Apple shoot growth and cropping responses to root pruning

Abstract

Mature ‘Braeburn’/MM 106, trained on an Ebro trellis, and ‘Cox's Orange Pippin’/MM 106 apple trees, trained on a Lincoln canopy, were mechanically root-pruned along both sides of the row 60 cm from the trunk to a depth of 30 cm at either the dormant stage or at petal fall (‘Braeburn’ only). Root pruning during the dormant phase reduced mean shoot length more than root pruning at petal fall. Treatment at petal fall reduced mean shoot length on the lowest tier of the Ebro trellis only whereas root pruning at the dormant phase reduced mean shoot length on all tiers. Shoot growth rate was reduced during November and December in root-pruned trees. Total length and number of shoots requiring removal during summer pruning was reduced by dormant root pruning whereas light transmission to the lowest tier of the Ebro trellis was increased before summer pruning following dormant root pruning. Root pruning during the dormant phase also increased flowering in the subsequent season. Mean fruit size of ‘Cox's Orange Pippin’ was reduced by dormant root pruning with a more pronounced effect as the crop density (fruit number/cm² trunk cross-sectional area) increased.