Effects of different crop loads on growth, physiological indexes, and fruit quality of Luli apple trees

To achieve good apple yields and high fruit quality, effective management of crop load is essential. This study was conducted over two consecutive years (2024 and 2025) to investigate the effects of varying crop loads on growth, physiological status, endogenous hormone levels, and fruit quality of the mid-ripening apple cultivar 'Luli'. Using 5-year-old Luli trees subjected to five crop load treatments, we found that moderate crop load (T3) optimally balanced vegetative growth and fruit development. Excessive load significantly inhibited tree growth, photosynthetic efficiency, carbohydrate accumulation, and fruit quality, while low load improved fruit quality and some growth parameters but reduced overall yield. Photosynthetic parameters such as total chlorophyll content, maximum photochemical efficiency, net photosynthesis rate, and stomatal conductance were highest under the T3 treatment, correlating positively with fruit quality indicators. Hormonal analysis showed that T3 maintained favorable hormone levels that support fruit development. Fruit quality metrics including fruit weight, size, soluble solid levels, and color were superior in T3, which also produced the higher proportion of premium-grade fruits. These findings provide a theoretical foundation for sustainable orchard practices in mid-ripening cultivars.