Identifying and characterizing Gnomoniopsis castanea isolates from active blight cankers and wasp galls in Castanea sativa on Madeira Island

This study is the first to report the occurrence and ecological characteristics of Gnomoniopsis castanea on Madeira Island. The European chestnut ( Castanea sativa Mill.) has been cultivated on the island since the 15th century and remains economically important. However, chestnut production is increasingly threatened by pathogens such as chestnut blight ( Cryphonectria parasitica ) and pests like the chestnut gall wasp ( Dryocosmus kuriphilus ). In recent years, G. castanea has emerged as a significant pathogen associated with nut rot, bark cankers, and necrotic lesions. Here, we assessed the microfungal communities associated with active C. parasitica cankers and D. kuriphilus galls, with a focus on detecting the presence of G. castanea . Surveys conducted in two chestnut groves (Jardim da Serra and Curral das Freiras) yielded 210 samples and 194 fungal isolates, primarily from the phylum Ascomycota. The most abundant families were Cryphonectriaceae (61.9%), Graphostromataceae (9.8%), and Gnomoniaceae (7.2%). G. castanea was identified in 14 isolates; 10 of these were characterized morphologically and confirmed through ITS and TEF1-α gene sequencing. Phylogenetic analysis of the ITS region revealed high genetic similarity among the Madeiran isolates. The detection of G. castanea in both cankers and galls suggests it may persist in chestnut tissues as an endophyte.