural applications, highlighting the spectrum from mutualism to latent pathogenicity.