Summer pruning in apple trees is an advisable cultural practice that promotes bud differentiation and improves fruit quality: a literature review

Apples (Malus domestica) are among the most widely cultivated and economically valuable fruit tree crops worldwide. Summer pruning, encompassing thinning, branch bending, and ring wounding, is a method of regulating apple production and is important to fruit tree growth. Timely and appropriate application of this measure can control the vigorous growth of new shoots, promoting the differentiation of flower buds, enhancing early fruiting and yield of young trees, improving the ventilation and light conditions of trees, and reducing the occurrence of pests and diseases, thereby achieving superior fruit quality. However, excessive pruning negatively affects the tree's strength, yield, and fruit quality. In this review, we concisely describe the physiological basis of summer pruning, the main manual pruning methods, the latest robotic pruning technologies, and their specific impacts on fruit quality and yield. We also analyze the main problems in current production, emphasizing the importance of robotic pruning as an important management measure for future large-scale and intelligent development of the apple industry. This information is beneficial to fruit tree researchers and growers and provides a scientific reference for apple production.