Optimum Corp Load and Dry Weight Partitioning in ‘Fuji’/M.26 Apple Trees

Abstract

Normally to heavily cropped ‘Fuji’/M.26 apple trees were compared to examine the influence of corp loads on growth, yield, fruit characteristics and flower bud formation during 1986 and 1987. High correlation coefficients were observed between the leaf-fruit ratio and mean fruit weight, shoot weight, flower bud formation and yield. The results of the studies indicated that yeild, mean fruit weight, brix of fruit, current shoot weight and flower bud formation were very sensitive to crop load. The optimum crop load of ‘Fuji’/M.26 apple trees was estimated to occur at 50 to 60 leaves per fruit.
Nine-year-old normally and heavily cropped ‘Fuji’/M.26 apple trees were used during the 1987 growing season to determine the distribution of leaf photosythate in the trees on a dry weight basis. Five trees in each of the normal and heavy-crop load treatments were fractioned into the trunk, branches, new shoots, leaves, fruit, and roots. Total dry matter accumulation per tree was essentially the same in heavily or normally cropped trees, but the distribution of the dry matter resulted in significant differences between the two treatments.
The distribution of the accumulated dry matter was 73% in fruit, 9% in leaves, 15% in wood and 4% in roots in the heavily cropped trees. In the normally cropped trees, the proportions of dry matter in fruit was 49%; the other sections were approximately equal with 9 to 12% each. The heavily cropped trees produced 137% more total dry matter per unit weight of leaves than normally cropped trees.