Modeling size-controlling rootstock effects on peach tree growth and development using L-PEACH-h

Vigorous peach scion cultivars, growing on graft-compatible rootstocks, exhibit differing amounts of vegetative growth, depending on the rootstock used. Recent research on the physiology of peach size-controlling rootstocks has indicated that the primary factor, that limits the vegetative growth, appears to be the hydraulic conductance characteristics of the rootstocks. There is good evidence that the size-controlling rootstocks have smaller mean xylem vessel diameters that lead to decreased axial hydraulic conductance, and therefore, to slightly decreased water potentials in the scion stems. Previous research has also documented direct (relative stem extension growth rates) and indirect (decreased leaf photosynthesis rates) linkages between stem water potentials and shoot growth rates. In the past year, a functional-structural plant model, for simulating peach tree growth and physiology, L-PEACH, was modified to simulate, on an hourly basis, the uptake, transport and transpiration of water, simultaneously with the carbohydrate assimilation and distribution. Thus, the new model, L-PEACH-h, can estimate stem water potentials for each hour and for each node in the tree, and use these water potential values to modify simulated shoot growth and physiological functioning of the leaves. In this presentation, we demonstrate how these new developments allow simulation of cumulative effects of size-controlling rootstocks on peach tree growth.