The biology of the endophyte/grass partnership

The association of Epichloë and Neotyphodium endophytes with host grasses is one of balance between both partners. The host plants are symptomless with the exception of stromata that can form on reproductive tillers of grasses infected with Epichloë spp. The hyphae of the endophytes, spread systemically throughout the above ground parts of plants and in leaves, are aligned parallel with the longitudinal leaf axis and are seldom branched. In this review, the reader is guided through the interaction of host grass and endophytes as revealed by microscopy and then given a model to explain the unique association that these endophytic fungi have with host grasses. This model proposes that hyphae within meristematic tissue branch profusely, providing hyphal strands that extend by intercalary growth amongst enlarging plant cells. Hyphae cease branching and elongating when amongst stationary cells but remain metabolically active, producing a range of bioactive products that enhance the persistence of host grasses. By this process the synchronisation of endophyte and plant growth is achieved, providing a generally mutualistic relationship. Keywords: Neotyphodium, Epichloë, intercalary hyphal extension