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Laura Avila, Johannes Scholberg, Lincoln Zotarelli, and Robert McSorely

Poor water- and nutrient-holding capacity of sandy soils, combined with intense leaching rainfall events, may result in excessive N-fertilizers losses from vegetable production systems. Three cover cropping (CC) systems were used to assess supplemental N-fertilizer requirements for optimal yields of selected vegetable crops. Fertilizer N-rates were 0, 67, 133, 200, and 267; 0, 131, and 196; and 0, 84, 126,168, and 210 kg N/h for sweet corn (Zea mays var. rugosa), broccoli (Brassica oleracea), and watermelon (Citrullus lanatus), respectively. Crop rotations consisted of sunn hemp (Crotalaria juncea) in Fall 2003 followed by hairy vetch (Vicia villosa), and rye (Secale cereale) intercrop or a fallow. During Spring 2004, all plots were planted with sweet corn, followed by either cowpea (Vigna unguiculata) or pearl millet (Pennisetum glaucum), which preceded a winter broccoli crop. Hairy vetch and rye mix benefited from residual N from a previous SH crop. This cropping system provided a 5.4 Mg/ha yield increment for sweet corn receiving 67 kg N/ha compared to the conventional system. For the 133 N-rate, CC-based systems produced similar yields compared to conventional systems amended with 200 kg N/ha. Pearl millet accumulated 8.8 Mg/ha—but only 69 kg N/ha—and potential yields with this system were 16% lower compared to cowpea system. For a subsequent watermelon crop, trends were reversed, possibly due to a delay in mineralization for pearl millet. Because of its persistent growth after mowing, hairy vetch hampered initial growth and shading also delayed fruit development. Although CC may accumulate up to 131 kg N/ha actual N benefits, N-fertilizer benefits were only 67 kg N/ha, which may be related to a lack of synchronization between N release and actual crop demand.

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Stephanie G. Harvey and Carl E. Sams

Isothiocyanates are volatile chemicals produced by damaged tissues of Brassica species. Allyl isothiocyanate (AITC), the predominant isothiocyanate in Indian mustard (B. juncea), has been shown to control pest in laboratory and field experiments. We investigated the effectiveness of AITC against the germination of sclerotia of Sclerotium rolfsii Saccardo, a common soilborne pathogen of tomato. Sclerotium rolfsii was cultured on PDA from a field isolate. Mature sclerotia were collected and placed in polyester mesh bags. Culture tubes (16 × 150 mm) were packed with 18 g clay loam soil. A sclerotia-bag was placed in each tube and covered with an additional 5 g soil. Soil was maintained at 60% field capacity for the duration of the experiment. AITC was injected into each tube through a septum. Treatments consisted of 0, 5.6, 11.2, 22.4, and 44.8 μmol AITC/L of atmosphere and an ethanol control. AITC in each tube was sampled using SPME and analyzed on GC-MS. Tubes remained sealed for 42 h at 30 °C. Sclerotia were then removed from tubes and bags and plated on PDA to determine viability. Radial growth was measured to determine the effects of AITC. Mycelial growth was negatively correlated to AITC concentration (P < 0.01). The highest concentration of AITC resulted in a 40.3% reduction in mycelial growth. Although the AITC concentrations used in this study did not kill sclerotia of S. rolfsii, they did suppress mycelial growth from germinating sclerotia. At higher concentrations, or mixed with other chemicals, AITC may prove to be an affective control for this pathogen.

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Donald J. Makus* and Gene E. Lester

Field-grown mustard greens, Brassica juncea, were used to validate several observations of a greenhouse study which reported nutrient changes in mustard greens grown, in part, under ambient and reduced light. The cultivar Florida Broadleaf was transplanted into a Hildago sandy clay soil near Weslaco, Texas (26° 08' Lat.) on 6 Nov 2003. Greens were fertigated with 30 kg·ha-1 of N on 1 Dec. Plants 14 days before harvest were grown under the following four light regimes: (1) continuous ambient light; (2) 7 days of 50% shade then 7 days of ambient light; (3) 7 days of ambient light then 7 days of 50% shade; and (4) 14 days of 50% shade. Cumulative solar light was 28.9 and 19.4 kW/m2 during the first and second 7 days, respectively. Measured cumulative light, as PPFD, for treatments 1-4 were 108, 67, 78, and 44 mm·m-2·s-1, respectively. Plants were harvested at 0800, 1100, and 1400 h on 2 Jan. 2004. Shade during the last 7 days generally evoked the greatest responses. Increased shade duration did not significantly effect the agronomic performance, but did increase leaf total carotenoids, chlorophylls, water content, and reduced total ascorbate levels. As time of daylight progressed, sample plant weight and average leaf weight decreased in shaded plants only. Free ascorbic acid, chlorophyll a:b ratio, and the chlorophyll to carotenoid ratio decreased with time of day. Cumulative sunlight, as PPFD, was significantly correlated with total ascorbate (fresh weight basis), chlorophyll a:b ratio, and plant weight (P < 0.06) and negatively correlated with chlorophylls and total carotenoids (dry weight basis). Thus, cloudy weather prior to harvest can reduce leaf Vitamin C and alter leaf greenness

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Victoria J. Ackroyd and Mathieu Ngouajio

the government. Cover crops in the Brassicaceae family (brassica) such as oilseed radish, oriental mustard, and yellow mustard have been shown to decrease plant pathogen populations in the soil ( Sarwar et al., 1998 ). Cover crops in general provide a

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Xinjuan Chen, Zhujun Zhu, Joska Gerendás, and Nadine Zimmermann

(glucosinolates, carotenoids and chlorophylls) and ascorbic acid in selected Brassica species ( B. juncea, B. rapa subsp. nipposinica var. chinoleifera, B. rapa subsp. Chinensis and B. rapa subsp. rapa ) J. App. Bot. Food Qual. 79 168 174

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Aaron Heinrich, Shinji Kawai, and Jim Myers

. However, as a management strategy, growing resistant cultivars has its limitations. For some high-demand crops such as kale ( B. oleracea var. acephala ), mustard greens ( Brassica juncea ), and arugula ( Eruca sativa ), no resistant cultivars are

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Giovanni Antoniaci Caputo, Sandra Branham, and Matthew Cutulle

South Carolina ranked first nationally in the production of collard ( Brassica oleracea var. viridis ) and turnip greens ( Brassica rapa var. rapa L.) greens ( U.S. Department of Agriculture, 2019 ). Weed management for vegetables in the

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Pai-Tsang Chang, Marc W. van Iersel, William M. Randle, and Carl E. Sams

plants to take it up. Among vegetables, Brassica species are good Se deliverers because of their high accumulation of Se; e.g., Indian mustard ( Brassica juncea L.) ( Bañuelos et al., 1997b ) and canola ( Brassica napus L.) ( Bañuelos, 2002 ) are able

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Huan Xiong, Ping Chen, Zhoujun Zhu, Ya Chen, Feng Zou, and Deyi Yuan

genetically stable, is less affected by the environment, and is easy to identify. Petaloid stability is found in many crop species, including Solanum melongena ( Chen et al., 2013 ), Brassica juncea ( Yu et al., 2010 , 2014 ), Daucus carota ( Kozik et

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Gary S. Bañuelos and Bradley D. Hanson

more Se from the soil. Once absorbed by plant roots, Se translocated to the shoot and other plant parts may be harvested and removed from the site. Bañuelos (2002) reported that Brassica crops, e.g., canola ( B. napus ), Indian mustard ( B. juncea