Growth and flower-bud formation in apple as affected by paclobutrazol, daminozide, and tree orientation in combination with various gibberellins

SummaryThe effect of paclobutrazol (1000 ppm), daminozide (1800 ppm), and the gibberellins GA3, GA4, GA7 and GA4+7 (500 ppm), applied alone or in various combinations on shoot growth and flower-bud formation was determined for one-year-old (two experiments) or two-year-old (one experiment) cv Cox’s Orange Pippin trees in pots. One experiment included tree position (vertical v. horizontal). Daminozide, paclobutrazol (when applied twice) and the horizontal position reduced shoot growth, but the GAs had little or no effect. In the year after treatments, growth of the paclobutrazol-treated trees was stimulated considerably. In the other treatment groups there was no pronounced after-effect on growth. GA3 and GA4 had little or no influence on flowering, whereas GA7 and GA4+7 greatly reduced it. Paclobutrazol stimulated flowering where the general level of flowering in the experiment was low or reduced by some other treatment (e.g. with GA7). Flowering was promoted in horizontally-positioned trees and to some degree after spraying with daminozide. A positive correlation was found between the weight ratio of vegetative to floral parts in individual flower buds on spurs and total shoot growth as affected by the various treatments. The reduction of flowering by GA7 was greatest on the basal parts of the shoots, at least in the horizontal and the daminozide-treated trees. The promotion of flowering by paclobutrazol and the horizontal position mainly concerned the upper half of the shoots.