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Beiquan Mou

There is increasing medical evidence for the health benefits derived from dietary intake of carotenoid antioxidants, such as β-carotene and lutein. Enhancing the nutritional levels of vegetables would improve the nutrient intake without requiring an increase in consumption. A breeding program to improve the nutritional quality of lettuce (Lactuca sativa L.) must start with an assessment of the existing genetic variation. To assess the genetic variability in carotenoid contents, 52 genotypes including crisphead, leaf, romaine, butterhead, primitive, Latin, and stem lettuces, and wild species were planted in the field in Salinas, Calif., in the Summer and Fall of 2003 with four replications. Duplicate samples from each plot were analyzed for chlorophyll (a and b), β-carotene, and lutein concentrations by high-performance liquid chromatography (HPLC). Wild accessions (L. serriola L., L. saligna L., L. virosa L., and primitive form) had higher β-carotene and lutein concentrations than cultivated lettuces, mainly due to the lower moisture content of wild lettuces. Among major types of cultivated lettuce, carotenoid concentration followed the order of: green leaf or romaine > red leaf > butterhead > crisphead. There was significant genetic variation in carotenoid concentration within each of these lettuce types. Crisphead lettuce accumulated more lutein than β-carotene, while other lettuce types had more β-carotene than lutein. Carotenoid concentration was higher in summer than in the fall, but was not affected by the position of the plant on the raised bed. Beta-carotene and lutein concentrations were highly correlated, suggesting that their levels could be enhanced simultaneously. Beta-carotene and lutein concentrations were both highly correlated with chlorophyll a, chlorophyll b, and total chlorophyll concentrations, suggesting that carotenoid content could be selected indirectly through chlorophyll or color measurement. These results suggest that genetic improvement of carotenoid levels in lettuce is feasible.

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Bhimanagouda S. Patil, Leonard M. Pike, and Kil Sun Yoo

The aglycone, or free quercetin, and total quercetin content of 75 cultivars and selections was analyzed by reverse-phase high-performance liquid chromatography. Quercetin glycosides were hydrolyzed into aglycones. Total quercetin content in yellow, pink, and red onions varied from 54 to 286 mg·kg-1 fresh weight in different onion entries grown during 1992. White onions contained trace amounts of total quercetin. Free quercetin content in all the onions was low (< 0.4 mg·kg-1) except in `20272-G' (12.5 mg·kg-1 fresh weight). Bulbs stored at 5, 24, and 30C and controlled atmosphere (CA) for 0,1,2,3,4, and 5 months showed a most marked change in total quercetin content at 24C compared to other treatments, with a rise in mid-storage followed by a drop. Storage at 5 and 30C also demonstrated a similar change. However, total quercetin content did not vary significantly in bulbs stored at CA for 5 months. We conclude that genetic and storage factors affect quercetin content on onions.

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J.R. Ballington, W.E. Ballinger, and E.P. Maness

Abstract

HPLC analysis of seven blueberry species, V. ashei Read (2n = 6x = 72), V. constablaei Gray (2n = 6x = 72), V. corymbosum L. (2n = 2X = 24 and 2n = 4X = 48), V. elliotti Chap. (2n = 2X = 24), V. pallidum Ait. (2n = 2X 24 and 2n = 4X = 48), V. simulatum Small (2n = 4X = 48), and V. tenellum Ait. (2n = 2X = 24), identified the 3-monoarabinosides, 3-monogalactosides, and 3-monoglucosides of cyanidin, delphinidin, malvidin, peonidin, and petunidin in each species. Differences in relative percent of individual anthocyanins in some instances were useful in distinguishing among both species and ploidy levels. Differences in percent aglycones were also useful in distinguishing among species. Evidence presented does not support grouping V. elliotti, V. simulatum, and V. constablaei into a single “highbush” species (i.e., V. corymbosum). Percent cyanidin-3-galactoside appeared useful in distinguishing ploidy levels in V. pallidum and between 4X V. pallidum and the “palloid” phase of V. constablaei (6X).

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Kimberly P. Harvell and Paul W. Bosland

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Wansang Lim, Kenneth W. Mudge, and Jin Wook Lee

We determined the effect of moderate water stress on the growth of american ginseng (Panax quinquefolium), and on concentrations of six major ginsenosides (Rg1, Re, Rb1, Rc, Rb2, and Rd). Two-year-old “rootlets” (dormant rhizome and storage root) were cultivated in pots, in a cool greenhouse (18.3 ± 2 °C). Pots were watered either every 5 days (control) or every 10 days (stress), repeatedly for 8 days. Soil volumetric water content was measured during the last 10 days of the experiment for both treatments. Leaf water potential, measured on the last day of the experiment, was -0.43 MPa for the control and -0.83 MPa for the stress treatment. Drought stress did not affect above-ground shoot or root dry weight. Initial rootlet fresh weight (covariate) had a significant effect on the concentration of ginsenosides Re, Rb1, Rc, and Rb2. Drought stress increased the concentration of ginsenosides Re, Rb1, and total ginsenoside concentration.

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Dean A. Kopsell, David E. Kopsell, Mark G. Lefsrud, Joanne Curran-Celentano, and Laura E. Dukach

Green leafy vegetables are important sources of dietary carotenoids, and members of Brassica oleracea L. var. acephala rank highest for reported levels of lutein and β-carotene. Twenty-three leafy B. oleracea cultigens were field grown under similar fertility over two separate years and evaluated for leaf lutein and β-carotene accumulation. Choice of B. oleracea cultigen and year significantly affected carotenoid levels. Lutein concentrations ranged from a high of 13.43 mg per 100 g fresh weight (FW) for B. oleracea var. acephala `Toscano' to a low of 4.84 mg/100 g FW for B. oleracea var. acephala 343-93G1. β-carotene accumulations ranged from a high of 10.00 mg/100 g FW for B. oleracea var. acephala `Toscano' to a low of 3.82 mg/100 g FW for B. oleracea var. acephala 30343-93G1. Carotenoid concentrations were significantly higher in year 2 than in year 1, but rank order among the cultigens for both lutein and ß-carotene did not change between the years. During each year, there were high correlations between leaf carotenoid and chlorophyll pigments. Under similar growing conditions, choice of B. oleracea cultigen will influence carotenoid accumulation, and this may affect the health benefits of consuming these leafy green vegetable crops.

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Mark G. Lefsrud, Dean A. Kopsell, David E. Kopsell, and Joanne Curran-Celentano

Crop plants are adversely affected by a variety of environmental factors, with air temperature being one of the most influential. Plants have developed a number of methods in the adaptation to air temperature variations. However, there is limited research to determine what impact air temperature has on the production of secondary plant compounds, such as carotenoid pigments. Kale (Brassica oleracea L.) and spinach (Spinacia oleracea L.) have high concentrations of lutein and β-carotene carotenoids. The objectives of this study were to determine the effects of different growing air temperatures on plant biomass production and the accumulation of elemental nutrients, lutein, β-carotene, and chlorophyll pigments in the leaves of kale and spinach. Plants were grown in nutrient solutions in growth chambers at air temperatures of 15, 20, 25, and 30 °C for `Winterbor' kale and 10, 15, 20, and 25 °C for `Melody' spinach. Maximum tissue lutein and β-carotene concentration occurred at 30 °C for kale and 10 °C for spinach. Highest carotenoid accumulations were 16.1 and 11.2 mg/100 g fresh mass for lutein and 13.0 and 10.9 mg/100 g fresh mass for β-carotene for the kale and spinach, respectively. Lutein and β-carotene concentration increased linearly with increasing air temperatures for kale, but the same pigments showed a linear decrease in concentration for increasing air temperatures for spinach. Quantifying the effects of air temperature on carotenoid accumulation in kale and spinach, expressed on a fresh mass basis, is important for growers producing these crops for fresh markets.

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Dean A. Kopsell and William M. Randle

Four cultivars of onion (Allium cepa L. `Primavera', `Granex 33', `Pegasus', and `Sweet Success') were grown to maturity in modified nutrient solutions with or without 2.0 mg·L-1 Na2 SeO4 (1.51 mg·L-1 SeO4 -2). Selenium did not affect total flavor precursor content (ACSO) in `Granex 33', `Pegasus', and `Sweet Success'. However, Se affected several individual ACSOs and precursor intermediates. Selenium decreased γ-L-glutamyl-S-(1-propenyl)-L-cysteine sulfoxide and trans(+)-S-(1-propenyl)-L-cysteine sulfoxide content in all four cultivars. (+)-S-Methyl-L-cysteine sulfoxide content was higher while (+)-S-propyl-L-cysteine sulfoxide content was lower with the added Se for two cultivars. Selenium lowered total bulb S content in all cultivars, and increased the percentage of total S accumulated as SO4 -2 in three cultivars. The effect of Se on the flavor pathway was similar to that found when onions were grown under low S-concentrations. Flavor changes can be expected when onions are grown in a high Se environment, however, specific changes may be cultivar dependent.

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N. Georgelis, J.W. Scott, and E.A. Baldwin

Small-fruited cherry tomato accession PI 270248 (Lycopersicon esculentum Mill. var. cerasiforme Dunal) with high fruit sugars was crossed to large-fruited inbred line Fla.7833-1-1-1 (7833) that had normal (low) fruit sugar. Sugars in the F2 were positively correlated with soluble solids, glucose, fructose, pH, and titratable acidity, and inversely correlated with fruit size. Earliness was not significantly correlated with sugars but was negatively correlated with fruit size. Thus, the lack of a sugar-earliness correlation indirectly indicates a trend for early tomato plants to be lower in sugars than later maturing plants. Sugars were not correlated with yield or pedicel type. Fruit from indeterminate plants had significantly more sugars than from determinate plants. Six random amplified polymorphic DNA (RAPD) markers linked to high sugars were found, five dominant (OPAE 4, UBC 731, UBC 744, UBC 489, UBC 290) and one co-dominant (UBC 269). Five of the markers were also linked to small fruit size and one of these also was linked to low yield (UBC 290). The sixth marker (UBC 269) was linked to indeterminate plant habit. UBC 731, UBC 489, and possibly OPAE 4 were in one linkage group, while UBC 744 and UBC 290 were in another linkage group. Combinations of all the markers together explained 35% of the sugar variation in the F2 grown in Spring 2002.