Phenotypic diversity of walnut genotypes in Gölköy district (Ordu, Türkiye)

In this study, fruits harvested from 34 wild walnut genotypes (Juglans regia L.) found in nature in Gölköy district (Ordu, Turkey) with larger fruits were evaluated. The main objectives of the study were to compare walnut genotypes based on phenotypic variation based on pomological traits using descriptive, univariate (ANOVA), multivariate (PCA and HCA), and correlation statistical approaches. Fruit weight, fruit width, fruit length, fruit thickness, fruit shape index, fruit roundness index, rind thickness, kernel weight, kernel ratio, and firm-to-firm kernel ratio were investigated. Fruit weight with shell varied between 6.89 and 12.34 g, rind thickness between 1.26 and 1.96 mm, kernel weight between 3.08 and 5.97 g, and kernel ratio between 40.73% and 59.30%. Among the parameters examined, the highest coefficient of variation in the population was observed for kernel weight (23.22%), and the lowest for plump-to-firm kernel ratio (4.93%). Analysis of variance revealed significant variability in nut and kernel characteristics, except for the plump-to-firm kernel ratio. Correlation analysis revealed a high level of positive correlation between fruit weight and kernel weight (0.835***), fruit width (0.820***), fruit thickness (0.767***) and fruit length (0.737***), while the highest negative correlation (-0.993***) was determined between fruit shape index and fruit roundness index. Principal component analysis (PCA) determined that 84.79% of the total variance was explained by the first three components. The first principal component accounted for 42.39% of the total variation, and it was mainly defined by nut weight, nut width, nut length, nut thickness, nut shape index, shell thickness and kernel weight. This suggests that this component primarily reflects pomological traits related to nut size. According to the results of hierarchical cluster analysis (HCA), the genotypes were divided into four main groups. These clusters showed significant differences in fruit traits. It can be said that all the data obtained in the study provides a rich data set for characterizing variation among walnut genotypes and a basis for selection breeding studies. In conclusion, nut weight, nut length and kernel weight can be recommended as basic variables in selection breeding programs.