Trade-off between trunk radial growth and fruit yield and its relationship to xylem traits in composite apple and pear trees

The project aims to disentangle carbon allocation priorities between trunk radial growth and fruit yield (G-Y trade-off) and elucidate how the strength of the G Y trade-off relates to xylem structural and functional traits. Our studies will take advantage of 41 composite tree variants of domestic apple and European pear that differ in radial growth vigour and susceptibility to alternate bearing. To test for the existence of the G-Y trade-off, we will use long-term data on fruit yield and ring width increments. In a subset of contrasting trees, we will analyse hydraulic and storage functions of xylem as well as its construction costs to elucidate links with growth and yield parameters. The dynamics of radial growth and non-structural carbohydrates (NSC) will be studied in trees with experimentally manipulated fruit loads to directly evaluate how strongly fruit production competes with radial grow and how much it draws on NSC reserves. The results will advance fundamental understanding of carbon allocation and xylem functioning in trees and will be valuable for horticultural praxis.