Selecting the superior late-leafing genotypes of Persian walnut (Juglans regia L.) using morphological and pomological evaluations

BACKGROUND: Late-spring frost is one of the major factors limiting and reducing yield of Persian walnut (Juglans regia L.) in temperate regions, including Iran. Therefore, in the present study, seedling-originated genotypes of walnut were investigated to identify late-leafing genotypes with high-quality kernels for direct cultivation in orchards or as parents in breeding programs. In the first step, the variation of the selected trees was investigated in terms of traits related to phenology, vegetation, and fruit. In the second step, late-leafing trees were identified and their traits related to kernel quality were investigated to identify superior genotypes. RESULTS: Strong variabilities were exhibited among the studied genotypes based on the traits recorded. The genotypes showed high variation based on dates of leafing, full male flowering date, and full female flowering date, including very early, early, moderate, and late. After recording the leafing date, 21 late-leaf genotypes were identified and evaluated to select the superiors among them in terms of kernel quantity and quality. Among them, the values of nut-related traits ranged as follows: nut length: 30.12–49.74 mm, nut width: 29.31–37.17 mm, nut weight: 8.77–16.47 g, and shell thickness: 1.15–2.25 mm. The values of kernel-related traits ranged as follows: kernel length: 22.35–35.73 mm, kernel width: 21.79–29.03 mm, kernel weight: 3.22–8.17 g, and kernel percentage: 35.08–53.95%. CONCLUSIONS: According to the ideal values and situations of commercial characteristics of walnut, twelve promising late-leafing genotypes (No. 9, 13, 32, 33, 72, 77, 78, 82, 83, 86, 92, and 98) were identified and are recommended for cultivation in orchards.