Assessing the Genetic Variability of Sweet Chestnut Varieties from the Tuscan Apennine Mountains (Italy)

Castanea sativa Mill. is a valuable species with historical and economic importance in Europe, particularly in the Mediterranean area. In Italy, chestnut cultivation has been developed for centuries, leading to the recognition of more than 300 varieties. Nevertheless, a profusion of local names has been assigned by growers, causing the occurrence of synonyms and homonyms across the country. This research focused on genetic characterization and identification using 21 single sequence repeats (SSRs) for four chestnut varieties (i.e., Pastinese, Nerattino, Carpinese, and Rossola) commonly used for flour production in the Tuscan Apennine Mountains (Pistoia Province). A comprehensive number of 55 accessions identified by local growers as belonging to the four varieties were analyzed, in addition to a few "Marrone" accessions as outgroups. The 21 microsatellites were highly informative, detecting 98 alleles and displaying an average polymorphism information content (PIC) equal to 0.582. In addition, a considerable amount of genetic diversity was revealed, as shown by the heterozygosity levels (He = 0.634 and Ho = 0.475). The STRUCTURE analysis provided clear distinctions among the different varieties, splitting them into four separate groups. This result was also confirmed by UPGMA dendrogram and principal co-ordinates analysis (PCoA). However, one accession (Carp_5), previously identified as Carpinese, showed an allelic profile attributable to Pastinese, suggesting that farmers might have performed mislabeling or grafting propagation errors. Thus, our results confirm the use of SSRs to allocate the accessions of different varieties, uncovering possible synonyms and homonyms. Specifically, in the context of the Pistoiese mountain region, this tool can favor the traceability of processed products, such as flour, enhancing the quality and economic value of the local market. Lastly, our findings have revealed a considerable genetic variability within the Tuscan chestnut varieties whose preservation is mandatory to face climate change challenges through sustainable forest management practices.