Comparison of Methods to Express Growth, Size, and Productivity of Apple Trees

Abstract

Data from an 18-year rootstock trial with ‘RedChief’ and ‘Red Prince’ strains of ‘Delicious’ and ‘Goldspur’ and ‘Smoothee’ strains of ‘Golden Delicious’ were used to compare multiple ways to express tree productivity and efficiency. Our data confirm the close relationship between trunk cross-sectional area (TCA) and scion weight across a wide range of tree sizes. In addition, our data show that cumulative yield increased at a decreasing rate as tree size increased, whether expressed on the basis of scion weight or TCA. The regression between pruning time and TCA was linear for both strains of both cultivars. The cumulative crop-weight-to-final-scion-weight ratio (C/S ratio) varied widely with rootstock, but much less with cultivar and strain. Trees on M.9 rootstocks had a C/S ratio of about 15, indicating that the average annual production of fruit for each of the 14 fruiting years was equal to the final scion weight. With M.7 and MM.111, the annual yields of fruit were equal to about 50% of the final scion weights. The relative differences in C/S ratio were considerably greater than the cumulative yield efficiencies reported earlier.