Long-lived trees accumulate somatic mutations during growth, making them useful for studying DNA changes over time. Chestnut (Castanea spp.) is a good model due to its longevity and clonal propagation. This study estimated mutation rates in a 130-year-old Marrone Avellinese tree and compared them with grafted clones. Results show mutations increase with growth, but grafted trees have fewer mutations, suggesting a "grafting reset effect". This highlights how grafting may limit mutation buildup and supports SNP-based tools for cultivar identification.