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Theodore J.K. Radovich, Matthew D. Kleinhenz and John G. Streeter

To better understand the influence of environmental factors on components of crop productivity and nutritional and sensory quality parameters, the fresh-market cabbage (Brassica oleracea L. Capitata Group) `Bravo' was irrigated at different periods relative to head development in 2002 and 2003 at the Ohio Agricultural Research and Development Center in Wooster. Irrigation was provided to plots either: 1) from planting to maturity, 2) during frame development only, or 3) during head development only. Control plants received no irrigation after plant establishment. Irrigation timing relative to crop stage significantly affected all head characteristics with the greatest differences between cabbage receiving irrigation during head development and cabbage not irrigated during head development. On average, heads from cabbage irrigated during head development were heavier, larger, less pointed, and had less volume occupied by the core than heads from cabbage not irrigated during head development. A positive, linear relationship (r 2 = 0.89) was found between head volume and head weight. Across years, combined head fructose and glucose concentrations were significantly greater and sucrose concentrations significantly lower in cabbage receiving irrigation during head development than in cabbage not irrigated during head development. Total and individual glucosinolate levels were greater in cabbage not irrigated during head development relative to cabbage receiving irrigation during head development. Head weight, fructose and glucose were positively related to the proportion of estimated crop evapotranspiration replaced by irrigation during head development, while the opposite response was observed in head sucrose and total and indole glucosinolate concentrations.

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Aparna Gazula*, Matthew D. Kleinhenz, Joseph C. Scheerens, Peter P. Ling and John G. Streeter

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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Aparna Gazula*, Matthew D. Kleinhenz, Joseph C. Scheerens, Peter P. Ling and John G. Streeter

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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Aparna Gazula, Matthew D. Kleinhenz, John G. Streeter and A. Raymond Miller

Pigment concentrations in leaf tissue affect the visual and nutritional value-based indices of lettuce crop quality. To better discern the independent and interactive effects of temperature and cultivar on anthocyanin and chlorophyll b concentrations, three closely related Lolla Rosso lettuce cultivars (`Lotto', `Valeria', and `Impuls'), varying primarily in the number of genes controlling anthocyanin concentrations, were subjected to different air temperatures in controlled environments. Fifteen-day-old seedlings previously grown at 20 °C day/night (D/N) were transplanted into growth chambers maintained at 20 °C (D/N), 30/20 °C D/N and 30 °C D/N air temperatures. Twenty days later, leaf tissue was sampled for measures of pigment concentrations, calculated based on spectrophotometric absorbance readings taken at 530 nm (anthocyanin) and 660 nm (chlorophyll b) respectively. Although significant, the temperature × cultivar interaction resulted from differences in the magnitude (not direction) of the change in pigment concentrations among cultivars with changes in temperature. Regardless of cultivar, anthocyanin and chlorophyll b concentrations were highest, moderate and lowest after growth at 20 °C D/N, 30/20 °C D/N and 30 °C D/N respectively. Likewise, irrespective of temperature, anthocyanin and chlorophyll b concentrations followed the pattern `Impuls' (three genes) > `Valeria' (two genes) > `Lotto' (one gene). These data provide additional strong evidence that lettuce leaf pigment concentrations and growing temperatures are negatively related. The data also suggest that low temperatures during the dark phase may mitigate high temperature-driven reductions in lettuce leaf pigment levels.

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Theodore J.K. Radovich, Matthew D. Kleinhenz, John G. Streeter, A. Raymond Miller and Joseph C. Scheerens

Glucosinolates are secondary plant metabolites derived from amino acids and they influence human health, pest populations and crop flavor. Our primary objective was to determine the independent and interactive effects of planting date (PD) and cultivar (C) on total glucosinolate concentrations in cabbage, in part to help develop management systems that optimize them. A second objective was to explore the reported link between total glucosinolate concentrations and pungency in fresh cabbage. Six commercial fresh market cabbage cultivars were planted in May and June 2001 and 2002 at the Ohio Agricultural Research and Development Center (OARDC) Vegetable Crops Research Branch in Fremont, Ohio. Total glucosinolate concentrations in horticulturally mature heads were determined using a glucose evolution procedure. In 2001, 12 to 14 experienced panelists also scored sample pungency. Total glucosinolate concentrations were significantly affected by PD and C, but the PD × C interaction was not significant. Mean glucosinolate concentrations were greater in Maythan June-planted cabbage in both years. Cultivar ranking with regard to glucosinolate concentrations was similar between planting dates in both years. `Cheers' had the highest mean glucosinolate concentrations (23.1 and 29.5 mmol·kg-1 dry weight in 2001 and 2002, respectively) and `Solid Blue 790' the lowest (17.1 and 19.7 mmol·kg-1 dry weight in 2001 and 2002, respectively). In 2001, panelists generally scored cultivars highest in glucosinolates as more pungent than cultivars lowest in glucosinolates. These data suggest that planting date and cultivar effects on total glucosinolate concentrations in cabbage are largely independent. Climatic data suggest that higher air temperatures during head development of May-compared to June-planted cabbage induced plant stress and resulted in higher glucosinolate concentrations in May-planted cabbage.