Introduction
Thomson navel orange occupies the largest cultivation area among citrus species in eastern Mazandaran owing to its high adaptability and yield potential. In northern regions, trees are commonly trained to a spherical canopy form. However, this structure restricts light penetration into the inner canopy due to shading by upper branches and leaves, thereby confining flowering and fruiting largely to the shape of canopy. The present study aimed to enhance light penetration into the inner canopy through pruning and to assess its effects on flowering and selected quantitative and qualitative traits of Thomson navel orange fruit.
Materials and Methods
The experiment was conducted during the 2019–2020 growing season in a commercial orchard located in the Mushk-Abad area of Jouybar. A randomized complete block design with seven treatments and three replications was employed. Light intensity within the canopy under different pruning treatments was measured at 09:00, 12:00, and 15:00. Additionally, the number of flowers, number of leafy inflorescences, and fruit traits including number, length, diameter, volume, and color were recorded.
Results and Discussion
Pruning treatments significantly affected light distribution within the canopy. The highest light penetration into the inner canopy was recorded in pruning type F (open-center pruning combined with removal of branches from the east, west, and south sides), with a mean of 453 µmol m⁻² s⁻¹, followed by type E (open-center pruning with removal from the west and south sides) at 365 µmol m⁻² s⁻¹. The lowest value (12.7 µmol m⁻².s⁻¹) was observed in the control (type A: unpruned spherical canopy). The highest mean number of flowers (270) was obtained in pruning type F, whereas the lowest values (216–218 flowers) were observed in treatments A and G (open-center pruning with removal from the south side). A similar trend was observed for the number of leafy inflorescences, with the highest values recorded in type F. This treatment also exerted a positive effect on fruit traits, including length, weight, and volume. Fruit set percentage was highest in type F (15.4%) and lowest in type B (open-center pruning) at 3.2%. The greatest number of fruits was observed in type F (14 fruits), followed by type E (12.33 fruits), whereas the lowest values were recorded in the control (type A) and type B treatments. Overall, pruning type F, which maximized light penetration into the canopy, enhanced flowering and fruiting within the inner canopy and improved both quantitative and qualitative fruit characteristics.
Conclusion
Enhanced light availability within the inner canopy promotes flower formation, development of leafy inflorescences, and fruit set in Thomson navel orange trees. Moreover, improved light distribution positively influences fruit physical attributes, including length, diameter, weight, and color. Therefore, the adoption of appropriate pruning strategies—particularly pruning type F—is recommended to achieve optimal yield and superior fruit quality.