MODIFICATION OF CANOPY ARCHITECTURE IMPOSED BY ARTIFICIAL SPUR EXTINCTION PROMOTES RELIABLE CROPPING BEHAVIOUR AND ENHANCES FRUIT QUALITY OF 'SCILATE' APPLE TREES

Abstract

Young trees of the recently commercialised apple ‘Scilate’ (EnvyTM) appear precocious, have excessive fruit set, and produce naturally large fruit. Without precise control of cropping, these characteristics could limit vegetative growth of young trees and may promote biennial bearing. Thus, we applied artificial spur extinction (ASE) in spring to reduce floral bud numbers of three-year-old ‘Scilate’ trees from 18 (unmodified) to 5 floral buds/cm2 branch cross-sectional area (BCA). In the following winter, densities (number/cm2 BCA) of spurs (S) and short to medium length annual shoots (T) on unmodified branch units were 8.2 and 2.4 (S+T=10.6), respectively. In contrast, ASE lowered (P < 0.001) spur density (S=4.5) but increased (P < 0.01) that of annual shoots (T=3.6; S+T=8.1). In the subsequent spring, densities of floral spurs (FS) and floral terminal buds (FT) on unmodified branch units were 2.3 and 1.6 (FS+FT=3.9), respectively. ASE had a similar density of floral spurs (FS=3.2), but twice the density (P < 0.001) of floral terminal buds (FT=3.1; FS+FT=6.3). Gross yields for unmodified trees in the third, fourth, and fifth years from planting were 29, 26, and 50 kg/tree, respectively. For ASE, corresponding gross yields were 25, 30, and 48 kg/tree. In addition to preventing a biennial pattern of bearing, ASE increased red blush coverage around the surface of the fruit skin by 6-7%, enabled a greater proportion of crop to be colour-picked in the first and/or second commercial harvests, and increased fruit dry matter content. These benefits of ASE were not explained by treatment differences in crop load, and may have resulted from reduced spur density improving the illumination of canopy and fruit.