Size-controlling Interstocks Affect Growth Vigour by Downregulating Photosynthesis in Eight-Year-old ‘red Fuji’ Apple Trees

To understand how interstocks reduce vigour and positively influence yield efficiency, we investigated 'Red Fuji' apple (Malus domestica) scions that were grafted onto five different interstocks. Morphological and physiological parameters, such as growth vigour, gas exchange, leaf area index, soil-plant analysis development value, 100 leaf weight, dry biomass, yield efficiency and fruit quality were examined during their eighth growing season in 2018. Compared to semi-dwarf apple trees, dwarf apple trees had lower growth vigour, photosynthetic capacity root-shoot ratio, and yield per tree, but had a greater short/medium shoot ratio, higher water use efficiency, yield efficiency and better fruit quality especially scions grafted onto the interstock Mark The downregulated photosynthetic capacity induced by dwarfing interstocks could be primarily ascribed to a reduced SPAD value (chlorophyll content or leaf nitrogen). Throughout the experiment, a strong positive linear correlation was observed between the photosynthetic rate and total dry biomass. The distribution of dry biomass in the aboveground and belowground organs further indicates that the differing growth vigour and biomass among the five interstocks were induced by the variation of the accumulation of photoassimilates and translocation. This may have led to greater carbohydrate availability in scions.