Effects of temperature-drop and a short dark interruption on stem elongation and flowering in Begonia × hiemalis Fotsch

Abstract

The effects of a short temperature change or dark interruption on plant morphogenesis and flowering in Begonia × hiemalis Fotsch were studied. A 2 h temperature increase in the morning increased the plant height. A corresponding temperature decrease (temperature-drop) at the beginning or toward the end of the night period, or at daybreak reduced the plant height and the internode length, but in the middle of the night the effect of temperature-drop was small. There was approximately a 12 h interval between the times in the night period with the greatest effects of temperature-drop on internode elongation. Temperature-drops to 16.1°C and 13.2°C decreased the internode length compared with a constant temperature (19.2°C). The effect was greater at 13.2°C than at 16.1°C. A 90 min dark interruption 5 hours before sunset resulted in the shortest internode length and fewest flowers and flower buds per plant. A dark interruption earlier or later in the day increased internode length and flower number. The role of endogenous rhythms on stem elongation and flowering in Begonia × hiemalis is discussed.