Effects of air temperature regimes on physiological disorders and floral development of tomato seedlings grown under continuous light

Abstract

Providing continuous light (24-h photoperiod) at a relatively low photosynthetic photon flux (PPF) is one possible way to reduce both initial and operational costs for lighting and cooling during transplant production with an artificial light. However, physiological disorders (i.e., chlorosis and necrosis) are often observed in several species under continuous light with a constant temperature. The objective of this study was to find an effective air-temperature regime under the continuous light to avoid such physiological disorders, and simultaneously enhance floral development, using tomato [Lycopersicon esculentum Mill.] as a model. The seedlings with fully expanded cotyledons were grown for 15 d at a PPF of 150 μmol·m -2·s-1, a relative humidity of 70%, and a CO 2 concentration of about 380 μmol·mol-1 (atmospheric standard). Leaf chlorosis was observed when the air temperature was constant regardless of average air temperature (16, 22, or 28°C). Neither leaf chlorosis nor necrosis was observed when the air temperatures were alternated [periods of high (28°C) and low (16°C) air temperatures of 16/8, 12/12, and 8/16 h·d-1). Faster floral development was observed in the seedlings grown at lower average air temperatures. These results indicated that physiological disorders of tomato seedlings grown under continuous light could be avoided, and at the same time floral development could be enhanced, by lowering the average air temperature through modification of the periods of high and low air temperatures.