FLOWER-BUD FORMATION IN APPLE AS AFFECTED BY AIR AND ROOT TEMPERATURE, AIR HUMIDITY, LIGHT INTENSITY, AND DAY LENGTH

Under controlled conditions, 3-year-old apple trees cv Cox’s Orange Pippin were exposed to various regimes of air and root temperature, relative air humidity, light intensity, and day length for periods of 3–4 months starting at full bloom.

Shoot growth was reduced and flowering was stimulated at an air temperature of 16°C as compared with 22°C, and at low versus high air humidity given in the first 8–9 weeks after bloom.
Markedly fewer flower buds were formed at reduced light intensity during the 7 weeks following bloom, but shoot growth was not affected.
Decreasing or increasing of the temperature, humidity, or light intensity later in the season had hardly any or no influence, which underscores the importance of the period immediately after bloom for flower-bud formation, i.e., the period prior to the actual process of flower morphogenesis.

In the range of 6–30°C, shoot growth increased linearly with root temperature, whereas for flowering the optimum root temperature proved to be about 15°C. A distinct reduction occurred at 30°C.

Growth and flower-bud formation were much better under long (14 h) than under short (8 h) day conditions.

An attempt was made to relate the present findings to current concepts of flower formation in apple.

Flowering and Fruit Set in Fruit Trees

J. Tromp

https://doi.org/10.17660/ActaHortic.1984.149.3