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Richard Parker

Pathogen control is of prime importance in the retail food industry. The Howard E. Butt Grocery Co. (HEB) instituted a testing program for Escherichia coli in 1997. Although not all strains of E. coli are harmful; it was chosen as a test organism because of the ease of assay and it is indicative of the potential presence of other pathogens. By the second quarter of 2000, HEB had reduced percentage of samples with E. coli from 15% to less than 5%. This was done with testing and producer educational programs to improve the safety of produce sold by HEB. Food suppliers to HEB must meet product safety and quality standards. HEB won the International Association for Food Protection's Black Pearl award in 1994, and was the first retailer to integrate hazard analysis and critical control points (HACCP) into their seafood markets. HEB's sampling program helped reduce E. coli levels in sprouts [alfalfa (Medicago sativa), bean (Phaseolus aureus), and radish (Raphanus sativus) sprouts], white mushrooms (Agaricus bisporus), and limes [persian lime (Citrus aurantifolia) and key lime (C. latifolia)], as well as in the prepared product, pico de gallo [a mixture of chopped tomato (Lycopersicon esculentum), pepper (Capsicum annuum), onion (Allium sativa), and cilantro (Coriandrum sativium)]. Incidence of E. coli in lettuce (Lactuca sativa) was related to the season of the year. E. coli levels varied with the crop, but generally better growers had lower E. coli regardless of crop. Country of origin has some effect on the incidence of E. coli, while organic vs. conventional production had little, if any, influence.

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Guangyao Wang, Mathieu Ngouajio and Darryl D. Warncke

The effects of cover crops on nutrient cycling, weed suppression, and onion (Allium cepa) yield were evaluated under a muck soil with high organic matter in Michigan. Four brassica cover crops, including brown mustard (Brassica juncea ‘Common brown’), oilseed radish (Raphanus sativus ‘Daikon’), oriental mustard (B. juncea ‘Forge’), and yellow mustard (Sinapis alba ‘Tilney’), as well as sorghum sudangrass (Sorghum bicolor × S. sudanense ‘Honey Sweet’) produced similar amount of biomass and recycled similar amounts of nitrogen, phosphorus, and potassium. The brassica cover crop biomass contained more calcium, sulfur, and boron, but less magnesium, iron, manganese, copper, and zinc than sorghum sudangrass. However, soil fertility was generally similar regardless of whether a cover crop was used. This was mainly because the soil was sampled when most of the cover crop residue was not yet decomposed. Weed density during onion growth was reduced by all cover crops compared with the control with no cover crop, with yellow mustard treatment having the lowest weed density among the cover crops. Weed species composition was also significantly affected by the cover crops. Yellow mustard treatment had the lowest density of common purslane (Portulaca oleracea) and redroot pigweed (Amaranthus retroflexus), whereas sorghum sudangrass had the highest yellow nutsedge (Cyperus esculentus) density among all the treatments. However, weed suppression was not enough to eliminate normal control strategies. The brassica cover crops, especially oilseed radish and yellow mustard, increased onion stand count and marketable yield. These results suggest that brassica and sorghum sudangrass cover crops could provide multiple benefits if incorporated into short-term onion rotations under Michigan growing conditions.

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Victoria J. Ackroyd and Mathieu Ngouajio

Field and laboratory bioassay studies were conducted to determine the impact of Brassicaceae cover crops on cucurbit germination percentages and stand counts. A 2-year field study in southwestern Michigan examined the effect of oilseed radish (Raphanus sativus var. oleiferus), oriental mustard (Brassica juncea), and yellow mustard (Sinapis alba) green manures on muskmelon (Cucumis melo Group reticulatus) stand. All three cover crops reduced direct-seeded muskmelon stand count as well as transplant survival. Stand count for direct- seeded muskmelon was greater than 85% for control and methyl bromide treatments and less than 41% for cover crop treatments. Oilseed radish had the greatest effect with 0% muskmelon stand in both years. The use of transplants improved muskmelon stand establishment. However, stand count (less than 45% to 50%) was still unacceptable. In bioassays, muskmelon, cucumber (Cucumis sativus), and honeydew melon (Cucumis melo Group inodorus) seeds were exposed to either non-lyophilized or lyophilized root and shoot aqueous extracts of oilseed radish. Germination percentages and radicle elongation measurements showed both extracts impacted all three crops to varying degrees. Muskmelon germination was least sensitive to the extracts, followed by cucumber, then honeydew. Cucumber and muskmelon root growth was equally inhibited by non-lyophilized shoot extract, while honeydew growth was mildly stimulated at 5% and 12.5% concentrations. Overall, non-lyophilized root extract showed stronger inhibition on seed germination than non-lyophilized shoot extract, while the reverse was true of lyophilized extracts. In general, non-lyophilized extracts had far greater impact on germination percentages and radicle elongation than lyophilized extracts. These results suggest species and tissue dependent toxicity of the cover crops as well as differential susceptibility of the cucurbit crops tested. Therefore, a plant-back period longer than the 8 days used in this study should be observed after cover crop incorporation before cucurbit seeding or transplanting.

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R.M. Wheeler, C.L. Mackowiak, N.C. Yorio, L.M. Ruffe and G.W. Stutte

Radish (Raphanus sativus cv. Giant White Globe) and lettuce (Lactuca sativa cv. Waldmann's Green) plants were grown for 25 days in growth chambers at 23 °C, ≈300 μmol·m-2·s-1 PPF, and 18/6 photoperiod, and four CO2 concentrations: 400, 1000, 5000, and 10,000 μmol·mol-1. Average total dry mass (g/plant) at the 400, 1000, 5000 and 10,000 μmol·mol-1 treatments were 6.4, 7.2, 5.9, and 5.0 for radish and 4.2, 6.2, 6.6, and 4.0 for lettuce. Each species showed an expected increase in yield as CO2 was elevated from 400 to 1000 μmol·mol-1, but super-elevating the CO2 to 10,000 μmol·mol-1 resulted in suboptimal growth. In addition, many radish leaves showed necrotic lesions at 10,000 μmol·mol-1 by 17 days and at 5000 μmol·mol-1 by 20 days. These results are consistent with preliminary tests in which radish cvs. Cherry Belle, Giant White Globe, and Early Scarlet Globe were grown for 16 days at 400, 1000, 5000, and 10,000 μmol·mol-1. In that study, `Giant White Globe' produced the greatest total dry mass at 1000 (3.0 g/plant) and 5000 μmol·mol-1 (3.0 g/plant), and the least at 10,000 μmol·mol-1 (2.2 g/plant). `Early Scarlet Globe' followed a similar trend, but `Cherry Belle' showed little difference among CO2 treatments. Results suggest that super-elevated CO2 can depress growth of some species, and that sensitivities can vary among genotypes.

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T.G. Boucounis, T. Whitwell and J.E. Toler

Ten crops were evaluated for potential use as field bioassay species for cinmethylin and chlorimuron application rates in two soil types. Cinmethylin injured sweet corn (Zea mays L.) and grain sorghum [Sorghum bicolor (L.) Moench] at concentrations as low as 0.28 kg·ha-1 on either soil type, while broadleaf crops were tolerant. Chlorimuron injured sweet corn, grain sorghum, radish (Raphanus sativus L.), cucumber (Cucumis sativus L.), and watermelon [Citrullis lanatus (Thunb.) Mansf.] at rates ≥ 2.5 g·ha-1, and squash (Cucurbita pepo L.) at rates ≥ 5.0 g·ha-1 on a Dothan sand. In a Congaree silt loam, chlorimuron injured cucumber at rates ≥ 5.0 g·ha-1, sweet corn, watermelon, and squash at rates ≥ 10 g·ha-1, and grain sorghum, radish, and cotton (Gossypium hirsutum L.) at rates ≥ 20 g·ha-1. Soybean and snapbean (Phaseolus vulgaris L.) were tolerant to chlorimuron in both soil types. Cinmethylin activity was not altered by soil type, but with chlorimuron greater crop injury was observed in the Dothan sand than in the Congaree silt loam. Sweet corn and grain sorghum were the most sensitive indicator species to cinmethylin and cucumber was the most sensitive to chlorimuron in both soils. Plant emergence and population alone are not valid indicators for crop tolerance to herbicides. Quantitative measurements such as shoot dry weight were more indicative of crop susceptibility to chlorimuron than plant populations. Chemical names used: exo -1-methyl-4-(1-methylethyl)-2 -[(2-methylphenyl) methoxy]-7-oxabicyclo[2.2.1]heptane (cinmethylin); 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino] carbonyl]amino] sulfonyl]benzoic acid (chlorimuron).

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Mitchell Eicher-Sodo, Robert Gordon and Youbin Zheng

Hydrogen peroxide (H2O2) is an oxidizing agent used to disinfect recirculated irrigation water during the production of organic crops under controlled environmental systems (e.g., greenhouses). To characterize the phytotoxic effects and define a concentration threshold for H2O2, three microgreen species [arugula (Brassica eruca ssp. sativa), radish (Raphanus sativus), and sunflower (Helianthus annuus ‘Black Oil’)], and three lettuce (Lactuca sativa) cultivars, Othilie, Xandra, and Rouxai, were foliar sprayed once daily with water containing 0, 25, 50, 75, 100, 125, 150, or 200 mg·L−1 of H2O2 from seed to harvest under greenhouse conditions. Leaf damage was assessed at harvest using two distinct methods: 1) the percentage of damaged leaves per tray and 2) a damage index (DI). Applied H2O2 concentrations, starting from 25 mg·L−1, increased the percentage of damaged leaves in every species except ‘Black Oil’ sunflower, which remained unaffected by any applied concentration. Symptoms of leaf damage manifested in similar patterns on the surface of microgreen cotyledons and lettuce leaves, while mean DI values and extent of damage were unique to each crop. Fresh weight, dry weight, and leaf area of all crops were not significantly affected by daily H2O2 spray. Identifying how foliar H2O2 damage manifests throughout the crop, as well at individual cotyledon or leaf surfaces, is necessary to establish an upper concentration threshold for H2O2 use. On the basis of the aforementioned metrics, maximum recommended concentrations were 150 mg·L−1 (radish), 100 mg·L−1 (arugula) for microgreens and 125 mg·L−1 (‘Othilie’), 75 mg·L−1 (‘Rouxai’), and 125 mg·L−1 (‘Xandra’) lettuce.

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Brent Tisserat, Christopher Herman, Robert Silman and Rodney J. Bothast

A continuous CO2 flow system was used to study the growth of carrot (Daucus carota L.), citrus (Citrus macrophylla L.), kale (Brassica oleracea L.), lettuce (Lactuca sativa L.), radish (Raphanus sativus L.), and tomato (Lycopersicum esculentum L.) cultures in vitro under photoautotrophic, photomixotrophic, and heterotrophic conditions. Lettuce plantlets were grown on Murashige and Skoog medium with 0%, 0.3%, 1%, and 3% sucrose within flow chambers containing 350, 750, 1500, 3000, 10,000, 30,000, and 50,000 μL·L−1 CO2. Increasing the levels of CO2, especially at the ultra-high levels (i.e., ≥3,000 μL·L−1 CO2), increased fresh weight, shoot length, leaf number, leaf length, leaf width, root number, and root length for plantlets grown regardless of sucrose levels tested compared to plantlets grown at normal atmospheric CO2 levels, i.e., 350 μL·L-1. For example, fresh weights of lettuce plantlets grown on medium containing 0% or 3% sucrose increased 11- and 13-fold, respectively, when supplemented with 30,000 μL·L-1 CO2 compared to growth of lettuce plantlets grown on the same media without CO2 enrichment. Similar fold increases in growth responses were obtained with carrot, citrus, kale, radish, and tomato plantlets grown in atmospheres enriched with high CO2 levels, elevated from 3000 to 30,000 μL·L-1. Optimum CO2 concentration varied among species, suggesting a species-related response. Varying the rate of CO2 application between 250, 500, 1500, or 2000 mL·min-1 did not effect the rate of growth of lettuce plantlets. The passive diffusion continuous flow-through system presented in this paper is inexpensive, easily constructed, and allows for testing ultra-high CO2 levels on plant culture growth in vitro.

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Kalpana K.C. Adhikari, Mary Ruth McDonald and Bruce D. Gossen

. rapa atrazine resistant, and Raphanus sativus L. (radish). The RCBC lines were selected to represent the six most economically important and widely grown Brassica crops. The three lines of B. rapa were included because some of the phenotype

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James P. Gilreath and Bielinski M. Santos

nutsedges. In bell pepper ( Capsicum annuum ), radish ( Raphanus sativus ), and cilantro ( Coriandrum sativum ), marketable yield losses reached 73%, 100%, and 61%, respectively, due to intense nutsedge interference ( Gilreath et al., 2005 ; Morales

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Bielinski M. Santos, James P. Gilreath and Myriam N. Siham

. Previous research has indicated that nutsedge interference can reduce bell pepper ( Capsicum annuum ), tomato ( Lycopersicon esculentum ), radish ( Raphanus sativus ), and cilantro ( Coriandrum sativum ) yields by 22%, 51%, 100%, and 61%, respectively