Haplotypes distribution and virulence of Gnomoniopsis castaneae in Italy

In the last decades, productivity of Italian chestnut groves has been seriously impacted by the infection of the emerging fungal pathogen Gnomoniopsis castaneae, causing nut rots. Despite the widespread distribution of this pathogen in Italy, its genetic diversity and phylogeographic structure is still largely unexplored. In this study, we analysed the genetic diversity and spatial distribution of G. castaneae haplotypes by investigating 107 isolates from the northwest, the northeast and central Italy, as well as Sardinia. In Sardinia, where little was known about the occurrence of G. castaneae as a nut rot agent, a thorough investigation was conducted in three sites on a total of 1500 nuts. Phylogenetic analyses of sequences of β-tubulin revealed the occurrence at a worldwide scale of two distinct evolutionary lineages (here reported as haplotype A and B), with different frequencies in Italy depending on the geographic area. Based on the outcomes of inoculation experiments on nuts, both haplotypes proved to be pathogenic, although with marked differences in aggressiveness.