Host Preference and Seasonal Variation in The Colonization of Tubakia s.l. Associated with Evergreen Oak Species in Eastern Japan

Foliar fungal endophytes are ubiquitous and hyperdiverse, and tend to be host-specific among dominant forest tree species. The genus Tubakia s.l. comprises foliar pathogens and endophytes that exhibit host preference for Quercus and other Fagaceae species. To clarify interspecific differences in ecological characteristics among Tubakia species, we examined the endophyte communities of seven evergreen Quercus spp. at three sites in eastern Japan during summer and winter. We also compared their spore germination rates at different temperatures. Host tree species was the most significant factor affecting endophyte community composition. The Tubakia species found at the study sites were divided into five specialists and three generalists according to their host ranges. Specialists were dominant on their own host in summer, and their dominance declined in winter. In contrast, generalist Tubakia species 3 became dominant in some tree species in winter. This seasonal variation in Tubakia species dominance was consistent with their cold tolerance, which was evaluated in spore germination tests. This is the first study to report ecological differentiation among endophytic fungal species within a genus.