ISHS Acta Horticulturae 239: VI International Symposium on Growth Regulators in Fruit Production
REGULATION OF FRUIT SET IN TREE FRUITS WITH PLANT GROWTH REGULATORS |
| Author: | Duane W. Greene |
| Abstract:
Paclobutrazol is unique among presently used growth regulators since it can either thin the year of application as a foliar spray or it can, as a carry-over effect, increase fruit set the years following application. The thinning response appears to be concentration independent above a threshold value, and the suggested mode of action is by acceleration of embryo abortion. Shading or compounds which inhibit photosynthesis also cause thinning, indicating that a stress caused by starving fruit may increase thinning. Greater thinning occurred on trees that were both chemically thinned and shaded. The practical significance is that several days of cloudy weather following thinner application may be as effective as temperature stress at enhancing effects of chemical thinners. Cytokinins, particularly benzyladenine, show promise as chemical thinners on apples since they not only thin, but also increase fruit size and enhance return bloom. Hormone sprays containing a gibberellin, an auxin, and a cytokinin increase fruit set. Ovule longevity and viability appear to be key factors determining the success of these hormone sprays. Polyamines increase fruit set of apples if applied near full bloom. They may be acting through some influence on ethylene biosynthesis or by delaying ovule senescence. Application techniques that target certain portions of a tree may be useful for more precise and effective thinning. Temperature may modify responses to growth regulating chemicals. | |
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