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

<i>Epichloë</i> 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 <i>Epichloë</i> endophytes and species of the genus <i>Bromus</i>, a taxonomically complex group characterized by varying ploidy levels and frequent hybridization. Among its sections, <i>Bromopsis</i> includes the highest number of species naturally colonized by <i>Epichloë</i> fungi, while sections <i>Bromus</i> and <i>Ceratochloa</i> show lower infection rates. In South America, endophytes such as <i>E. pampeana</i>, <i>E. tembladerae</i>, <i>E. typhina</i>, and morphotypes of <i>Neotyphodium</i> spp. have been documented in species including <i>B. auleticus</i>, <i>B. brachyanthera</i>, and <i>B. setifolius</i>, 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 <i>Bromus</i> species across the continent. This review synthesizes the current understanding of <i>Epichloë</i>-<i>Bromus</i> 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.