Effect of Spur Defoliation and Ringing during Bloom on Fruiting, Fruit Mineral Level, and Net Photosynthesis of ‘Golden Delicious’ Apple1

Leaf areas on individual spurs were modified in the pink stage of flower development on ‘Golden Delicious’ apple ( Malus domestica Borkh.), and the effects on fruiting, mineral content, and net photosynthesis (Pn), of leaves on those spurs determined. Removal of a 3mm-ring of bark from the spur increased initial fruit set, determined 1 week after petal fall, compared to normal spurs. The combination of ringing and removal of all leaves resulted in a complete loss of fruit. Final fruit set was reduced by any treatment involving ringing, reduction in spur leaf area, or injury to the stigmas. The greatest number and total weight of fruit at harvest were given by undefoliated, unringed spurs where the bourse shoot was allowed to develop. Ringing reduced Pn at petal fall but had no effect later in the season. Presence of the bourse shoot reduced Pn of spur leaves in early June. Spur leaves on fruiting trees had an important localized influence on fruit set, ultimate fruit size, and fruit Ca level of fruit produced on that spur.