Morphometric traits and iPBS based molecular characterizations of walnut (Juglans regia L.) genotypes

In this study, walnut genotypes that were selected during two growing seasons among thousands of seedlings were analyzed in terms of detailed morphometric, phenological, and chemical traits. A multivariate analysis was conducted with valuable traits for breeding and selection such as morphometric traits, chemical composition, and phenological characteristics. Also, genotypes were characterized by a retrotransposon-based iPBS marker system. The correlation analysis showed significant positive and negative correlations between agro-morphological characters. The principal component analysis explained 71.44% of the total variance into five main components. Principal component and hierarchical cluster analysis divided genotypes into three groups and identified subgroups based on both agro-morphological characters and iPBS marker systems. A high level of polymorphism ratio was observed for tested markers. Mantel's test demonstrated relatively low correlations between molecular and morphological treats (r = 0.04). The genetic similarities among all individuals ranged from 0.39 (between 018 and 015 or 045 genotypes) to 0.98 (between 090 and 094 genotypes) with a mean similarity of 0.67. Remarkable phenotypic and molecular variations were observed among the genotypes. The features of some investigated genotypes were above the acceptable thresholds for walnut selection in breeding programs, and our study indicated that iPBS markers can be beneficial in walnut breeding programs, allowing the evaluation of the genetic relationship between genotypes, helping to differentiate and select the best genotypes to improve agronomic properties.