Correlation Analysis of Vegetative and Flowering Traits with Yield and Kernel Quality in Walnut (Juglans regia L.)

Understanding the association among vegetative growth, flowering behaviour, yield and kernel quality traits is essential for improving selection efficiency in walnut breeding programmes. The present investigation was conducted during the 2023–2024 growing season at the Walnut Orchard, Faculty of Agriculture, Wadura, SKUAST-K, to evaluate phenotypic correlations among vegetative morphological traits, flowering phenology, yield, and kernel quality attributes in twenty-one walnut (Juglans regia L.) genotypes maintained under uniform orchard management conditions. Vegetative traits such as time of bud break, leaf length, leaf width, leaflet length, leaflet width, and number of leaflets were recorded, along with flowering parameters, yield per tree, nut physical traits, and kernel biochemical characteristics including protein and oil content. Correlation coefficients were computed to assess the magnitude and direction of associations among the studied traits. The results revealed that yield per tree exhibited weak and non-significant associations with most vegetative traits, including bud break (r = −0.17), leaf length (r = 0.06), and leaflet length (r = 0.04), indicating a limited direct influence of vegetative morphology on productivity. Several vegetative traits showed significant negative correlations with nut size parameters, particularly leaf length and leaf width with nut diameter at suture and cheek. Leaflet width, however, exhibited a significant positive correlation with kernel protein content (r = 0.44), suggesting its role in influencing kernel biochemical quality. Flowering phenology demonstrated stronger and significant positive associations with kernel recovery percentage, notably first male bloom (r = 0.45), peak male bloom (r = 0.46), last male bloom (r = 0.46), and first female bloom (r = 0.52). Flowering overlap also showed a positive association with yield, highlighting the importance of reproductive synchrony in walnut. In conclusion, flowering behaviour was found to be more closely associated with kernel recovery and yield stability than vegetative growth traits. The study suggests that flowering-related traits and selected vegetative parameters influencing kernel quality may serve as reliable indirect selection criteria in walnut improvement programmes. Future research should focus on validating these associations across environments and integrating phenological and biochemical traits with molecular markers to enhance selection efficiency in walnut breeding.