Evolution of endophyte-plant symbioses.

Abstract All fungi invading plant foliage have an asymptomatic period in their life cycle that varies from an imperceptibly short period (e.g. pathogens) to a lifetime (e.g. Neotyphodium endophytes in grasses). Endophytic fungus–grass associations are generally treated separately from parasitic, pathogenic and saprophytic interactions and are viewed as mutualistic associations. However, endophyte–host interactions are based on mutual exploitation. Benefits to the partners are rarely symmetric and conflicting selection forces are likely to destabilize them. Unanswered questions are how (i) genetic diversity of the fungus and phenotypic plasticity in fungal life history traits, (ii) genetic combinations between the fungus and the host, and (iii) the fungus and host individually or in concert as a phenotypic unit, respond to changing selection pressures.

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