The Dormancy of Natural and Unnatural Aging in Pistacia khinjuk Stocks Seeds

The concept of physiological maturity refers to the period during which seeds reach their maximum germination capacity. Accurately determining this stage facilitates efficient seedling production and helps balance supply and demand. Although seed storage conditions and duration are known to affect physiological dormancy, obtaining the desired number of rootstocks from Pistacia khinjuk Stocks (buttum) remains constrained by currently low germination rates. In this study, we assessed the effects of natural (25°C) and unnatural (4°C) aging storage conditions on physiological dormancy by evaluating the germination of newly harvested seeds alongside seeds stored for 1, 2, 3, and 4 years at 4°C and 25°C. To elucidate the underlying mechanisms, germination data were correlated with endosperm starch content, β -amylase activity, and the levels of abscisic acid (ABA) and gibberellic acid (GA ₃ ) in the embryo. Our results indicated that the highest germination rate (81%) was achieved in newly harvested seeds without any dormancy-breaking pretreatment. Prolonged storage at 25°C over 4 years led to a significant decrease in endosperm starch content (from 56 to 29.71 mg/g) and a concurrent increase in β -amylase activity (from 10.95 to 26.86 EU/g). Furthermore, the ABA/GA ₃ ratio dropped remarkably from 5.05 ng/g in newly harvested seeds to 0.89 ng/g in 3-year-old seeds. Storage temperature did not significantly affect germination rates. Interestingly, although the enzymatic and hormonal shifts observed during storage typically favor dormancy release, germination rates did not increase. These findings suggest that newly harvested P. khinjuk seeds do not exhibit deep physiological dormancy, and that natural aging, despite inducing favorable biochemical changes, does not enhance germinability.