LED versus HPS Supplemental Lighting Effects on Fruit Quality of Greenhouse Tomato

Seasonal variation in solar daily light integral (DLI) makes it logistically and financially burdensome to produce greenhouse-grown tomatoes during the winter in a northern climate. A study is underway investigating interactions among light quantity and spectrum, fruit yield, flavor development, and composition of tomato fruit comparing supplemental lighting from energy-efficient LED intracanopy lighting vs. traditional overhead high-pressure sodium lighting vs. unsupplemented controls. Two tomato cultivars, ‘Success’ and ‘Kommeet’, were grafted onto the rootstock ‘Maxifort’ and grown in soilless slab culture within a greenhouse using high-wire trellising. A tomato-production experiment was conducted from late January to late June, 2012 with increasing solar DLI combined with a constant supplemental DLI of 9 moles per meter squared per day. Fruits were harvested at the vine-ripe stage, counted, and weighed. Quality metrics were selected that are standard in the Horticultural and Food Science Industries.  Objective measures of fruit quality included total soluble solids, titratable acidity, pH, electroconductivity, chromatic index, lycopene, and anti-oxidant contents.  These attributes were linked to consumer acceptance via subjective organoleptic taste panels.  Both hedonic (indicating preference) as well as absolute scales of evaluation (without indicating preference) were used to evaluate tomato fruit for flavor characteristics including sweetness, acidity, texture, aroma, bitterness, aftertaste, color, and overall approval.  Both subjective and objective metrics of fruit quality were correlated with type of supplemental lighting used, total DLI, cultivar, and time of year when harvested.  Results from the first fruit-production experiment conducted in 2012 will be presented. This project is supported in part by NIFA SCRI grant 2010-51181-21369.