Scientific publications

A daily short-term temperature drop in the end of the night or in the morning is commonly used in greenhouse production of transplants of a number of vegetable and bedding plants and ornamental plants for plant height control as an alternative to chemical growth retardants. The aim of this work was to quantify the effects of a temperature drop at different times of the day and night on growth, photosynthetic activity and chilling tolerance of cucumber (Cucumis sativus L.) and tomato (Solanum lycopersicum L.) plants. Plants were grown under air temperature of 23 °C, a photoperiod of 12 h under controlled environmental conditions in growth chambers with a photosynthetic photon flux density of 200 µmol m-2 s-1. Starting from the 7th (for cucumber) or 14th (for tomato) day from seed soaking, plants were on each of the following 6 days exposed to a temperature of 10 °C for 2 h at the beginning, in the middle and in the end of the night and at the beginning, in the middle and in the end of the day. The results show that temperature drop treatments retard the linear growth of the plants regardless of their timing in the daily cycle. The optimal time for temperature drop treatments in order to obtain compact plants may not coincide with the periods of the highest growth rate of the stem as a temperature drop itself is capable of modifying the course of plant growth in the daily cycle. Light conditions during the chilling treatment (light or darkness) rather than diurnal variation of plant sensitivity to chilling are responsible for plant response to temperature drop treatments. The resultant data confirm the presence of a well-pronounced species specificity in plant responses to a daily short-term temperature drop.