Influence of partial spur leaves removal on fruitlet shedding, fruit quality and shoot growth in apple trees as a basis for mechanical thinning

Knowledge of the physiology of natural fruitlet shedding is especially important to insure thinning efficiency in apple production. The effect of partial spur leaf removal on shedding, as well as on fruit quality and bourse shoot growth, was investigated. Removing spur leaves increased shedding, while there was no effect of partial leaf removal on mature fruit quality in terms of weight, firmness and sum of sugars, detected by HPLC-RI and resulted in lower contents of citric, fumaric and shikimic acids, detected by HPLC-UV. Growth of bourse shoots was poorer in treatments with leaf removal. To summarize, a decreased number of spur leaves caused more intensive fruitlet abscission and poorer bourse shoot growth but had no negative influence on fruit size. These results show the potential use of decreasing spur leaf area to stimulate more intensive natural shedding to support fruitlet thinning, which could be used in combination with prospective mechanical thinning.