OPTIMIZING GREENHOUSE TOMATO PRODUCTION: LIGHT AND THE PHYSIOLOGICAL DISORDER EDEMA

76 pagesGreenhouse production of tomatoes through the use of sophisticated environmental controls and precision hydroponic growing techniques allows for significantly higher yields within a smaller footprint when compared to traditional field production. One of the challenges faced by year-round greenhouse tomato operators in the Northeast U.S. is the low availability of solar radiation during the winter months, which results is a heavy reliance on supplemental lighting to maintain the photosynthetic processes required for suitable yields. During preliminary experiments evaluating multiple daily light integral (DLI) and CO2 combinations with juvenile tomato plants grown in acrylic miniature growth chambers under cool white fluorescent lights, we began to notice the development of the physiological disorder edema on the lower, oldest leaves. Multiple studies have evaluated the effect of light quality on the development of edema in tomato, with many finding a correlation between increasing rates of edema in UV-deficient environments. Given the UV-filtering characteristics of acrylic and a lack of literature evaluating the interaction of multiple cultivars to edema, the objective of our study was to evaluate the development of edema in one rootstock cultivar, ‘Maxifort’, and four hybrid scion cultivars: ‘Sweetelle,’ ‘Trust,’ ‘Merlice,’ and ‘Torero.’ We began our experiment with 4-week-old tomato plants, with two of each cultivar being placed into four identical acrylic miniature chambers and a remaining eight of each being grown in a control walk-in chamber with no acrylic. Each experimental replication lasted ten days, with plants being assessed for their edema index rating along with affected leaf count of the three oldest compound leaves every two days. At the conclusion of the experiment, plants were evaluated for fresh and dry weight, stem diameter, overall height and total leaf area. We found a significant variation in the edema index between cultivars, with ‘Maxifort’ and ‘Sweetelle’ expressing the most and least symptoms over the 10-day cycle, respectively. All three compound leaves evaluated had a higher edema index when exposed to the acrylic chamber treatment, with severity increasing with leaf age. All cultivars exposed to the treatment, to a different degree, experienced a reduction in fresh weight, dry weight, plant height, and total leaf area. The results of this experiment could have benefits in for selecting existing cultivars or new cultivars from plant breeding efforts with lower susceptibility to edema for greenhouse growers producing in climates that may be conducive to the disorder. In a separate study conducted to quantity the benefits of an increasing daily light integral (DLI) on commercial-style, high wire hydroponic tomato production, four greenhouses were established with four different lighting treatments (15, 20, 25 and 30 mol·m-2·d-1) and controlled using the Light and Shade System Implementation (LASSI) algorithm. Plants were exposed to the treatments for three months, with photosynthetic parameters (net photosynthesis, transpiration, stomatal conductance, and water use efficiency (WUE)) being evaluated three times during the course of the experiment. In addition, each plant was analyzed for number of clusters, number of fruit, total peduncle and fruit weight, first fruit fresh weight, first fruit Brix, first fruit dry weight, and the first fruit FW:DW ratio, with harvests being conducted as needed. From this study, we found no significant difference between treatments in the four photosynthetic parameters, although we did see a significant decrease in net photosynthesis over the course of the experiment. Likewise, there was a significant decrease in the number of harvested clusters, total cluster weight, fresh weight , dry weight, and the FW:DW ratio across the three months of harvest, with plants exposed to 25 mol·m-2·d-1 performed significantly worse that the 20 and 30 mol·m-2·d-1 treatments. This trend was inverted for Brix content, with the 25 and 15 mol·m-2·d-1 treatments having an overall higher average sucrose content than the others. Due to the interaction of increased plant age at start of the experiment, pressure from the root disease, Pythium, and increased environmental stress from high irradiance and heat in the summer, we believe that the experiment should be replicated with younger plants under winter conditions to ensure the best results are achieved. Identifying optimal DLI targets for tomato production can be beneficial for growers looking to determine the optimal light level to target without wasting additional energy on excess light that does not further contribute to yield