Sirococcus smithogilvyi: haplotype diversity in Basilicata Region (Southern Italy)

Chestnut phytosanitary emergencies are rising in recent years also due to climate changes, which allow new treats to find favourable environmental conditions in previously unsuitable places and the rapidity of movements which aids their survival. Among the emerging fungal pathogens, Sirococcus smithogilvyi the causal agent of chestnut brown rot (CBR), a very damaging chestnut disease, stands out. Between 2023-2024, S. smithogilvyi was frequently isolated from 1200 nuts collected randomly in three chestnut locations of Basilicata region (Southern Italy) and initially identified based on morphology features. Other fungal taxa were less frequently isolated: Alternaria alternata, Botrytis cinerea, Penicillium sp., Neofusicoccum parvum, Mucor sp., Cladosporium sp. and Trichoderma sp. Sequencing of two common fungal barcodes, the Internal Transcribed Spacer (ITS) region of ribosomal DNA and the β-tubulin (tub2) gene confirmed the morphological identification. Furthermore, phylogenetic analyses of S. smithogilvyi isolates, based on tub2 nucleotide sequences, showed the occurrence of two separate evolutionary lineages in Basilicata, previously recognized as haplotypes A and B. The haplotype A, was predominant registering 86% frequency while the haplotype B registered only a 14% frequency. The prevalent presence of S. smithogilvyi haplotype A (reported to be more aggressive) along with other additional factors could explain the serious damage and the chestnut production losses recorded for the past years in Basilicata, which urges to find and implement suitable measures to control this emerging and very damaging chestnut pathogen.