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Jan E.P. Debaene and I.L. Goldman

Raw onion extract contains organosulfur compounds that prevent aggregation of platelets in human blood plasma and influence onion pungency. Organosulfur compounds are volatile and may change concentration during storage. A study was conducted to determine 1) whether antiplatelet activity of filtered onion extract decreases during time in cold (4C) storage; and 2) correlations among antiplatelet activity, pyruvic acid content, and percent solids during time in cold storage. Two low-pungency genotypes (8155 and Exhibition) and two high-pungency (W420 and W434) genotypes were grown in replicated plots in two Wisconsin and two Oregon locations in 1994. Bulbs were evaluated for antiplatelet activity, percent solids, and pyruvic acid content at 40-day intervals after onion harvest. Significant differences were found for pyruvic acid content, solids, and antiplatelet activity among dates of sampling, genotypes, and locations. Mean pyruvic acid concentrations ranged from 6.4 μm·ml–1 of extract for Exhibition, to 8.0 μm·ml–1 of extract for W420. Mean solids concentrations ranged from 5.8 g/100 g for Exhibition to 11.4 g/100 g for W434. Antiplatelet activity averaged over all genotypes increased over 120 days and was positively correlated with percent solids and pyruvic acid content.

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Brian K. Hamilton, Leonard M. Pike, Alton N. Sparks, David A. Bender, and Richard W. Jones

Thrips are the major insect pest of onions grown in South Texas. Four cultivars, `IPA-3', `TG1015Y', `1664' (glossy control), and `1900B' (waxy control), were grown in a split-plot design with insecticide sprayed or nonsprayed treatments as the main plots and cultivar as the subplots. The experiment was conducted at the Texas Agricultural Experiment Station, Weslaco, Texas, in the 1995-96 season. The objectives of the study were to compare `IPA-3' and `TG1015Y' for thrips resistance and evaluate possible resistance mechanisms that may be present in `IPA-3'. The average number of thrips per plant and leaf damage rating were significantly higher for `TG1015Y', indicating that some resistance is present in `IPA-3'. However, there were no significant differences in yield between the two cultivars. A comparison of leaf wax characteristics indicated no significant difference between `TG1015Y' and `IPA-3' using gravimetric or gas chromatography techniques. However, scanning electron micrographs of `TG1015Y' leaves appeared more similar to `1900B' and `IPA-3' appeared more similar to `1664'. The insecticide spray treatment had significantly fewer thrips, less damage, and higher yield than the nonsprayed treatment.

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Jan E.P. Debaene and I.L. Goldman

Onion is a species within the Allium genus with great culinary importance. Onion extract contains organosulfur compounds that influence pungency and inhibit blood platelet aggregation. Antiplatelet activity has the potential of reducing cardiovascular disease. Onions are typically held in postharvest storage for up to 160 days, during which time volatile organosulfur compounds may be affected. A study was conducted to evaluate antiplatelet activity, pungency, and percent solids during cold storage of onions grown in replicated plots in Wisconsin and Oregon in 1994 and 1995. Organosulfur compound concentration and antiplatelet activity were also measured in progeny derived from crosses of inbred lines contrasting for pungency grown during 1995 and 1996 in Wisconsin. For the first study, bulbs were evaluated for antiplatelet activity, percent solids and pungency at 40day intervals after harvest. Significant differences were detected for these traits among years, states, dates of sampling, and lines. During the 120-day postharvest period in 1994, antiplatelet activity increased by 25% and 80% for Oregon and Wisconsin, respectively, averaged over all lines. During the same period in 1995, antiplatelet activity decreased by 35% and 4% in the two locations. For three out of four lines, antiplatelet activity was 4.6% higher for Wisconsin than Oregon. Averaged over states, antiplatelet activity was 9.7% higher in 1994 compared to 1995. Pungency was positively correlated with antiplatelet activity in Wisconsin. Broad-sense heritabilities were calculated for antiplatelet activity and organosulfur compound concentration. These data demonstrate that environmental factors influence postharvest flux of antiplatelet activity and pungency in onion.

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Dean A. Kopsell and William R. Randle

The affects of selenium (Se) on sulfur (S) uptake and metabolism were evaluated in `Granex 33' onions. Plants were grown in a half-strength Hoagland's solution and modified with increasing Se fertility. Selenium was added as sodium selenate. During growth, plants were sampled biweekly and divided into root, bulb, and foliar tissue. Tissues were dried and ground for total S, and wet-ashed for total Se (GFAA). Selenium increased S uptake by onions. As Se increased in concentration, S utilization first increased then decreased in a quadratic trend.

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Kathryn S. Orvis and Irwin L. Goldman

Organosulfur compounds in onion extracts inhibit the aggregation of human blood platelets. Antiplatelet activity is important to human cardiovascular health. We hypothesized that modification of sulfur fertility may increase organosulfur compound concentration and thereby affect platelet inhibitory activity in onion. Four contrasting onion genotypes were grown at four sulfur levels in a hydroponic system in the greenhouse and in contrasting sulfur environments in seven field locations in Wisconsin, Oregon, and New York. The contrasting field sites were comprised of sandy soils with a mean sulfate level of 5.4 ppm and muck soils with a mean sulfate level of 20.3 ppm. Onions grown in field environments with increased soil sulfur concentrations had significantly higher antiplatelet activity (33% higher than sand-grown onions; P < 0.001). The greenhouse experiment was conducted in hydroponics with nutrient solutions containing four sulfur levels ranging from 0.8 mM to 15 mM sulfate. The 10-mM sulfur treatment resulted in onion bulbs with 10% higher antiplatelet activity over those grown in the 0.8-mM sulfur treatment (P < 0.06). These data suggest that sulfur concentration in nutrient solution and in soil may be directly responsible for the increased antiplatelet activity in onion extracts observed in this study.

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C.R. Galmarini, I.L. Goldman, and M.J. Havey

Solid content is an important characteristic related to onion flavor, texture, and storability and has practical importance for the dehydration industry. Among the salutary effects of Allium vegetables on the cardiovascular system is the inhibition of platelet activity. Platelets play a key role in thrombosis and acute coronary syndromes because they facilitate blood coagulation. Pungency is also an important commercial trait. A 138-point genetic map is being used to identify and estimate the magnitude of quantitative trait loci controlling solid content, pungency, and health-enhancing attributes of onion. QTL controlling pungency, total solids, soluble solids, and antiplatelet activity were estimated using 54 F3 families, derived from the cross between Brigham `Yellow Globe 15-23' (BYG15-23) and `Ailsa Craig' (AC43). The families, the two parents, and controls were evaluated in four environments, at Palmyra or Randolph, Wis., during 1997 and 1998, on muck soils. For the analyzed traits there is evidence of trangressive segregation, the distributions are, in general, skewed towards the BYG 15-23 parent. Our results confirmed the existence of strong phenotypic correlations among the traits under study. QTL data available also suggest the existence of significant correlations between markers and the traits under study. Most of the markers that are significant for pungency and antiplatelet activity are also significant for solids, suggesting that these characteristics may be controlled by the same chromosome regions.

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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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Joan Simó, Roser Romero del Castillo, Antoni Almirall, and Francesc Casañas

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Jan E.P. Debaene and I.L. Goldman

Raw onion extract contains organosulfur compounds that prevent aggregation of platelets in human blood plasma and influence onion pungency. An increase in antiplatelet activity has the potential of reducing cardiovascular diseases. Accumulating organosulfur compounds directly influences pyruvic acid concentrations and may determine antiplatelet activity. Organosulfur compounds are volatile and may change concentration during storage. A study was conducted to evaluate antiplatelet activity, pyruvic acid content, and percent solids during cold storage. Two low-pungency lines (8155B and Exhibition) and two high-pungency (W420B and W434B) lines were grown in replicated plots at two Wisconsin locations in 1994 and 1995. Bulbs were evaluated for antiplatelet activity, percent solids, and pyruvic acid content at 40-day intervals after onion harvest. We found significant differences for antiplatelet activity and pyruvic acid content among dates of sampling and lines. Averaged over lines antiplatelet activity increased by 73% and 29% over 160 days in storage during the 1994–95 and 1995–96 storage seasons, respectively. Mean pyruvic acid concentrations increased 27% for the 1994–95 storage season and decreased 27.5% for the 1995–96 storage season. There were no significant changes for solids during storage for both years. These data indicate that antiplatelet activity increases during storage, which may be beneficial for human health. Since onions are often stored for long periods of time before sale, an increase in antiplatelet activity may be an added benefit for this crop.

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Sunggil Kim*, Marla Binzel, Sunghun Park, Kil-Sun Yoo, and Leonard Pike

Anthocyanin, one of the flavonoids, is a primary determinant of red color in onions. Inheritance studies indicate that a single gene determines the color difference between yellow and red onions. In order to establish which gene might be responsible for this color difference, full-length cDNAs of five structural genes: chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), and flavonol synthase (FLS) were cloned using degenerate PCR and RACE (Rapid Amplification of cDNA Ends). RT-PCR was carried out for these five genes to examine differential expression between yellow and red colored bulbs. Accumulation of the DFR gene transcript only occurred in red onions. In F3 populations which originated from the cross between yellow and red parents, DFR transcript was detected only in red F3 lines, not in yellow F3 lines. To design molecular markers for selection of yellow and red DFR alleles, the DFR gene was sequenced from genomic DNA isolated from both types of onions. The genomic DNA sequence revealed the DFR gene consists of six exons and five introns. A PCR-RFLP marker was designed based on 2% polymorphic nucleotide sequence of the DFR gene between yellow and red onions. The co-segregation of markers and red color were observed in F2 segregating populations, supporting the conclusion that color difference in red and yellow onions is likely to be due to the lack of an active DFR gene.