Annual shoot growth on apple trees with variable canopy leaf area and crop load in response to LiDAR scanned leaf area to fruit ratio

Abstract

In tree fruit crops, the crop load is one factor that has an influence on the vegetative growth of the trees. However, since trees vary in leaf area and associated fruit bearing capacity, the number of fruit per tree alone is not sufficient to predict their vegetative growth. In the present study, it was investigated whether the leaf area to fruit ratio of trees variable in size and crop load, measured automatically with a LiDAR laser scanner, have an influence on growth properties of the annual shoots. Canopy leaf area, the number of fruit per tree and the leaf area to fruit ratio of apple trees from two commercial apple orchards of the cultivar 'Gala' grown on sandy soils were scanned with a LiDAR laser scanner over a two-year period (n=12 trees per orchard and year). Additionally, the amount of carbon partitioned to fruit and annual shoot growth was quantified for each tree in both years (n=36). No correlation between the number of fruit per tree and the canopy leaf area alone to the amount of carbon partitioned to annual shoot growth was found in both orchards. However, the carbon partitioned to fruit correlated to the leaf area to fruit ratio, while the amount of carbon partitioned to the annual shoot growth was only correlated to the leaf area to fruit ratio in the young orchard. The inter-tree variability in shoot properties has been described. Nevertheless, it was found that the leaf area to fruit ratio is a weak indicator for shoot properties in apple trees, especially in the mature orchards.