ENDOGENOUS GROWTH REGULATORS AND ROOTSTOCK/SCION INTERACTIONS IN APPLE AND CHERRY TREES

With apple, studies with isolated shoots suggest that the cytokinins which are transported from rootstock to scion in the xylem sap have a major control in shoot growth and any effect of rootstock or interstock on these growth regulators is likely to be of greater significance than effects on the phloridzin, gibberellins or ABA of the sap. The graft unions of dwarfing rootstocks or interstocks with the scion appear to deplete the solute of the xylem sap including the cytokinins.

With cherry, studies with the hybrid cherry rootstock 15 (Prunus avium x P. pseudocerasus) indicate that it is very dwarfing as a scion but very invigorating as a rootstock. As an interstock it has no effect unless allowed to produce some small shoots and then it dwarfs by 20–30%. Possibly this is the result of growth inhibitor production by the elongating shoots. Other hybrid cherry rootstocks such as Cherry 50 and Cob may be similar to Cherry 15.

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