Stomatal traits in pomegranate (Punica granatum L.): varietal and seasonal variability in relation to climatic adaptation

This study, conducted in the Puglia region over the 2019–2020 period, investigated the variability of stomatal traits in 77 pomegranate (Punica granatum L.) varieties, including both local and internationally cultivated varieties. All varieties were grown in the germplasm repository of the Department of Soil, Plant and Food Sciences (DiSSPA), located at the 'Martucci' experimental station in Valenzano (Bari, Italy). The aim of the study was to identify stomatal traits, specifically stomatal density (SD) and stomatal size (SS), to be used for further studies. Leaf samples were collected in summer from three plants per variety. To obtain epidermal impressions, a layer of clear nail polish was applied to the abaxial leaf surface, allowed to dry, and then peeled off using transparent adhesive tape. The imprint was transferred to a microscope slide and observed under a light microscope. No stomata were detected on the adaxial surface of the leaf. The results revealed significant differences among varieties, with SD ranging from 384 stomata/mm² in ‘De Marco’ to 756 stomata/mm² in ‘Reddito Dolce’. SS ranged from 120 μm² (in ‘A Dente San Giorgio’ and ‘Capurso Acido Surico’) up to 273 μm² (in ‘Perek Ischkjily’). The analysis also revealed significant differences in the two seasons, with consistently lower SD and SS values recorded in 2019 compared to 2020. The considerable variability observed among varieties, such as the high SD in ‘Reddito Dolce’ and the large SS in ‘Perek Ischkjily’, suggests the potential for selecting genotypes best suited to different climatic conditions. These findings provide valuable insights for selecting/breeding strategies aimed at enhancing pomegranate resilience under conditions of limited water availability and high temperatures. Further studies will be conducted to better understand the relationship between stomata traits and physiological, yield and quality parameters of pomegranate varieties.