Rootstock effects on growth, yield and nut quality of pistachio (Pistacia vera l.) under semi-arid conditions of Ardakan (Iran)

Rootstock selection is a major determinant of pistachio ( Pistacia vera L.) productivity and physiological performance under arid and semi-arid conditions. In this study, the agronomic, physiological, and nut quality responses of the pistachio cultivar ‘Ahmad Aghaie’ grafted onto three rootstocks ‘Badami Ardakan’, ‘Hassan Abbasi’, and UCB-1 were evaluated under semi-arid conditions in Ardakan, central Iran. Eleven-year-old trees were assessed for 33 morpho-physiological, yield, and nut quality traits. Results showed rootstock significantly affected most measured traits. ‘Badami Ardakan’ produced the highest yield (3.6 kg tree⁻¹) and yield efficiency (10.18 g cm⁻²), along with the largest canopy volume (1.37 m³) and superior kernel dimensions. ‘Hassan Abbasi’ exhibited the greatest TCSA (0.60 cm²), highest nut dehiscence rate (88%), lowest blankness (30%), and the highest chlorophyll a (19.46 μg g⁻¹ FW), total chlorophyll (28.07 μg g⁻¹ FW), and carotenoid content (11.80 μg g⁻¹ FW). In contrast, UCB-1 showed reduced vegetative vigor, smaller nut and kernel size, higher blankness (40.66%), and markedly lower yield (0.75 kg tree⁻¹; 2.10 g cm⁻²). PCA clearly separated UCB-1 from the two local rootstocks, which clustered with traits related to yield, kernel development, and photosynthetic performance. HCA further confirmed distinct phenotypic groupings, highlighting coordinated responses among vegetative, reproductive, and physiological traits. In general, the results demonstrated that locally adapted P. vera rootstocks outperform UCB-1 under semi-arid conditions and emphasized the importance of region-specific rootstock selection for sustainable pistachio production.