Assessment of damage potential of Gnomoniopsis castaneae to fruit and trees of European Chestnut (Castanea sativa)

Gnomoniopsis castaneae has become an important pathogen of European chestnut (Castanea sativa), affecting fruits and colonizing shoots and branches, as well as galls caused by the oriental chestnut gall wasp (Dryocosmus kuriphilus). On apparently asymptomatic fruits, G. castaneae can colonize the endosperms, causing quality issues, especially in post-harvest. Given the alarming spread of G. castaneae infections in Italy and the current knowledge gaps regarding aspects of G. castaneae biogeography and virulence, research was addressed to: 1) evaluate occurrence of G. castaneae in chestnut nuts and branches in different Italian regions; 2) study occurrence and distribution of the two known G. castaneae haplotypes throughout Italy; and 3) evaluate their virulence on chestnut under different water regimes. Fungal isolation from representative chestnut branch and nut samples consistently yielded colonies that were morphologically consistent with G. castaneae, the identity of which was confirmed by analysis of ITS sequences. Analysis of β-tubulin sequences confirmed the presence of two distinct genetic lineages (Gc-haplotypes A and B). To assess pathogenicity, G. castaneae isolates were inoculated onto chestnuts, chestnut cuttings and 3-year-old young plants grown under two water regimes. All assessed isolates were pathogenic on chestnut, and water-stressed plants exhibited more extensive necrosis than well-watered plants when inoculated with the Gc haplotype A, highlighting the influence of environmental conditions on disease expression. This study expands current knowledge on the distribution, genetic diversity, and effects of water stress on the pathogenic potential of G. castaneae on chestnut.