GROWTH RHYTHM AND TEMPERATURE DROP

The effects of a short temperature change or a dark interruption on plant morphogenesis and flowering were studied in two experiments on Begonia x hiemalis. A 2-h temperature increase at the beginning of the day or towards the end of the night increased plant height compared to a constant temperature.
Corresponding 2-h temperature drops reduced the plant height.
A temperature drop at the beginning of the night resulted in a similar internode length as a temperature decrease towards the end of the night, while treatments in the middle of the night were less effective.
There was an approximate interval of 12-hours between temperature drop treatments in the night period when the plants showed the greatest reduction in stem elongation.

Start of a 90-min dark interruption five hours before sunset resulted in the shortest internode length and the fewest number of flowers per plant.
Dark interruptions earlier or later in the day increased both internode length and number of flowers.
The results indicate that there is at least one rhythm in sensitivity to environmental factors regulating the stem elongation in Begonia x hiemalis (see Grindal and Moe, 1993 for details).

A third experiment is described, which measured the stem elongation in Euphorbia pulcherrima with an angular displacement transducer.
Preliminary results indicate a circadian rhythm in the stem elongation rate of this species.
The relationship between temperature drop and growth rhythm is discussed.

Workshop on Environmental Regulation of Plant Morphogenesis

G. Grindal, R. Moe

https://doi.org/10.17660/ActaHortic.1995.378.6