The rootstock graft union: a contribution to the hydraulics of the worked fruit tree.

摘要

It has long been suggested that the graft union between a rootstock and a scion may, at least in part, provide a mechanistic explanation of the way dwarfing rootstocks are able to reduce the vegetative growth of a scion. This ability has, with few exceptions, been inferred from observations of the anatomical structure associated with the graft union. Published reports show considerable tissue disorganization, particularly within the xylem. These results suggest that the graft union is a region of low hydraulic conductance, relative to the scion in particular, and this may influence the movement of substances in the xylem such as ions, and water and plant growth regulating hormones. The experiments reported here describe measurements made with a low-pressure flow system designed to determine in situ hydraulic conductance of relatively large stem sections incorporating the graft union (diametric) of two-year-old trees. The experiments described used a range of rootstocks (M.27, M.9 and MM.106) withdiffering capacities to dwarf scions; all of which had been worked with the same scion, i.e. a self-fertile clone of apple cv. Queen Cox. These measurements show that the hydraulic conductance of the graft union varied with the rootstock's capacity to dwarf. These differences in conductance will be discussed and related to their possible involvement in the mechanism(s) by which rootstocks control scion vigour.