2017 ASHS Annual Conference

Rates of primary and secondary metabolism, the latter affecting well-known compounds contributing to nutritional value and sensory appeal, are rarely high simultaneously. However, promoting both within the same cropping cycle can benefit growers and consumers in multiple ways. The process is difficult, perhaps especially in fall-to-spring high tunnel production in mid to upper latitudes known for dynamic and often limiting temperature and light conditions. This research examines the extent to which aboveground biomass and anthocyanin concentrations are affected by microenvironments imposed during specific portions of baby lettuce and choi production cycles. The experiment was repeated Oct-Dec and Feb-Apr in 2015-2016 and 2016-2017 in a single-layer, 9.1 m x 24.4 m high tunnel located at the Ohio Agricultural Research and Development Center in Wooster, OH. Twenty, 4.46-m² main plots were divided into 2.23-m² subplots, each containing either ‘Outredgeous’ lettuce (Lactuca sativa) or ‘Red Pac’ choi (Brassica rapa var. chinensis) direct-seeded at 3,875 seeds/m² on 10/9/15, 2/16/16, 10/7/16, and 2/21/17. Each subplot was assigned to one of five treatments based on when they were covered with standard, vented (178 1-cm holes/m²), 1.1 mil polyethylene film: 1) uncovered all 8 weeks, 2) covered first 4 weeks, 3) covered middle 4 weeks, 4) covered last 4 weeks, and 5) covered all 8 weeks. Analyzing digital images obtained biweekly assisted in calculating percent canopy cover and plant density. Air and soil temperatures were recorded every 15 minutes using Hobo U23 Pro v2 External Temperature Data Loggers. Destructive sampling of a 0.093-m² quadrat within each subplot at 2, 4, 6, and 8 weeks after seeding permitted the measurement of fresh and dry weight, anthocyanin concentrations, soluble solids, leaf area (cm²), and average daily growth rate. Lettuce and choi data from spring and fall of 2016, especially of Treatments 1, 3, 4 and 5, provide additional evidence that yield and anthocyanin levels are usually negatively related, although this result varied slightly with season. Interestingly, Treatment 2 resulted in moderately high yield and anthocyanin levels in both seasons. Overall, these data indicate that the timing of certain microenvironments within the cropping cycle are likely to affect processes underlying the relative accumulation of aboveground biomass and anthocyanin. More specifically, the data suggest that promoting growth early in the cycle and secondary product accumulation late in the cycle may result in the much-needed balance between yield and quality.