Rootstock, Canopy Architecture, Bark Girdling, and Scoring Influence on Growth, Productivity, and Fruit Quality at Harvest in 'Aztec Fuji' Apple

The increasing scarcity of land and water for agriculture mandates an efficient use of these natural resources. Establishment of high-density orchards with the use of a size-controlling rootstock, in combination with a suitable canopy architecture, is an efficient method for fruit production. However, less attention has been paid to the use of size-controlling practices such as trunk girdling in these modern orchard systems. The impacts of two rootstocks, two tree architectures, and three levels of bark cambium cuts (girdling or scoring) on growth, yield, fruit quality attributes at harvest, and leaf nitrogen (N) in 'Aztec Fuji' apple (Malus domestica Borkh.) were studied in 2015 and 2016. Trees on Nic 29 had larger canopies, higher yields, and larger fruit, but lower fruit color, sunburn, and firmness than those on Bud 9. Trees with a tall spindle (TS) architecture had higher yield in 2016, higher fruit soluble solids and firmness in 2015, higher fruit russet in 2016, but shorter terminal growth in both 2015 and 2016 and lower leaf N in 2015 than did those with a central leader (CL) training system. Trees receiving a bark girdling in 2015 (BG15) or score girdling in 2015 and 2016 (SG1516) had significantly higher yield than trees on nongirdled trees (NOGD) in 2016. Bark girdling or score girdling in 2015 (BG15 or SG15) increased fruit weight (size), color, and firmness at harvest in the same year, although differences for score girdling were not always significant. However, BG15 or SG15 did not have a "carryover" effect and did not affect fruit size, color, or firmness at harvest in 2016. When bark scoring was repeated in 2016 (SG1516), fruit size was increased in 2016. On the basis of the results of this 2-year study, it appears that bark girdling in one year is sufficient to increase fruit size of the current year and the yield in the following year. If larger fruit size is the critical objective of fruit production, annual score girdling needs to be practiced. However, a further long-term study is needed to monitor the carryover effects of cambium girdling and scoring on tree performance and fruit quality attributes in the subsequent years.