Unique tree: Foliar endophytic fungi of the critically endangered Andreadoxa flava (Rutaceae) in Brazil.

Endophytes are unique organisms that may protect their host from abiotic and biotic stress and represent a hidden reservoir for biotechnological and diversity/taxonomic studies, mainly in a megadiverse country like Brazil. Andreadoxa flava, a remnant species of the Atlantic Forest with a single known tree, is considered extinct in the wild. Here, we assessed the culturable endophytic fungal community from leaves of this last remaining tree found in a cabruca agroforestry system. We obtained 296 isolates and a richness of 29 taxa based on morphology and DNA sequence analysis. Endophytes were classified in eight orders of Ascomycota Glomerellales (35.82%), Diaporthales (25.59%), Xylariales (21.95%), Botryosphaeriales (14.52%), Pleosporales (1.01%), Sordariales (0.67%), Hypocreales (0.33%), and Eurotiales (0.33%). The most dominant genera were Colletotrichum (105 isolates), Diaporthe (75 isolates), and Phyllosticta (41 isolates). The Shannon index (1st Collection: H = 2.434 and 2st Collection: H = 2.22) suggests a relatively high diversity. Additionally, we discuss the conservation implications of the fungal community in light of its host's imminent extinction. These results suggest that endophytic fungi associated with critically endangered plant species represent a promising frontier for mycodiversity, biotechnological exploration, and ecosystem conservation, offering a novel pathway to safeguard microbial diversity within threatened biomes.