Modification of Fruit Quality and Leaf Mineral Composition of ‘Nagafu No.2’ Apple Grafted onto Four Dwarfing Interstocks

The application of dwarfing interstocks to establish high-density apple orchards in cold and windy areas with barren soil and high altitude has become a new apple cultivation model in many countries. The physicochemical parameters of Fuji apple cv. ‘Nagafu No.2’ grafted onto four different interstocks SH.6, SH.38, SC.1, and M.26 were investigated to clarify how different interstock–scion combinations affect fruit quality. Fruits on M.26 had higher fruit weight, skin color, total soluble solids (TSS), anthocyanin, and sugar/acid ratio than those grafted on other interstocks. Different sugars and hormones responded differently to interstocks, which may be related to the interactions between interstocks and scion. Seventy-one volatile compounds were identified in the apple headspace by gas chromatography–mass spectrometry (GC–MS), mainly including esters, aldehydes, alcohols, hydrocarbons, and acids. Notably, there were 20 volatiles with odor activity values (OAVs) greater than 1 that contributed significantly to apple flavor. Additionally, the absorption capacities of M.26 and SC.1 interstocks to most nutrient elements were stronger than that of SH interstocks. This study demonstrated that interstocks could affect the metabolism and transportation of sugars, phytohormones, and other physicochemical indexes to determine apple quality. Taken together, this study elucidates the effects of different dwarfing interstocks on fruit quality and provides a basis for future apple interstock selection.