Leaf Injury and Dry Mass Production in Eggplant and Pepper Plant as Affected by Overnight Supplemental Lighting

Abstract

Effect of overnight supplemental lighting at different light intensities following natural day length on growth and leaf injury of eggplant and pepper plant was investigated. Leaf chlorosis was observed with over 35 μmol m-2 s-1 PPFD and there was no correlation between light intensity and dry matter production in eggplant. On the other hand, pepper plants grew vigorously without any injurious symptoms even at 200 μmol m-2 s-1 PPFD. Total dry weight in pepper plant increased linearly with increase in light intensity. For instance, when supplemental light intensity was 100 μmol m-2 s-1, dry weight increase was 1.57 g/plant at 3 weeks after the initiation of light treatment, which was about 2 times higher than that in natural dark control (=0.71 g/plant) . When light intensity was 200 μmol m-2 s-1, the increase rate of total dry weight was 3 times higher than that in natural dark control. Increase rate of root dry weight was 4 times, but root length in the longest root was not different between the two treatments, suggesting that the lateral root growth was promoted by supplemental lighting. When sunlight intensity was reduced by 50%, the dry weight increase rate was 1.6, 1.5 and 2.0 times for leaf, stem and root, respectively, against 1.3, 1.2, 1.3 times in non-shaded plants. These results indicate that the enhancement of dry mass production in pepper plants by overnight supplemental lighting is more profound when the daytime solar radiation is low.