Symbiosis Between Epichloë Fungi and Bromus Grasses: A Review of Current Knowledge and Future Directions

Epichloë is a genus of endophytic fungi that forms systemic, vertically transmitted, and asymptomatic mutualistic associations with grasses in the subfamily Pooideae. These symbioses are non-pathogenic and are of considerable importance in agronomic and livestock systems due to their roles in enhancing host fitness under biotic and abiotic stress. Several studies have reported associations between Epichloë endophytes and species of the genus Bromus, a taxonomically complex group characterized by varying ploidy levels and frequent hybridization. Among its sections, Bromopsis includes the highest number of species naturally colonized by Epichloë fungi, while sections Bromus and Ceratochloa show lower infection rates. In South America, endophytes such as E. pampeana, E. tembladerae, E. typhina, and morphotypes of Neotyphodium spp. have been documented in species including B. auleticus, B. brachyanthera, and B. setifolius, where they appear to contribute to stress resilience. Although most findings originate from Argentina, significant knowledge gaps remain regarding the diversity and distribution of these endophytes in native Bromus species across the continent. This review synthesizes the current understanding of Epichloë–Bromus interactions, emphasizing their ecological and agronomic relevance, particularly in South America. Key factors influencing the establishment of these symbioses are examined, and future research directions are proposed to advance the study of these associations.