THE PATTERN OF HORMONES OF INTACT APPLE SHOOTS AND ITS CHANGES AFTER SPRAYING WITH GROWTH REGULATORS

Intact spurs and annual shoots of apple trees /McIntosh and Jonathan cvs/ and those sprayed with growth regulators /McIntosh and Melba cvs/ were analyzed for endogenous levels of auxin, gibberellin and cytokinin-like substances on six or four dates, beginning from the fourth week after full bloom.
Hormones extracted with ethanol from soft, growing parts of spurs and annual shoots were purified, and partitioned by TLC then determined by specific bioassays.

No significant differences were found in auxin levels between fruiting and non-fruiting spurs.
A high level of gibberellins occurred in the former while cytokinins prevailed in the latter.
Treatments of the trees with gibberellic acid brought about a decrease in cytokinin level of the spurs.
A mixture of succinic acid-2, 2-dimethylhydrazide /SADH/ and Ethrel /1000 and 500 mg/l/ caused an abrupt decrease in endogenous gibberellins and an increase in cytokinins, whose level reached a maximum about a month later.
In annual shoots an increase in cytokinins after treatments with growth retardants was preceeded by their fall.
A direct relationship was found between the ratio of endogenous cytokinins to gibberellins and the ability of the shoots to produce flower buds.
The role of the ratio of these two hormones in flowering is discussed.

Flowering and Fruit Set in Fruit Trees

M.J. Grochowska, A. Karaszewska, B. Jankowska, A. Mika

https://doi.org/10.17660/ActaHortic.1984.149.2