Model-assisted evaluation of crop load effects on stem diameter variations and fruit growth in peach

Stem diameter (Dstem) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two Dstem derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however, influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of
crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit
growth stages.