Pistacia vera and P. integerrima Hybrids for Pistachio Rootstock: Seed set, Seedling Survival and Early Growth Evaluation under Chilling Temperature

Interspecific hybrid rootstocks have the potential to improve the productivity and resilience of pistachio orchards in response to environmental stresses. This study aimed to produce inter-specific hybrids between P. vera and P. integerrima (In) and compare their early growth with their parents under chilling temperatures. Controlled pollination using In pollen was conducted on five pistachio cultivars including Kaleh-Ghuchi , Khanjari-Ghermze , Akbari , Khanjari-Sefid , Ohadi and a local variety. The fruit set in female parents through controlled pollination of interspecific crossings was significantly lower than natural open pollination, resulting in a high percentage of blank seeds. Only Khenjari-Ghermze and Kalleh-Ghoochi produced a sufficient number of seeds for further experiment. The germination and survival rate of hybrid seeds were lower than that of pistachio cultivars (P 0.01). Growth parameters of hybrid seedlings and their parents were examined at 5 °C and 25 °C. All rootstocks showed a significant reduction in growth at low temperatures, with chlorophyll and chlorophyll fluorescence also decreasing significantly at 5 °C. Overall, In seedlings showed more growth at 25 °C than other rootstocks, and inter-specific hybrids showed better growth characteristics than seedlings obtained from pistachio cultivars. In seedlings growth almost stopped at 5 °C, but pistachio seedlings continued growing despite the low temperature. In most traits, hybrid cultivars were intermediate between their parents, indicating the suitable inheritance of growth characteristics from In and cold resistance from P. vera. The hybrid between Khanjari-Ghermze ×In showed good growth in the early growing stages under chilling temperature and could be a suitable rootstock for further research on interspecific hybrid.