EFFECT OF DIURNAL TEMPERATURE ALTERNATIONS ON PLANT MORPHOLOGY IN SOME GREENHOUSE CROPS - A MINI REVIEW

In recent decades, chemical growth retardants have been used to control plant morphology in many greenhouse crops. Research is currently underway to find other practical means of regulating plant morphology. Efforts have concentrated on temperature control, which could result in well-shaped plants without a delay in flowering. The difference (DIF) between day temperature (DT) and night temperature (NT) influences internode length, plant height, leaf orientation, shoot orientation, chlorophyll content, lateral branching and petiole and flower stalk elongation in plants. Internode length increases as DIF increases. The response of stem elongation to DIF is greater when DIF increases from zero to positive, than from negative to zero DIF. DIF has the greatest effect on plant height during the period of rapid growth in determinant crops. Furthermore, the responses to DIF are rapid, and most plants respond to a change in DT and NT within 24 h. The effects of DIF on stem elongation and leaf expansion are a result of increased cellular elongation rather than division. In some long day plants (LDP), DIF has only a minor influence on flower initiation. The effect of negative DIF on flowering is different in the shortday plant poinsettia, where negative DIF delays flowering significantly. DIF interacts with light quality, light intensity, photoperiod and growth retardants, but not with water stress. A physiological explanation for the effects of DIF suggests that DIF may elicit responses through affecting the concentration of endogenous gibberellins (GAs). Stem elongation is also sensitive to a temperature drop in the last 2 h of the night or the first 2 h of the day. In Begonia X hiemalis Fortsch., temperature drop interacts with irradiance. Interaction between growth factors may be the reason that the effects of DIF and temperature drop on plant morphogenesis differ between research reports. Average daily temperature (ADT) can influence internode elongation in some species. Leaf unfolding rate is affected by ADT and not by DIF. The plant stem elongation rate is not constant during a day/night cycle and this knowledge can be used for control of plant morphogenesis and flowering by DT and NT alternations. This review shows that DIF and temperature drop can reduce or eliminate the use of growth retardants in many greenhouse crops.