2017 ASHS Annual Conference

Supplemental lighting effectively promotes plant growth and yield of greenhouse tomatoes, particularly during winter months. Despite the significant importance, limited information is available as to how supplemental light source and quality interact with growth and yield of greenhouse tomato. The objectives of this study were to evaluate the impact of light source and quality on morphological and physiological characteristics of greenhouse high-wire tomato and to determine subsequent effects of such characteristics on plant water use. Intracanopy lighting from light-emitting diode (LED) towers was compared with that from overhead high-pressure sodium (HPS) lamps. Supplemental lighting treatments were composed of different combinations of red (R), blue (B), and far red (FR): B + R (39B: 61R:0FR), R alone (0B:100R:0FR), R + low FR (0B:82%R:18FR), R + high FR(0B:71R:29FR), HPS (38B:35R:27FR) controls, and un-supplemented controls. A fertigation leaching fraction of 30% was applied to maintain acceptable electrical conductivity (EC) and pH in the root zone. Daily water use (DWU) was calculated by subtracting the amount of leachate collected from individual plants from the amount of nutrient solution applied at each irrigation. Plant growth metrics (whole plant fresh weight, number of leaves, flowers, and fruits) and physiological metrics (leaf temperature, and stomatal conductance) were measured on a regular basis. At harvest, plant tissues were separated and dry weight was determined. HPS strongly promoted vegetative growth, and the fresh weight of whole plants was significantly higher compared to LED treatments. HPS-grown tomato plants had 25% higher water content in the leaves, and maintained leaf temperature similar to that of LED treatments, while exhibiting a significantly higher stomatal conductance only at the top of the canopy. Meanwhile, LED light containing FR hastened the reproductive growth phase of tomato plants, resulting in earlier flowering by one week and fruiting by two weeks compared to the HPS treatment. The morphological and physiological changes interacted with DWU of tomato plants. HPS tends to promote DWU during vegetative growth, but this trend was revered when tomato grown with LED supplemental lighting produced fruits earlier than HPS-grown plants. Supplemental LED containing FR maintained higher yield throughout production, resulting in a 1.5-fold higher yield than HPS treatment. It is concluded that supplemental LED lighting with FR leads to positive morphological and physiological changes, and therefore increases in yield of greenhouse tomato during winter months.