Characterization and selection of walnut (Juglans regia L.) genotypes from seedling origin trees

Abstract

The Persian walnut is one of the most important horticultural crops grown in Iran. In the current study, a walnut germplasm from the six regions of Fars, located in the southwestern part of Iran, was evaluated to determine the variability and to identify promising types. A total of 232 genotypes were evaluated using 30 phenological and pomological characteristics. Considerable genetic variation in the measured traits was found in native trees which were of seedling origin. Variability found in nut weight was between 8.00 and 23.00 g, in kernel weight between 4.00 and 14.00 g, in shell thickness between 0.10 and 3.00 mm, and in kernel percentage between 40.00 and 72.22 %. Also, bud breaking, flowering, and nut maturity times showed wide variation among genotypes. Results from simple correlation analysis showed significant positive and negative correlations for certain important characteristics. Nut dimensions and weight were in significant positive correlation with kernel weight. The kernel percentage was in positive correlation with kernel weight, kernel filled, and kernel plumpness and in negative correlation with shell thickness. Cluster and principal component analyses showed a considerable diversity in the studied germplasm. The results indicated that most of genotypes were suitable in terms of consistent leafing date, lateral bearing, kernel weight, kernel percentage, and kernel color which can be singled out for cultivation. Furthermore, they could be useful as a parent to be crossed to generate appropriate populations or improve cultivars. These data collectively demonstrated large phenotypic diversity among the selected genotypes that can be considered as a valuable gene pool for breeding programs.