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Dean A. Kopsell and Carl E. Sams

Microgreens are specialty leafy crops harvested just above the roots after the first true leaves have emerged and are consumed fresh. Broccoli (Brassica oleacea var. italica) microgreens can accumulate significant concentrations of cancer-fighting glucosinolates as well as being a rich source of other antioxidant phytochemicals. Light-emitting diodes (LEDs) now provide the ability to measure impacts of narrow-band wavelengths of light on seedling physiology. The carotenoid zeaxanthin has been hypothesized to be a blue light receptor in plant physiology. The objective of this study was to measure the impact of short-duration blue light on phytochemical compounds, which impart the nutritional quality of sprouting broccoli microgreens. Broccoli microgreens were grown in a controlled environment under LEDs using growing pads. Seeds were cultured on the pads submerged in deionized water and grown under a 24-hour photoperiod using red (627 nm)/blue (470 nm) LEDs (350 μmol·m−2·s−1) at an air temperature of 23 °C. On emergence of the first true leaf, a complete nutrient solution with 42 mg·L−1 of nitrogen (N) was used to submerge the growing pads. At 13 days after sowing, broccoli plantlets were grown under either: 1) red and blue LED light (350 μmol·m−2·s−1); or 2) blue LED light (41 μmol·m−2·s−1) treatments for 5 days before harvest. The experiment was repeated three times. Frozen shoot tissues were freeze-dried and measured for carotenoids, chlorophylls, glucosinolates, and mineral elements. Comparing the two LED light treatments revealed the short-duration blue LED treatment before harvest significantly increased shoot tissue β-carotene (P ≤ 0.05), violaxanthin (P ≤ 0.01), total xanthophyll cycle pigments (P ≤ 0.05), glucoraphanin (P ≤ 0.05), epiprogoitrin (P ≤ 0.05), aliphatic glucosinolates (P ≤ 0.05), essential micronutrients of copper (Cu) (P = 0.02), iron (Fe) (P ≤ 0.01), boron (B), manganese (Mn), molybdenum (Mo), sodium (Na), zinc (Zn) (P ≤ 0.001), and the essential macronutrients of calcium (Ca), phosphorus (P), potassium (K), magnesium (Mg), and sulfur (S) (P ≤ 0.001). Results demonstrate management of LED lighting technology through preharvest, short-duration blue light acted to increase important phytochemical compounds influencing the nutritional value of broccoli microgreens.

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Craig S. Charron and Carl E. Sams

The U.S. Clean Air Act bans the use of methyl bromide after 2005. Consequently, the development of alternative methods for control of soilborne pathogens is imperative. One alternative is to exploit the pesticidal properties of Brassica L. species. Macerated leaves (10 g) from `Premium Crop' broccoli [B. oleracea L. (Botrytis Group)], `Charmant' cabbage [B. oleracea L. (Capitata Group)], `Michihili Jade Pagoda' Chinese cabbage [B. rapa L. (Pekinensis Group)], `Blue Scotch Curled' kale [B. oleracea L. (Acephala Group)], Indian mustard [B. juncea (L.) Czerniak, unknown cultivar] or `Florida Broadleaf' mustard [B. juncea (L.) Czerniak] were placed in 500-mL glass jars. Petri dishes with either Pythium ultimum Trow or Rhizoctonia solani Kühn plugs on potato-dextrose agar were placed over the jar mouths. Radial growth of both fungi was suppressed most by Indian mustard. Volatiles were collected by solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry. Allyl isothiocyanate (AITC) comprised >90% of the volatiles measured from `Florida Broadleaf' mustard and Indian mustard whereas (Z)-3-hexenyl acetate was the predominant compound emitted by the other species. Isothiocyanates were not detected by SPME from `Premium Crop' broccoli and `Blue Scotch Curled' kale although glucosinolates were found in freeze-dried leaves of all species. When exposed to AITC standard, P. ultimum growth was partially suppressed by 1.1 μmol·L-1 (μmol AITC/headspace volume) and completely suppressed by 2.2 μmol·L-1 R. solani was partially suppressed by 1.1, 2.2, and 3.3 μmol·L-1 AITC. Use of Brassica species for control of fungal pathogens is promising; the presence of AITC in both lines of B. juncea suppressed P. ultimum and R. solani but some Brassicas were inhibitory even when isothiocyanates were not detected.

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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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Craig S. Charron and Carl E. Sams

There has been significant interest in the glucosinolate-myrosinase system in plants of the Brassicaceae due to accumulating evidence that some glucosinolate degradation products are anticarcinogenic and/or suppressive to plant pathogens. Because glucosinolate hydrolysis is catalyzed by endogenous myrosinase, characterization of myrosinase activity is important for elucidating the potential bioactivity of crop glucosinolates. We measured the specific activity in citrate-phosphate buffer extracts across the pH range 4.5–6.5 of two cultivars each of five Brassica groups grown during two fall and two spring seasons. Specific activity in two kale cultivars was highly variable, but tended to have highest activity from pH 5.0–6.0. In both cauliflower cultivars from Fall 2000, Fall 2001, and Spring 2002, optimal pH was around pH 6.0. In Spring 2000, however, specific activity was highest at pH 5.0. Maximum specific activity in both cabbage cultivars occurred in the pH range 5.5–6.0 in Fall 2000, Fall 2001, and Spring 2002. In Spring 2000, specific activity in `Red Acre' cabbage was uniform across the range pH 4.5–5.5 and maximum specific activity was at pH 5.0 for `Early Round Dutch' cabbage. Both brussels sprouts cultivars had pH maxima around pH 5.5–6.0 and significantly lower activity at pH 4.5. Specific activity in broccoli was much like that of cauliflower in that highest activity occurred around pH 5.5–6.0 in Fall 2000, Fall 2001, and Spring 2002, but in Spring 2000, maximum activity was at pH 5.0. These results indicate that in most cases, pH optima were in the range 5.5–6.0, but varied somewhat with season and genotype.

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Craig S. Charron and Carl E. Sams

Crops of the Brassicaceae contain glucosinolates(GSs), which when hydrolyzed by the enzyme myrosinase, generate products involved in cancer chemoprotection, plant defense, and plant-insect interactions. A rapid-cycling base population of B. oleracea L. was grown in a hydroponic system in a controlled environment to determine the roles of temperature, photosynthetic photon flux (PPF), and photoperiod in GS concentration and myrosinase activity. The concentration of total GSs in leaves was 44% and 114% higher at 12 and 32 °C respectively than at 22 °C under constant light of 300 μmol·m-2·s-1. The concentration of glucoraphanin, the precursor to sulforaphane, a compound with chemoprotective properties, was 5-fold higher at 32 than at 22 °C. Total GSs were ≈50% lower in roots at 12 °C and 32 than at 22 °C. Total GSs in leaves decreased 20% when PPF was increased from 200 to 400 μmol·m-2·s-1. Myrosinase activity on a fresh weight basis (activity-FW) was ≈30% higher in leaves and stems at 12 and 32 °C than at 22 °C, and ≈30% higher in leaves grown at 200 and 400 μmol·m-2·s-1 than at 300 μmol·m-2·s-1. Consideration of climatic factors that influence the glucosinolate-myrosinase system may be necessary to optimize the planting and cultivation of Brassica crops for maximum health benefits.

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Adriane Cannon*, Dennis Deyton, Carl Sams and William Klingeman

Two experiments were conducted in a greenhouse to evaluate soy-bean oil (SO) formulations for effects on powdery mildew (PM) and photosynthesis of dogwood trees. In the first experiment, one-year-old potted trees were sprayed with different formulations of 2% SO one day before exposure to PM. The formulations were emulsified with: teric/termul, lauriciden, lecithin, lecithin/MD 1, lecithin/MD 2, or Latron B-1956. A commercial formulation of Golden Natur'l was also used. The trees were arranged in a completely randomized design with six replications and eight treatments. In the second experiment, trees were sprayed 4 days after initial exposure to PM with the same treatments and arranged in a similar experimental design. The severity of PM infection was rated using the scale: 1 = 0%, 2 = 1% to 3%, 3 = 4% to 6%, 4 = 7% to 12%, 5 = 13% to 25%, 6 = 26% to 50%, 7 = 51% to 87%, and 8 = 88% to 100% of leaves visually displaying PM. The net photosynthetic (Pn) rates were measured using an infrared gas analyzer. In the first experiment, trees sprayed pre-inoculation with Golden Natur'l, lecithin, lecithin/MD 1, or Latron B-1956 formulation had less PM than control trees at 19 and 24 days after spraying (DAS). Pn of leaves sprayed with lecithin or Latron B-1956 formulations had 68% and 40% lower Pn rates, respectively, of the control leaves at one DAS. However, by 11 DAS, none of the SO formulations significantly affected Pn rates. Leaves of plants (expt. 2) sprayed with teric/termul, lauriciden, lecithin, and lecithin/MD 2 formulations had less PM than control trees at 28 DAS. All formulations reduced Pn rates at 6 DAS, with only Golden Natur'l treated leaves recovering to rates similar to control leaves by 15 DAS.

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T. Casey Barickman, Dean A. Kopsell and Carl E. Sams

One important regulator that coordinates response to environmental stress is the hormone abscisic acid (ABA), which is synthesized from xanthophyll pigments. Despite the fact that there is strong evidence of increases in ABA concentrations under various environmental stresses, information concerning the effects of exogenous ABA applications on leaf pigments and fruit carotenoids in tomato (Solanum lycopersicum) is lacking. This study investigated the impacts of root tissue ABA applications on tomato leaf and fruit pigmentation concentrations of ‘MicroTina’ and ‘MicroGold’ tomato plants. Tomato plants were treated with increasing concentrations of ABA in the nutrient solution. Therefore, the purpose of this study was to determine dose–response effects of ABA treatment in solution culture for maximum leaf pigmentation and fruit carotenoids in two distinct genotypes of dwarf tomato. Because ABA is a product of the carotenoid biosynthetic pathway, we hypothesized that applications of ABA treatments would have a positive impact on leaf chlorophylls and carotenoids. Applications of ABA treatments may also have a positive impact on tomato fruit carotenoids. The results indicated that ‘MicroTina’ plants treated with ABA (0.5, 5.0, and 10.0 mg·L−1) had a significant increase in β-carotene [BC (P ≤ 0.001)], lutein [LUT (P ≤ 0.001)], zeaxanthin [ZEA (P ≤ 0.05)], and neoxanthin [NEO (P ≤ 0.001)] in the leaf tissue. In ‘MicroGold’ tomato plants, carotenoids responded similarly. For example, there were significant increases in BC (P ≤ 0.01), LUT (P ≤ 0.001), ZEA (P ≤ 0.05), and NEO (P ≤ 0.001). In ‘MicroTina’ tomato leaves, there were significant increases in chlorophyll a [Chl a (P ≤ 0.001)] and chlorophyll b [Chl b (P ≤ 0.001)] concentrations. Furthermore, there were significant increases in Chl a (P ≤ 0.001) and Chl b (P ≤ 0.001) in ‘MicroGold’ leaf tissue. In ‘MicroTina’ tomato fruit tissue, the concentration increased significantly for lycopene [LYCO (P ≤ 0.01)]. However, in ‘MicroGold’, there were no significant changes in BC and LUT concentrations. In addition, LYCO was found to be below detection limits in ‘MicroGold’ tomato fruit. Therefore, ABA has been shown to positively change tomato leaf pigments in both genotypes and fruit tissue carotenoid concentrations in ‘MicroTina’ tomato.

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Larry S. Kennedy, William B. Beavers and Carl E. Sams

A common problem of researchers concerned with micronutrient plant nutrition is the development of a reliable and affordable experimental system. If nutrient distribution is uneven or subject to outside contamination, then the time and resources dedicated to a project will have been wasted. We have devised a dependable and cost effective nutrient distribution system which has many practical applications. This design is relatively maintenance free, easily adaptable to existing greenhouse conditions and limits the possibility of outside contamination. Using perlite as the rooting medium, our system is constructed of easily obtainable hardware and mechanical components. The total material cost of our system, which included three nutrient treatments, was approximately $800. This resulted in a conservative estimate of $12.50 per plant in our particular study. However, the cost of a larger experiment would be reduced considerably since additional replications could be added at approximately $2.00 each. The experimental set-up is described along with the initial cost analysis.

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Larry S. Kennedy, Carl E. Sams and Effin T. Graham

Broccoli (Brassica oleraceae L. var. Italica cv. `Premium Crop') plants grown in perlite were supplied with nutrient solutions containing three levels of added boron (0.04 (severely deficient), 0.08 (moderately deficient) or 0.80 (normal) mg L-1). These treatments produced plants exhibiting either obvious (0.04 mg L-1) or no visual boron deficiency symptoms (0.08 and 0.80 mg L-1). At horticultural maturity, cross sections were taken in the upper and mid stem regions. The specimens were mounted on slides after being processed through a biological staining series. Boron availability was found to be correlated with the progressive internal deterioration of the stem which was observed histologically. An examination of staining patterns indicated that possibly a lignification process accompanies and contributes to hollow stem development. We have previously noted an increase in phenolic compounds and fiber content of broccoli produced under boron deficient conditions. The histological evidence of lignification further substantiates that boron deficiency induces changes in cell wall structure which may contribute to the development of hollow stem.