Predicting apple tree (Malus × domestica Borkh.) canopy architecture: phytohormone balance in juvenile hybrids.

Apple tree (Malus × domestica Borkh.) is one of the most widespread and economically important fruit trees. Productivity and economic effect of apple orchards depend on many strongly related factors, one of them being tree canopy architecture, which determines fruit bearing and demand for pruning. Main apple canopy architecture topics are related to application of growth regulators, fertilizers, studies of shoot development and pruning, and environmental influence while physiologic aspects are studied less. Phytohormones play a major role in controlling many physiological processes of plant growth and development. Different amounts of phytohormones are found in the shoots of apple trees depending on their canopy architecture. However, information about phytohormones and their ratio in juvenile orchard plants is insufficient. Our goal was to identify phytohormones related to apple canopy architecture and to evaluate their usage as biochemical markers in predicting future canopy ideotype of apple seedlings in the first year of growth. It was established that large amount of auxin and high auxin to zeatin ratio are specific to columnar apple trees and they can be used as biochemical markers in juvenile phase. These amounts and ratios are similar in juvenile and cropping columnar apple trees, so phytohormone amount and ratio is independent of tree development stage. It is possible to select columnar apple hybrids in the first year of growth, thus reducing breeding expenses.