CHEMICAL CONTROL OF FRUIT SET AND JUNE DROP OF PEAR TREES WITH PP 528 AND PP 938

Two years of researches were carried out using two new experimental growth regulators (PP 528 and PP 938) combined or not with different pruning techniques, in young "Passe Crassane" and adult "Conference" pear trees on quince A.

PP 528 (50–300 ppm) applied in May, when the shoots of the "Passe Crassane" trees were 15 cm long, greatly showed-down the growth of the shoots and promoted the feathers formation; it also reduced the fruit bud differentiation for the subsequent year, probably in relation with an increase of GA-like substances and inhibiting substances found in the shoot tips, few days after the treatment.

As interaction between PP 528 and winter pruning, fruit-set in the subsequent year was significantly increased as compared with the effect of pruning alone, the June-drop instead decreased.

PP 938 (1,500–5,000 ppm) applied in May on "Conference" trees, had quite a good influence only to prevent June-drop for both years (at least the lowest concentrations). Although the shoot growth was significantly reduced in the first year, in the second year the new shoots increase supplied the delayed growth of the previous year.
Various effects has been noted on the fruit bud differentiation.
The bioassays showed a significant increase of the gibberellin-like substances (specially two weeks after the treatment, during the second year) in the shoot tips as well as in fruits, and temporary decrease of the auxin-like substances.

II International Symposium on Pear Growing

S. Sansavini, G. Cristoferi, N. Filiti

https://doi.org/10.17660/ActaHortic.1977.69.29