Phenological characteristics of walnut (Juglans regia L.) genotypes under environmental conditions of Karaj in Iran

Walnut (Juglans regia L.) is one of the most important horticultural crops grown in Iran. To characterize the phenology of walnut genotypes in different seasons and its relationship with climatic conditions, this study was carried out in temperate fruits research center of Horticultural Science Research Institute, Karaj, Iran. The phenological characteristics of 39 selected superior walnut genotypes were compared with Chandler, Jamal and Rond de Montignac cultivars during 2012-18. The results showed that the overall average leafing dates of genotypes varied from March 15-29 over seasons. ‘Z16’ had the earliest leafing date (March 13) together with ‘Kr95’and high variation (24 and 25 days, respectively). Latest leafing date (April 13) and least variation (four days over seasons) belonged to ‘Ronde de Montignac’. The average leafing dates in ‘Chandler’, ‘88-1, ‘88-2’ were in April 6-8. The average pollen shedding, in different seasons, started in genotypes from March 29 to April 12. While the average of pistillate flowers receptivity varied from April 2 to April 11. The effect of season was not significant on nut ripening. The overall average fruit ripening was on August 24-25 in different seasons. However, the ripening dates for walnut genotypes varied from August 15 in ‘Kr111’ to September 16 in ‘Chandler’. The temperature of March showed to have a crucial effect on bud break, catkin development, pollen shedding, and pistillate flowers development and receptivity period. Leafing date showed to be more affected by season in comparison to other phenological characteristics. The leafing dates varied 5.5 and 2.8 days, with 1 °C increase in average temperature, in early and late leafing genotypes, respectively.