Effect of Dwarfing Interstocks on Xylem Sap Composition in Apple Trees: Effect on Nitrogen, Potassium, Phosphorus, Calcium and Magnesium Content

Abstract

This paper concerns nutrient concentrations in xylem sap collected from above and below M.8, M.9, M.26 and M.7 dwarfing interstocks. The sap flowing from above an interstock had lower concentrations of nutrients than that from the rootstock levels and these differences increased with the dwarfing effect of the interstock. There were indications that nutrient concentrations were enhanced below interstocks but were reduced in the sap flowing from the interstocks into the scions. Generally these reductions were greater the more dwarfing the effect of the interstock. Analyses of sap from above, mid-way along and below interstocks indicated that the changes in content were produced in, or close to, the graft union between scion and interstock.