Situation and recent trends on cultivation and breeding of Persian walnut in Iran

Persian walnut (Juglans regia L.) is one of the main nut crops in Iran. Walnut together with pistachio and almond have covered more than 800,000 ha (28.5 %) of Iran's orchards. After pistachio, walnut is the second important nut crop in term of production. In recent years, the demand for establishing walnut orchard has significantly increased. Walnut has a long history of cultivation and use and the country considered as one of the main walnut origin and distribution centers in the world. So, it is possible to find some walnut trees with more than 1000-years old in the traditional orchards. The walnut orchards could classify into the traditional and new orchards. In traditional orchards, walnut is usually cultivated on the borders of other fruit tree orchards. In recent years, new walnut orchards have been established using foreign ('Chandler' and 'Fernor') and Iranian commercial cultivars and supeior genotypes. Also, traditional orchards have either been replaced by new ones by top-working. Walnut breeding in Iran is being done by TFRC-HSRI and CEWIT. Germplasm evaluation, hybridization and omics studies are the main walnut breeding strategies. Iran's walnut breeding program initiated in 1983 and led to release of six commercial cultivars including 'Jamal', 'Damavand' (2010), 'Persia', 'Caspian', 'Chaldoran' and 'Alvand' (2019). In addition to cultivar breeding, rootstock program is currently going on, aiming to find appropriate clonal rootstocks.