Tropical fungal endophytes represent a novel system for exploring symbionts as mediators of plant resistance to pathogens. This study will investigate the previously undescribed diversity of tropical fungal endophytes and their interactions in a forest plant-pathogen system. Fungal endophytes, the diverse, asymptomatic Ascomycetes that inhabit aerial plant tissues, are remarkably rich in the leaves of tropical trees. Given that endophytes are heterotrophs and likely exert a cost upon the host, and that tropical trees are well-defended chemically against a diversity of fungi, why do tropical trees harbor such a richness of fungal endophytes? This dissertation research will test the hypothesis that endophytes act as mutualists by enhancing host plant resistance to fungal pathogens. At Barro Colorado Island, Panama, endophyte communities on Trichilia tuberculata (Meliaceae), a common canopy tree will be quantified and compared to other host tree species. In vitro assays will assess the influence of endophytes on the growth and survival of the undescribed Ascomycete that causes shot-hole disease in T. tuberculata, while in vivo growth chamber experiments will assess the costs and benefits of endophyte infection in the presence and absence of the pathogen. This study will enhance our understanding of both host-symbiont-pathogen interactions and fungal biodiversity.
