SIZE-CONTROLLING APPLE ROOTSTOCK EFFECTS ON FINAL TREE DRY WEIGHT AND TOTAL PRODUCTIVE EFFICIENCY

Abstract

After 12 growing seasons, `Starkspur Supreme Delicious' apple trees on 9 rootstock genotypes from very vigorous (MAC 24) to very dwarfing (M.27 EMLA) were divided into branches, trunk, rootstock shank, and roots, and total fresh and dry weights of each component determined. Final tree dry weight (DW) ranged from 2 kg (M.27 EMLA) to 90 kg (MAC 24). Both total top DW and total tree DW (including roots) were closely and linearly related to final trunk cross-sectional area (TCSA). Both total cumulative fruit fresh weight and DW per kg final tree DW increased curvilinearly with smaller final TCSA. The percentage of cumulative fruit DW plus final tree DW in fruit increased curvilinearly with smaller final TCSA. Although 9 distinct rootstock genotypes of widely different vigors were included, the close relationships of tree DW and the distribution of DW between fruit vs. wood to final TCSA suggested that rootstock effects on both vigor and productivity were mediated through a single overall mechanism.