Phenotypic Diversity and Selection of Superior Pistachio (Pistacia vera L.) Genotypes from Kyrgyzstan Using Multivariate Approaches

Pistachio (Pistacia vera L.) is an economically important nut crop facing challenges including limited genetic diversity in commercial cultivars, climate change-induced insufficient chilling, and quality deficiencies such as low splitting ratios and blank nuts. This study evaluated 93 pistachio genotypes collected from Kyrgyzstan to identify superior genetic material for breeding programs through comprehensive pomological characterization, phenological assessment, and multivariate analysis. Nut dimensions ranged from 14.47 to 19.41 mm in length, with size measurements spanning 1.03 to 2.43 cm². Kernel weight averaged 0.33 g (0.26-0.48 g) and kernel ratio ranged from 24.53% to 57.26% (mean 48.11%). Splitting ratio varied widely from 16.14% to 94.49% (mean 69.13%), while 100-nut weight (48.25-97.16 g, mean 66.34 g) demonstrated substantial variability. Thickness measurements ranged from 7.13 to 11.01 mm (mean 8.66 mm) and width spanned 8.21 to 11.82 mm (mean 9.77 mm). Selection index analysis (SI > 0.702) identified 12 superior genotypes (13.04%) exhibiting balanced performance across multiple quality traits, with KT-092 ranking highest (SI = 1.84), followed by KT-089 (SI = 1.60), KT-042 (SI = 1.55), and KT-085 (SI = 1.07). Elite genotypes KT-092 and KT-089 demonstrated very high composite scores with exceptional kernel weights (0.48 g), superior nut sizes (2.43 and 2.27 cm²), thin shell thickness (0.66 mm), and excellent splitting characteristics. Six genotypes (KT-042, KT-085, KT-093, KT-074, KT-090, KT-002) achieved high composite SI scores, while four genotypes (KT-091, KT-033, KT-066, KT-051) displayed moderate performance with specific trait advantages. Phenological observations revealed significant variation in bud development and flowering timing, with bud swelling spanning 14 days (March 18 to April 1, 2025) and flowering duration ranging from 6 to 9 days. Strong positive correlations were observed among dimensional and weight-related traits, while kernel ratio showed independence from nut size, facilitating flexible breeding strategies. The Kyrgyzstan germplasm represents an underexplored genetic resource with substantial phenotypic diversity, offering valuable material for developing climate-resilient cultivars with enhanced kernel quality and superior splitting characteristics.