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Christopher J. D’Angelo and Irwin L. Goldman

Long-day storage onion bulbs (Allium cepa) undergo a period of endodormancy that begins before harvest and lasts for several weeks, depending on the genotype. Onion seed production relies on cold treatment to break endodormancy and vernalize the bulbs. When bulbs are planted shortly after harvest, endodormancy results in delayed growth and, in turn, slower flowering and seed production. Through this work we sought to explore the use of hydrogen peroxide as a treatment to break dormancy in onion bulbs. Endodormant bulbs of two long-day cultivars, Cortland and Sherman, were treated with hydrogen peroxide solutions at various concentrations in a series of experiments over a 3-year period and were monitored for root and leaf (sprout) development. We found a 2- to 4-hour exogenous treatment of 20% (weight by volume) hydrogen peroxide to be highly effective at initiating uniform root growth in endodormant bulbs. When compared with a purified water control, the 20% treatment resulted in a 61.3% average reduction in the time to rooting in 2016. We also observed improved uniformity in rooting time between ‘Cortland’ and ‘Sherman’ in all 3 years of this work. We propose this novel method as a tool for breeders, researchers, and seed producers seeking rapid, uniform endodormancy release in onion bulbs to hasten seed production.

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Christopher J. D’Angelo and Irwin L. Goldman

Vernalization is an important step for floral initiation in onion (Allium cepa), but our understanding of the minimum vernalization time for long-day storage onions to gain floral competence is limited. A series of time course experiments were conducted over 4 years to determine the effects of vernalization time on sprouting, scape emergence, and flowering in ‘Cortland’, ‘Sherman’, and CUDH2107. We found an endodormancy period is present in the bulbs of these cultivars that lasts for 8 to 10 weeks. In addition, these three accessions achieve optimum uniform scape emergence after chilling for 14 weeks at 10 °C. On average, when bulbs were chilled for 14 weeks, it took 96.8 ± 15.6 days from planting to flowering in all accessions evaluated. As storage duration under vernalizing temperatures increases, the time to sprouting, scape emergence, and flowering decrease. Furthermore, the variance in time from sprouting to scape emergence was greatly reduced between 10 and 12 weeks of storage for ‘Cortland’ and CUDH2107, and between 12 and 14 weeks for ‘Sherman’. After 10 weeks of chilling, each additional week of storage resulted in an average decrease in time to flowering of 4.1%. We also observed large percentages of bulbs flowering without receiving any vernalization. This observation supports our finding that the relationship between vernalization and flowering in long-day storage onion is facultative rather than obligate. These findings help define the relationship between dormancy, vernalization, and flowering in long-day storage onion.

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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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Kathryn S. Orvis and Irwin L. Goldman

Heart attack and stroke, a leading cause of death in the United States, have been associated with blood platelet aggregation. Onion extract inhibits blood platelet aggregation both in vitro and in vivo. Current trends toward natural foods and health remedies may point to the importance of onion-induced antiplatelet activity (OIAA). The genetic control of OIAA has yet to be revealed. One-hundred-eighty-three F3 families were derived from a long-day mild inbred line crossed to a long-day pungent inbred line that differ by for OIAA by 67%. Families were grown in a RCB design with two replications in muck soil (Randolph, Wis.) in 1997. Extracts were made from crushing bulb tissue in a mechanical juicer. F3 families were evaluated for OIAA and soluble solids (SS). OIAA was measured by electrical impedance aggregometry using two human blood donors. Endpoint (ohms) and slope of the aggregation curve were recorded. SS were measured by refractometry. F3 families were significantly different for OIAA and SS (P < 0.0001) in the ANOVA. A strong positive correlation of 0.96 was revealed for slope of curve and endpoint across families, replications, and blood donors. This correlation has not been previously reported for onion and suggests that for these families, descriptions of OIAA based on either rate of aggregation or endpoint are functionally equivalent. Both SS and OIAA exhibit transgressive segregation in this group of F3 families. Twenty percent exhibit OIAA stronger than the pungent parent and 5% were less than the mild parent. The family with the highest OIAA was 4-fold higher than the pungent parent of the cross, which could be useful in future onion breeding efforts. In addition, transgressive segregation in these families aids in QTL investigations for OIAA, SS and other economically important traits.

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Amy K. Freidig and Irwin L. Goldman

Oxalic acid (C2O4 2–) is a compound of interest as a result of its relationship with kidney stone formation and antinutritive properties. Because table beet [Beta vulgaris ssp. vulgaris (garden beet group)] is considered a high oxalate food, breeding to decrease oxalic acid levels is an area of interest. In this study, a field trial was conducted over 2 years for 24 members of the Chenopodiaceae using two different planting dates to determine if variation exists for both total and soluble oxalic acid levels in roots and leaves. Total and soluble oxalic acid was extracted from homogenized root core and leaf tissue samples and a colorimetric enzymatic assay was used to determine total and soluble oxalic acid levels. Mean values ranged from 722 to 1909 mg/100 g leaf tissue and 553 to 1679 mg/100 g leaf tissue for total and soluble oxalate levels, respectively. Beet cultivar Forono and swiss chard [B. vulgaris ssp. vulgaris (leaf beet group)] cultivar Burpee's Fordhook Giant Chard produced the respective highest and lowest soluble and total oxalic acid leaf levels. Swiss chard cultivars produced 38% less total oxalate compared with table beet cultivars based on overall means. Root soluble oxalate values ranged from 103 to 171 mg/100 g root tissue and total values ranged from 95 to 142 mg/100 g root tissue. Significant variation for both total and soluble oxalic acid levels were detected, indicating progress could be made toward breeding for lower oxalic acid levels in table beet. However, gains in oxalic acid nutritional quality may be limited because it would take a substantial decrease in levels for table beet to be reclassified as a low oxalate food.

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Marilyn H.Y. Hovius and Irwin L. Goldman

Breeders have found field screening for onion white rot resistance to be unreliable since consistently moderate to high disease levels that significantly differentiate cultivars, do not occur over field sites and years. The objective was to see if a greenhouse or laboratory technique could predict field reaction of onion accessions. Onion (Allium cepa) accessions were grown in fields naturally infested with the white rot causing fungus (Sclerotium cepivorum) in 1999 and 2000 (New Zealand) and in 2000 and 2001 (Canada). The field disease levels were low at three sites, moderate at two and high at one. Field screening was not a reliable predictor of white rot reaction when disease incidence was low. Onion accessions were screened for resistance in the greenhouse using nonsterile muck soil (NSMS) and sterile muck soil (SMS) with S. cepivorum sclerotia as the inoculum source. Total disease incidence was significantly higher in the NSMS compared to the SMS and accessions showed significant variability for white rot reaction in both soils. Two laboratory-based techniques were used to test the effect of onion volatiles on mycelium growth in culture. The volatiles from susceptible accessions resulted in faster radial growth of S. cepivorum mycelium (on water agar) and height of aerial mycelium (on potato dextrose agar) than volatiles from resistant accessions. Disease incidence in the greenhouse, S. cepivorum culture growth rates on water agar media and aerial mycelial height were all good predictors of field disease incidence in a covariance analysis. The best predictor was aerial mycelial height, which was predictive of field disease incidence in four out of six field sites. Onion breeders can use the methods described in this study in breeding for white rot resistance.

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Marilyn H.Y. Hovius, Irwin L. Goldman, and Kirk L. Parkin

Breeders have found field screening for white rot (Sclerotium cepivorum Berk.) resistance in onion (Allium cepa L.) to be unreliable since consistently moderate to high disease levels that significantly differentiate cultivars do not occur over field sites and years. The objective was to determine if differences in onion white rot resistance levels were associated with differing S-alk(en)yl-l-cysteine sulfoxide (ACSO) levels. A collection of onion breeding lines and hybrids were evaluated in field trials at six sites in 1999-2001. High performance liquid chromatography was used to analyze ACSOs in onion plant organs. Four main cysteine-sulfoxides exist in Allium L. species: methyl (MCSO), 2-propenyl (2-PeCSO), 1-propenyl (1-PeCSO), and propyl (PCSO). 1-PeCSO was predominant in onion leaves, bulbs, and roots. 2-PeCSO was found in trace amounts in onion leaves and roots. There was significantly more 2-PeCSO and total ACSO (roots only) and 1-PeCSO (roots and bulbs) in accessions that were more susceptible to white rot in the field trials. This is the first report of significant differences in ACSO contents among white rot susceptible and resistant onions. A covariance analysis was used to determine if the ACSO levels that significantly distinguished among accessions could predict field onion white rot reaction. 1-PeCSO from both roots and bulbs was the best predictor of field disease incidence in field sites that had low, moderate, and high disease levels. Although the ACSO concentrations were not assessed on an individual plant basis, breeders may be able to screen onions for resistance to S. cepivorum by comparing onion root or bulb 1-PeCSO levels based on the results from this research. White rot incidence in the field should be higher in those plants whose roots and bulbs have the highest levels of 1-PeCSO.

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Jennifer L. Baeten, Thomas C. Koch, and Irwin L. Goldman

Carrot has been bred for increased levels of pro-vitamin E α-tocopherol. This vitamin is lipid soluble. Carrot root has been shown to have measurable levels of lipid, but it is not certain if the lipid level is correlated to α-tocopherol levels. The HPLC method is needed to quantify levels of α-tocopherol. Measuring lipids may be less time consuming in a breeding program. We developed a method for extracting lipids from carrot tissue based on the Soxhlet extraction method. The Soxhlet extraction uses a non-polar ether solvent to pull lipids out of freeze-dried tissue. A collection of carrot accessions ranging in α-tocopherol concentration 0.04–0.18 ppm and carotenoid concentration 10.63–1673.76 ppm were used in this investigation. Root tissue was freeze-dried and lipid levels were measured in an experiment with two replications. The mean lipid level of root tissue was 0.05 g fat/g tissue. The range was 0–1.1 g fat/g tissue. Phenotypic correlations were performed among lipid, α-tocopherol, and β-carotene concentrations in these samples. Twenty-four samples were tested for lipid levels (12 high and 12 low). From these results, percent lipid of the root was determined. Correlations were made between the lipid data and α-tocopherol data of the given samples.

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Claire H. Luby, Rachael Vernon, Hiroshi A. Maeda, and Irwin L. Goldman

Vitamin E compounds, known collectively as tocochromanols, are essential nutrients found in plant tissues. These compounds are present in fruits and vegetables at lower levels than in nuts and oils. However, since fruits and vegetables are frequently consumed in the diet, they represent important contributions to vitamin E intake. Knowledge of nutrient levels in fruits and vegetables is important in making dietary recommendations and in planning menus. The U.S. Department of Agriculture (USDA) National Nutrient Database (NNB) reports levels of vitamin E in carrot of 6.6 µg·g−1 on a fresh weight basis and similar levels of vitamin E for food products containing carrots, such as baby food and carrot juice. We collected data on four tocochromanol compounds using reverse-phase high-performance liquid chromatography (HPLC) with fluorescence detection on both fresh carrots and on commercially available food products containing carrots. Our data revealed that levels of vitamin E in fresh carrot and food products containing carrot were in the range of 0.007–0.12 µg·g−1 converted to a fresh weight basis. These levels were consistent with several published research studies for carrot, lower than several other published studies, and significantly lower than values reported in the NNB. Data from our studies show actual vitamin E values for this vegetable may be significantly lower than levels published in the NNB, but large discrepancies exist in the published reports for measurement of tocochromanol levels for this vegetable. Dietary guidance based on vitamin E values for carrot reported in the NNB could lead to inaccurate nutrient recommendations and should be clarified and standardized.