Gnomoniopsis castanea sp. nov (Gnomoniaceae, Diaporthales) as a causal agent of nut rot in sweet chestnut

The genus Gnomoniopsis (Gnomoniaceae, Diaporthales) is currently composed of 13 endophytic and/or parasitic species on plants in the Fagaceae, Onagraceae and Rosaceae families. Species definition is based on a combination of morphological traits, association with specific plant hosts, and phylogeny. In this paper a new species (G. castanea sp. nov.) is proposed based on its association with Castanea sativa (a plant species never reported to be infected by fungi belonging to this genus), on its morphology, and on phylogenetic analysis based on the ITS region of ribosomal DNA and on the EF1-α locus. The fungus is consistently associated with nut rot and caused the disease when artificially inoculated in the fruits or flowers. Disease incidence varied depending on the orchard and the year and attained up to 83% of nuts in some areas of North-western Italy. The fungus was also consistently isolated from the bark of asymptomatic branches in naturally infected chestnut orchards.