Rootstock Effect on Stem Water Potential Gradients in cv. 'Armking' Nectarine Trees

The effects of rootstock vigour on scion xylem hydraulic conductivity were studied on potted trees of cv. ‘Armking’ nectarine grafted onto GF677 (vigorous) and MrS 2/5 (low-vigour) rootstocks. Water potential gradients of non-transpiring leaves were measured at three levels of the stem starting at 10 cm above the graft-point. Transpiration rates were estimated by weighing. Two sets of measurements were taken on the same trees, at two different transpiration-rate levels obtained by imposing a different level of evaporative demand. Measurements were taken after allowing transpiration to reach a steady-state (20 minutes after any environmental perturbation). Trees grafted onto the low-vigour rootstock (MrS 2/5) showed the lowest water potential at all levels along the stem and the lowest hydraulic conductivity along the stem, about half the values observed on GF677-grafted and self-rooted trees.