The Influence of Apple Rootstock Genotypes on the Cultivar Tree Performance, Productivity, Fruit Quality, and Mineral Nutrition

The increasing world population and decreasing suitable land and water require significant increases in the fruit productivity and quality. One strategy is through the establishment of high-density orchards using size-controlling rootstocks.  Rootstocks can affect a range of pomological characteristics of the scion cultivar. The objective of this research was to study the long-term impact of several rootstocks on precocity, yield, and fruit quality attributes and leaf mineral nutrition of the scion cultivars through different projects over several years. Rootstocks included standard commercial cultivars (M-9, Bud-9, etc.), newly released Geneva cultivars and other test rootstock genotypes. ‘Aztec Fuji’ tees on 70-20-20, B.67-5-32, CG.4004, CG.3001, and PiAu5111 had the largest trunk cross sectional area (TCSA) but those on B.7-20-21 and B.71-7-22 had the smallest TCSA. Trees on G41N, 935N, and CG4004 often had high yields, but those on PiAu9-90 and B.71722, and B.7-20-21 had the least production.  Trees on CG.4003 and G11 were among the most yield efficient (yield in kg/TCSA) and crop efficient (fruit no/TCSA) trees. Trees on B.7-20-20, and PiAu990 were among the least yield-efficient trees. Trees on G.41N, and CG3001, CG.4004 often had the largest fruit while those on B.7-20-21, CG.4003, and PiAu990 had smallest fruits. Fruit from trees on B.7-20-21 had the highest soluble solids concentration (SSC) and firmness because of their smallest size. Trees on B.70-20-20 were among those with the least color, SSC, and firmness among trees on all rootstocks. Fruits on G11N and G11TC had more advanced starch degradation pattern (SDP) while those on CG2034 and CG.5087 had the lowest SDP than those on other rootstocks. Rootstocks affected apple leaf mineral concentrations. ‘Gala’ trees on more vigorous rootstocks such as G30 had higher leaf K.  Leaf sampling for mineral analysis in trees on dwarf trees could be taken earlier than those on vigorous ones. Rootstocks also influence the fruit mineral nutrition. Fruit with higher nitrogen and lower calcium was rootstock dependent and was associated with less color development and poor storage life. Rootstocks substantially affect important horticultural traits that impact overall tree productivity, quality and the ability to store that fruit.  As more rootstock cultivars become available commercially, it will be critical to identify the rootstocks that are the most compatible with major commercial apple varieties to better guide nursery propagation efforts and industry planting strategies.