Cultivable Foliar Endophytic Fungal Community in Endemic Mexican Quercus Species Across a Forest–Avocado Orchard Landscape

Temperate oak forests are biodiversity-rich ecosystems, and Mexico is a major center of diversification for Quercus, with high levels of endemism. In Michoacán (central Mexico), the rapid expansion of avocado cultivation has reduced oak forest cover and increased landscape fragmentation. Foliar endophytic fungi can contribute to host performance under biotic and abiotic stress, yet their diversity in endemic Mexican oaks and their response to land-use change remain poorly characterized. Here, we characterized the cultivable foliar endophytic fungal communities associated with Quercus castanea and Quercus obtusata along a forest–avocado orchard cover gradient. We isolated 112 endophytic fungal strains from leaves of Q. castanea (n = 56) and Q. obtusata (n = 56). All isolates belonged to Ascomycota and were assigned to four classes, 10 orders, and 32 genera based on nrITS sequences and genus-level phylogenetic analyses. The most abundant genera were Nigrospora (8%), Xylaria (7%), Nodulisporium (6%), and Daldinia (6%). Patterns of genus exclusivity and richness indices consistently showed higher diversity in forest-dominated landscapes than in orchard-dominated sites. Overall, our results indicate that forest-to-orchard conversion is associated with shifts in the structure of the cultivable foliar endophytic fungal communities of oak species and with a tendency toward reduced diversity in more disturbed landscapes. Further studies integrating culture-dependent and culture-independent approaches are needed to evaluate the functional implications of these patterns for host health and ecosystem resilience.