Identification of superior walnut (Juglans regia) genotypes with late leafing and high kernel quality in Iran

• As a result of the pre-selection according to leafing date, 61 trees were selected that were late leafing.
• The variation was observed for traits related to nut and kernel.
• Nut dimensions and weight were in significant positive correlation with kernel weight.
• Cluster and principal component analyses confirmed considerable diversity in the studied germplasm.

In many areas of Iran, walnut production is limited by spring frosts that can damage the sensitive non-dormant tissues. The present study was carried out within a seedling population in order to select superior walnut genotypes in term of consistent late leafing time and high kernel quality. As a result of the pre-selection according to leafing date, 61 trees were selected that were late leafing. Then, the selected trees were further evaluated according to nut and kernel characteristics. The variation was observed for traits related to nut and kernel. Variability found in nut weight was between 7.70 and 22.33 g, in kernel weight between 2.30 and 8.53 g, and in kernel percentage between 24.66 and 62.18%. 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 confirmed considerable diversity in the studied germplasm. All of the 61 studied genotypes were late leafing and could be useful as a parent to improve leafing and flowering season of cultivars. Furthermore, genotypes 6, 14, 15, 17, 34, 37, 38, 40, 45, 47, 53, 54, 56 and 57 were superior in terms of consistent high kernel percentages, large nut, shell softness, large kernel, light kernel color, ease of kernel removing from nuts, and none blank nut percentage and can be singled out for cultivation.