Breeding of Persian walnut: Aiming to introduce late-leafing and early-harvesting varieties by targeted hybridization

Due to climate change, late-spring frost is considered as a main limiting factor for walnut production. The sustainable strategy to alleviate this challenge is to use late-leafing cultivars with desirable nut characteristics. In order to achieve late-leafing and early-harvesting cultivars, this breeding program including 3635 controlled crosses between 'Persia', 'Caspian', 'Chandler', 'Pedro' as female parents and 'Franquette', 'Lara' and superior genotype 35T as male parents was conducted during 2018-2019. The results showed that there is a significant difference between the cross combinations in terms of fruit set and pollen tube growth. So that, the highest final fruit set was observed in the cross female Chandler x male 35T (67.90%). Also, the fruit growth period of different cross combinations varied between 134 and 157 days. The nut weight, kernel weight and kernel percentage of the obtained progenies ranged between 8.38-12.13 g, 4.19-8.24 g and 41.50-68.67%, respectively. The highest kernel percentage was observed in ?Persia x ?35T cross combination (68%). The hybrid seeds were planted in pots under greenhouse condition in the first year, and after initial growth, one-year-old seedlings were transferred to the nursery. Evaluation of the studied seedlings in 2020 showed that there was a significant variation (45 days) between seedlings in terms of leafing date. The early-and late-leafing genotypes were obtained when 35T and 'Franquette' used as male parents, respectively. Although, the studied seedlings have not yet reached the maturity phase for evaluating harvest date, but due to the great variation in leafing date, we hope to reach late leafing and early-harvesting genotypes with desirable nut traits in the continuation of this breeding program.