Abstract
Effects of light break treatment every second or third night on the growth of certain leaf vegetables were evaluated. In experiment 1, spinach (Spinacia oleracea) was irradiated with 0.4~1.2 μmol·m−2·s−1 (PPF) of light from an incandescent lamp for 51 minutes a mid-night every night (every night treatment), or for two hours at mid-night on Monday, Wednesday and Friday (interval treatment). In experiments 2, spinach and tsukena (Brassica campestris) received interval treatment with 1.0-1.5 μmol·m−2·s−1 of light of incandescent lamp for two hours at mid-night. In experiment 3, spinach, lettuce (Lactuca sativa) and tsukena received interval treatment with 0.5-1.8 μmol· m−2·s−1 of light from light emitting diodes (LEDs) for two hours at mid-night.
In experiment 1, under interval treatment, there was no bolting of spinach on the 26th day of treatment. However, ratio of bolting plants was 22 % under every night treatment. In experiments 2 and 3, interval treatment with incandescent lamp or LED promoted spinach growth without bolting. In spinach, plant height, number of leaves and top dry weight were larger under interval light break treatment than under no light break. However, the growth of lettuce and tsukena were not promoted with light break treatment.
