Effect of dark period lighting regulation on cucumber seedling morphology and comprehensive evaluation analysis and comprehensive evaluation

Abstract: To ascertain light quality and light duration at dark duration and its influence on the growth and morphological of cucumber seedling, light-emitting diodes lights were taken as supplemental light at dark period for cucumber (Cucumis sativus L. cv. Cumlaude) seedlings to study in this paper. According to the influence confirmed by using comprehensive evaluate method, suitable light quality and light duration were selected. Cucumber "Jin Chun Ⅳ" seedlings were planted in greenhouse with or without supplemental light during dark period for two groups of experiments. In the first group of experiments, the treatments were 4 types LED light, L1 (70%R, 30%B), L2 (80%R, 20%B), L3 (90%R, 10%B), L4 (100%R) , which supplementing light times were 2 h (19:00-21:00), 4 h (19:00-23:00) and 6 h (19:00-01:00) respectively during dark period, and no supplemental light in dark period were taken as control (CK). And in the second group of experiment, the treatments were two types LED light, L2 and L4, which supplementing light times during dark period for 4h, and no light in dark period was taken as control (CK). Both in the two groups of experiment, these indexes including hypocotyls length, cotyledon area, stem diameter, leaf area, seedling height, dry weight, chlorophyll content, seedling index and root shoot ratio of cucumber seedlings were investigated and were used to comprehensive evaluate and analyze the effect of light quality and light duration on the growth of cucumber seedlings. The results showed that, light quality affected hypocotyls length and stem diameter significantly at 0.05 level, and affects seedling height, leaf area, chlorophyll, dry weight and seedling index significantly at 0.01 level. Light duration had significant effect on seedling index at 0.05 level and significant effect on hypocotyls length, seedling height and dry weight at 0.01 level. Light quality and light duration had significantly interaction effects on hypocotyls length, seedling height and stem diameter at 0.01 levels and significantly interaction effects on seedling index at 0.05 levels. Hypocotyls length of seedlings under L2 for 4h in all treatments was shortest and was 25.14% less than CK, chlorophyll content, dry weight and seedling index of seedlings under L2 for 4 h were largest in all treatments and was 17.34%, 58.33% and 175.28% more than CK respectively. Seedling height under L3 for 2 h was shortest in all treatments and was 22.97% less than CK. Leaf area of cucumber seedlings under L4 for 4 h was largest in all treatments and was 19.10% more than CK, cucumber seedlings stem diameter under L1 for 6h was thickest in all treatments and was 44.52% more than CK, and root shoot ratio of seedlings under L3 for 4h was largest in all treatments and was 41.18% more than CK. According to comprehensive evaluation analysis, comprehensive evaluation value of cucumber seedlings under L2 light quality for 4 h was largest and quality of cucumber seedling was best. In addition, L4 light quality promoted seedling leaf area and stem diameter of cucumber seedlings to increase at early stage (one-leaf stage and two-leaf stage) of seedling, and L2 light quality promoted leaf area and stem diameter to increase at later stage (adult stage) of cucumber seedlings. In conclusion, the most suitable supplemental lighting time during dark period for cucumber seedlings was four hours. The most suitable light quality for cucumber seedling at early stage (one-leaf stage and two-leaf stage) was L4, and the most suitable light quality for cucumber seedling at later stage (adult stage) was L2. This provides the basis for the regulation of cucumber seedling morphology and the designing of supplemental lighting devices.