Phenological and Pomological Evaluation Reveals High Diversity among Walnut Populations in Southwestern Iran

High genetic diversity guarantees success in a breeding program. Therefore, it is important to study the genetic diversity in plant populations. Because Iran considers as one of the primary walnut origin centers, this study was conducted to evaluate the genetic diversity of the walnut population in the Bavanat region in Southwestern Iran during the 2010-2015 growing season. For this purpose, 349 seed-originated walnut trees from seven different regions of Bavanat were pre-selected based on the local information. After primary evaluation, 92 walnut genotypes were selected for further studies. The phenological and pomological characteristics of the genotypes were evaluated based on IPGRI descriptor. The results revealed high genetic diversity in the studied germplasm in terms of important horticultural traits, especially nut and kernel weight, kernel percentage, nut size, shell thickness, lateral bearing, leafing date, and harvest date. The nut weight, kernel percentage, kernel weight, and shell thickness varied between 6.75-16.33 g, 40.15-67.22%, 3.30-8.15 g, and 0.58-2.30 mm, respectively. Cluster analysis classified the studied genotypes into six main groups. Furthermore, correlations among some horticultural traits indicated that kernel weight, nut weight, difficulty of removal of kernel halves, and shell thickness are main traits in determining kernel percentage. Also, lateral bearing, leafing date, nut weight, and nut size determine the final yield of walnut trees. In conclusion, high biodiversity in the walnut population of Bavanat region provides unique plant genetic resources for walnut genetic improvement programs to achieve desirable commercial cultivars and rootstocks.