Superior spring frost resistant walnut (Juglans regia L.) genotypes identified among mature seedling origin trees

Abstract

In many areas, Persian walnut (Juglans regia L.) production is limited by the spring frost, which can damage sensitive tissues. The current investigation was carried out to select the spring frost resistant genotypes with high values of kernel quality and quantity among the mature seedling origin trees. In the year of study, early and moderate leafing and flowering genotypes in the studied regions did not produce fruit due to spring frost damages on flowers and thus were excluded from the study. Finally, by several visits to the orchards in the selected sites, 67 mature seedling genotypes were found to be late-flowering which have not been exposed to frost and thus were selected for final pomological evaluations. The studied genotypes showed significant differences for all the measured pomological traits. The range of nut weight varied from 7.53 to 16.91 g, while the range of kernel weight varied from 3.17 to 8.23 g. The range of kernel percentage varied from 39.44–68.14%. Kernel percentage was positively and significantly correlated with nut diameter (r = 0.27), kernel width (r = 0.32), and kernel weight (r = 0.53), and also negatively correlated with shell thickness (r = −0.41). Based on ideal values of the main traits related to nut and kernel in walnut, 14 genotypes were superior and could be selected for cultivation. Moreover, they might be used as parents to improve the cultivated ones in the breeding programs.