Effect of Gibberellin Application to Current-year Saplings on Shoot Elongation and Flower Bud Formation in Following Year in Columnar Apple Morioka No. 74

The aim of this study was to reveal the effect of gibberellin application to the apical part of current-year saplings on shoot growth and flower bud formation in the following year in columnar apple Morioka No. 74. The application schemes were 5-times-application of 100 mg 2.7% gibberellin or 10-times-spray of 300–500 ppm gibberellin solution during the growing season. When saplings were not transplanted, the paste application reduced elongation of the main shoot but increased flower bud formation of the other lateral shoots in the following year. Continued paste application in the following year canceled the reduction of shoot elongation, but sapling heights were not different between both-year-application and second-year application. This result indicated that second-year application is efficient for shoot growth promotion in two-year raising. If saplings were transplanted, similar following-year-reduction of main shoot elongation was observed irrespective of application schemes. However, sapling heights and numbers of lateral shoots and flower buds of applied saplings were larger than in non-applied controls after following-year-growth. Since the application of pastes or 500-ppm solution significantly reduced root biomass accumulation in the current year, non-applied controls with larger root systems may be severely damaged even by regular transplanting, which can also decrease shoot elongation in the following year. Considering these results, even in one-year raising, it is suggested that growth promotion by the application schemes contributes to early increases in tree crowns and fruiting parts in columnar apple.