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  • Author or Editor: Peter Ling x
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Bedding plant petunia (Petunia ×hybrida) is often produced with high nutrient concentrations as a cool-season crop. How a plant uses the nutrients supplied will depend in large part on the environmental factors influencing growth rate, such as light and CO2. Since more growers are considering using supplemental CO2 to improve energy efficiency for plant production, it is important to understand light and fertilizer levels needed for efficient production of high-quality plants. Using a multi-chamber controlled environment system, petunia plants were grown from seed for 6–8 weeks after transplanting into different light and CO2 environments and fed with either a low (7.1 mM N) or high (21.3 mM N) fertilizer regime. Plants were evaluated for appearance, harvested periodically, and separated into flower, stem, and leaf biomass. Biomass was then dried and analyzed with ICP-OES for essential macro- and micronutrients. Low-fertilizer-grown plants had consistently earlier and more flowers, but showed symptoms of nutrient deficiencies in the final few weeks of production at all light and CO2 levels. There were significant interactions between light and fertilizer treatments for different nutrients. Calcium uptake was greatly influenced by light level, Fe, P, and K were influenced by the fertilizer supply, and Mg and B were inversely influenced by fertilizer supply at high light. These data suggest new management strategies are needed to improve fertilizer use efficiency in different environments.

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Fuel prices have fluctuated wildly in the last several years, and faced with unpredictable or rising fuel costs, growers often lower temperature set points to decrease fuel use. However, plant growth and development are influenced by lower temperatures and may actually cause increases in fuel use as a result of longer production times. Alternative strategies to efficient crop production are needed. Fertility, light, and CO2 are other environmental factors that can be manipulated within a greenhouse but how all three interact together on growth and development are surprisingly not well known. Petunia ×hybrida Vilm. were grown in controlled environments in a 2 × 2 × 2 factorial study investigating how light, fertility, and CO2 influence growth and development, including shoot partitioning, nutrient uptake, and carbohydrate concentration. Generally, light enhanced flowering, both mass and fraction of total biomass, whereas increased fertility was detrimental to the proportion of biomass allocated to flowers. The influence of CO2 was complex with high CO2 suppressing flowering and enhancing leaf growth, but only midway through the 7-week experiment. Carbohydrate concentration remained high in elevated CO2, even when light and fertility were not limiting. This suggests a sink limitation, so even in high light and fertility, crop response to enhanced CO2 was low. Although CO2 had no size effect late in growth, CO2 suppressed nutrient concentrations. Together, these data suggest strategies that growers may have in controlling their crop growth and development and indicate that enhanced growth (leaf and steam mass) may be at the detriment of development (flowering mass and allocation).

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Leaf samples collected from field plots of nine lettuce varieties established in the Early (ES) and Late (LS) Summer of 2002 and 2003 in Celeryville, Ohio, were subjected to spectrophotometric measurement of anthocyanin concentrations and/or color analysis based on colorimeter and spectroradiometer readings and human panelist ratings. Interactions between year (Y), planting date (PD), and variety (V) main effects for anthocyanin concentration were significant due to shifts in response magnitude, but not direction. Anthocyanin levels were higher following LS than ES planting, regardless of Y and V, and PD effects were pronounced in 2002, when differences in average daily temperature between ES and LS plantings tended to be larger. Also, regardless of Y and PD, anthocyanin levels followed the pattern `Impuls' > `OOC 1441' > `Valeria' > `OOC1426' > `Lotto' > `SVR 9634' `OOC 1434' > `OOC 1310' > `Cireo'. Treatment-based color differences were also evident in colorimeter and spectroradiometer readings. And, panelists differentiated field-grown samples based on red color intensity. Strong correlations between analytical and instrumented and human panelist-based measures suggest that instrumented assessments of red color intensity may serve as reliable proxies for direct measures of anthocyanin levels or human panelist ratings, particularly if the aim is to establish color differences between major experimental groups and assign a quantitative, repeatable value to red color intensity.

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Yield reduction resulting from high temperatures and tipburn are common issues during the summer for hydroponically grown lettuce using the nutrient–film technique (NFT). We investigated the yield and degree of tipburn of lettuce ‘Red Butter’, ‘Green Butter’, and ‘Red Oakleaf’ of the Salanova® series under different-solution electrical conductivity (EC) and pH levels. We also quantified the effect of foliar spray application of calcium chloride (CaCl2) on the yield and degree of tipburn using the lettuce cultivar Green Butter. For the EC experiment, the plants were grown at four EC levels (1.4, 1.6, 1.8, or 2.0 mS·cm–1) and a constant pH of 5.8. For the pH experiment, the plants were grown at and four pH levels (5.8, 6.0, 6.2, or 6.4) and a constant EC of 1.8 mS·cm–1. For the foliar spray experiment, CaCl2 was applied 1 week after transplanting into NFT channels at three different concentrations: 0, 200, 400, or 800 mg·L calcium (Ca). During the EC trial, the maximum yields were observed at or more than 1.8 mS·cm–1 for ‘Green Butter’ (263 ± 14 g/head) and ‘Red Butter’ (202 ± 8 g), and more than 1.6 mS·cm–1 for ‘Red Oakleaf’ (183 ± 6 g). The yield of ‘Green Butter’ was 75 g less at 1.4 mS·cm–1 compared with 1.8 mS·cm–1. Tipburn symptoms were less at 1.4 mS·cm–1 for ‘Green Butter’ whereas other cultivars were not highly susceptible. In pH trials, the maximum yield for all cultivars was found at pH 6.0 and 6.2. There were no differences in tipburn symptoms among all pH levels. The foliar spray treatment, twice a week at 400 or 800 mg·L–1 Ca, provided improved tipburn control, as the tipburn symptoms were minimal and the impact on yield was minor compared with reducing EC. This series of experiments found evidence in proper EC and pH management for optimum yield and tipburn control in NFT lettuce grown in summer conditions.

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Water jet technology to slice carrots or salt treatment prior to slicing was studied to minimize the unappealing whitish tissue noted with carrot sticks. The water jet was a fine stream with 378,950 kPa force. Salt treatment consisted of immersing carrots in NaCl solution ranging from 0.0 to 1.0 M concentration for 3 to 20 hours. Subsequently, the carrots were sliced, stored at 5 C, and analyzed. Carrot sticks sliced with the water jet had a greater amount of white tissue than those sliced with a knife. Scanning electron microscopy showed that the water jet caused grooves on the cut surface, which exposed many layers of cells to dehydrate rapidly. The grooves probably can be minimized by increasing the speed of slicing. Salt treatments of 0.5 to 1.0 M concentration caused 3 to 10 percent weight loss when treated for 20 hours at 5 C or 3 hours at 20 C. Carrot sticks with increased weight loss had less whitish tissue and had an appearance of freshly cut sticks; however, the textural quality decreased.

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In addition to their physiological and metabolic roles, anthocyanin (Antho) levels in lettuce contribute to visual and nutritional value-based assessments of crop quality. Although 7 genes are now thought to help regulate Antho synthesis, deposition and/or degradation in lettuce, the genetic and abiotic controls of Antho levels remain less well characterized in lettuce than other plants. Previous greenhouse studies demonstrated that Antho levels in diverse lettuce varieties are a function of temperature and lighting regimen. Here, three strongly related Lolla Rossa-type varieties (`Lotto', `Valeria', and `Impuls') varying in the number of genes controlling intensity of anthocyanins were subjected to differential temperature conditions in growth chambers to better discern the independent and interactive effects of temperature (T) and variety (V) on Antho levels. Fifteen day-old seedlings were placed into one of three chambers maintained at 20 °C day/night (D/N), 30 °C/20 °C D/N or 30 °C D/N. Antho levels were measured in leaf tissue collected 30 d after transplanting. The entire experiment was replicated twice. Although significant, the T x V interaction resulted from differences in the magnitude, not direction, of the change in Antho concentrations among varieties with changes in T. This suggests that T was a main driver of Antho levels in this study. Regardless of V, Antho concentrations were highest, moderate and lowest after growth at 20 °C D/N, 30 °C/20 °C D/N and 30 °C D/N, respectively. Likewise, regardless of T, Antho levels followed the pattern `Impuls' (three genes) > `Valeria' (two genes) > `Lotto' (one gene). Correlations among instrumented and human eye-based evaluations of color are also being tested in samples from both studies.

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Anthocyanins (Antho) are the source of red color in plants and the intensity of redness is an important quality parameter in red leaf lettuce. Despite the importance of Antho in leaf lettuce, little information is available regarding the effects of major production-related factors, such as planting date, on their levels. To address this issue, field studies were conducted in 2002 and 2003 in which Antho levels were measured in nine lettuce varieties planted in early and late summer (ES and LS, respectively) using a RCB design. Leaf tissue was sampled 30 d after transplanting. Data for three strongly related Lolla Rossa-type varieties (`Lotto', `Valeria', `Impuls') are reported here. The planting date × variety interaction was significant; however, Antho concentrations were higher following planting in LS than ES, regardless of variety. Planting date effects were more pronounced in 2002, when differences in average daily temperature between ES and LS plantings tended to be larger. Regardless of planting date and year, Antho levels followed the pattern `Impuls' (three genes) > `Valeria' (two genes) > `Lotto' (one gene). Correlations between human visual and two types of instrumented assessments of color are being tested in samples from the same study.

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Leaf samples collected from field plots of nine lettuce cultivars established in the early (ES) and late (LS) summer of 2002 and 2003 in Celeryville, Ohio, were subjected to spectrophotometric measurement of anthocyanin concentrations or color analysis based on colorimeter and spectroradiometer readings and human panelist ratings. Interactions among year (Y), transplanting date (TD), and cultivar (C) main effects for anthocyanin concentration were significant as a result of shifts in response magnitude but not direction. Anthocyanin levels were higher after LS than ES transplanting regardless of Y and C. The effects of TD were pronounced in 2002, when differences in average daily temperature between ES and LS transplantings tended to be larger. Also, regardless of Y and TD, anthocyanin levels followed the pattern ‘Impuls’ > ‘OOC 1441’ > ‘Valeria’ > ‘OOC1426’ > ‘Lotto’ > ‘SVR 9634’ > ‘OOC 1434’ = ‘OOC 1310’ > ‘Cireo’. Treatment-based color differences were also evident in colorimeter and spectroradiometer readings. Also, panelists differentiated samples grown in 2003 based on red color intensity. Correlations between analytic and instrumented and human panelist-based measures suggest instrumented assessments of red coloration may serve as proxies for direct measures of anthocyanin levels or human panelist ratings, particularly if the aim is to establish color differences between major experimental groups and assign quantitative, repeatable values to red color intensity.

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Low and high tunnels and root-zone heating systems are proven tools in horticultural production. However, impacts of their individual and combined application on crop yield, composition, and microclimates are under-reported. We set out to enhance the record of management strategy effects on abiotic environmental conditions and cropping variables in open field and high-tunnel settings. In each setting, raised bed plots were subsurface heated (underlain by electric heating cables), aerial covered (0.8-mil, clear, vented, low tunnels), subsurface heated and aerial covered, or unheated and uncovered (control). The study was repeated four times in spring and fall seasons across 3 years in Wooster, OH. Red-leaved romaine lettuce (Lactuca sativa ‘Outredgeous’ and ‘Flagship’) was direct seeded in all plots in early October and late March and harvested after ≈4 weeks. Subsurface and aerial temperatures were monitored throughout the experiments. Here, we report primarily on treatment effects on crop microclimate conditions, including temperature and light, and related cropping variables. Subsurface and aerial temperatures varied consistently with plot microenvironment management. Relative to control plots, variability in shoot- and root-zone temperatures generally increased and decreased, respectively, with the addition of low tunnels and electric heating cables, regardless of setting. Still, the relative influence of aerial and soil temperature on crop biomass appeared to differ by setting; aerial temperature correlated most strongly with yield in the high tunnel, while the combination of aerial and root-zone temperature correlated most strongly with yield in the field. Growing degree day accumulation was least in control plots. And, the highest thermal energy to plant biomass conversion efficiency was recorded in the high tunnel. Comparing study-wide and historical climatic data collected in Wooster and other locations in the region suggests that results reported here may hold over a larger area and longer time frame in Wooster, OH.

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Low and high tunnels and root-zone heating systems are proven tools in horticultural production. However, impacts of their separate and combined application on crop yield, composition, and microclimates are underreported. We addressed these gaps in the literature by exposing lettuce (Lactuca sativa) to four microclimates established with low and high tunnels and root-zone heating during the spring and fall of 2 years in Wooster, OH. Red-leaved romaine lettuce cultivars Outredgeous and Flagship were direct-seeded into raised beds in both outdoor and high-tunnel settings in early October and late March and harvested multiple times over 4 weeks. Half of all plots in each setting were underlain by electric heating cables, and half were covered with 0.8-mil, clear, vented, low tunnels. A growing medium consisting of peat moss, compost, soil, and red clover (Trifolium pratense) hay was used, and all plots were overhead-irrigated. Soil and air temperatures were monitored throughout the experiments, which were repeated four times (2 seasons/year × 2 years). Here, we report primarily on treatment effects on crop yield and related variables. Root- and shoot-zone conditions and cultivar significantly affected leaf biomass in both settings (outdoor, high tunnel), while population was more often affected in the outdoor experiments. Microclimate main effects were more prevalent than cultivar effects or interactions. Leaf yield was greater in low-tunnel-covered and bottom-heated plots than in uncovered and unheated plots. We take these data as further evidence of the potential to alter lettuce yield through root- and shoot-zone microclimate modification, particularly in regions prone to dynamic seasonal and within-season temperature and light conditions. The data also suggest that the relative performance of low and high tunnels in the production of short-statured, quick-cycling crops during fall and spring be more thoroughly evaluated.

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