Optimization of temperature and parental effects on seed germination and seedling growth in pistachio varieties

Pistachio (Pistacia vera L.) is a temperate and semi-arid tree crop of growing economic importance worldwide, yet new cultivar development is needed to enhance adaptation to diverse growing environments. Optimizing seed germination and early seedling growth is essential for accelerating breeding programs in long-generation tree crops such as pistachio. This study aimed to (i) determine the optimal temperature for seed germination and (ii) evaluate the effects of female parent, field origin, and seed weight on germination, seed emergence and seedling performance.

Seed from open-pollinated pistachio cultivars were collected from experimental orchards in southern Spain and subjected to controlled germination conditions. Five temperature regimes (5, 20, 24, 28, and 32 °C) were tested, and germination percentage, germination velocity index (GVI) and radicle growth were monitored over time.

Temperature was the main factor influencing germination and radicle growth. No germination occurred at 5 °C, whereas the highest germination percentage and maximum radicle growth were recorded at 28 °C. Temperatures between 20 °C and 32 °C showed similar final germination rates, although early germination was faster at higher temperatures. Female parent significantly influenced seedling growth but had limited effects on emergence percentage. 'Kalehghouchi', 'Lost Hills' and 'Kastel' exhibited superior seedling vigor, while 'Larnaka' and 'Joley' showed lower performance. Field origin had a minor effect on germination but significantly affected later seedling growth, suggesting that seed origin, through a combination of environmental and genetic factors, may influence seed physiological quality. Seed weight differed among cultivars and was positively correlated with seedling growth, but not with germination percentage. Overall, results demonstrate that germination in P. vera can be efficiently achieved without complex dormancy-breaking treatments under optimal temperature conditions. The identification of key factors affecting early seedling performance provides practical guidelines for improving seedling production and selection criteria to accelerate pistachio breeding programs.