Effect of Notching, 6-Benzyladenine, and 6-Benzyladenine plus Gibberellin A4 + A7 on Budbreak and Shoot Development from Paradormant Buds on the Leader of Young Apple Trees

Notching is a technique to stimulate shoot growth from paradormant buds with the long-term objective of increasing the cropping potential of fruit trees by developing new fruiting scaffolds. Notching is not commonly practiced by apple (Malus ·domestica) growers in the southeastern United States because results can be inconsistent; notched buds frequently develop into weak spurs producing a few leaves rather than strong extension shoot growth. Therefore, a study was initiated to investigate the potential of 6-benzyladenine (6-BA) to enhance the shoot growth response from notched buds on 2or 3-year-old wood. Notching paradormant buds on the leader of young ‘Granny Smith’/‘M.26 EMLA’ (‘M.26’) trees at the pink bud stage resulted in new growth developing on 59% of notched buds; however, fewer than 4% of these extended beyond 1.0 cm in length. Spray application of a solution of 1.5 g L 6BA into the notch increased budbreak to 95% and the proportion of new growth that developed into shoots to 89%, with a mean new shoot length of 7.9 cm. In a timing study on ‘Granny Smith’/‘M.26’, the optimum budbreak and shoot growth responses to notching plus 6-BA treatment were observed between budbreak and 2 weeks after budbreak. Notching paradormant buds on the leader of ‘Fuji’/‘M.9 T337’ (‘M.9’) trees increased budbreak, with 83% of the new growth developing into extension shoots. Spray application of 0.75 g L 6-BA into the notch did not increase budbreak or extension growth of ‘Fuji’/‘M.9’ compared with notching alone. Spray application of a solution of 6-BA directly into a notch made above a paradormant bud may greatly enhance budbreak and shoot extension responses in cultivars or situations where a poor response to notching alone is expected.