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  • Author or Editor: Carl E. Sams x
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The use of light-emitting diodes (LEDs) for plant production is a new field of research that has great promise to optimize wavelength-specific lighting systems for precise management of plant physiological responses and important secondary metabolite production. In our experiment, hydroponically cultured kale plants (Brassica oleracea L. var. acephala D.C.) were grown under specific LED wavelength treatments of 730, 640, 525, 440, and 400 nm to determine changes in the accumulation of chlorophylls, carotenoids, and glucosinolates. Maximum accumulation, on a fresh mass basis, of chlorophyll a and b and lutein occurred at the wavelength of 640 nm, whereas β-carotene accumulation peaked under the 440-nm treatment. However, when lutein was measured on a dry mass basis, maximum accumulation was shifted to 440 nm. Sinigrin was the only glucosinolate to respond to wavelength treatments. Wavelength control using LED technology can affect the production of secondary metabolites such as carotenoids and glucosinolates with irradiance levels also a factor in kale. Management of irradiance and wavelength may hold promise to maximize nutritional potential of vegetable crops grown in controlled environments.

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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.

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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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Glucosinolates (GS) are important secondary plant metabolites present in several plant species, including Arabidopsis thaliana (L.) Heynh. Although genotypic differences among a limited number of samples from a limited geographical range have been reported, there have been few studies exploring the variation from a wider genetic base. The objective of this study was to explore the genetic variation for GS in A. thaliana collected throughout the world. We screened 58 A. thaliana ecotypes collected from the geographic area of lat. 15° N to lat. 59° N and long. 137° E to long. 123° W. Elevation in these areas ranged from sea level to over 480 m. We believe that this study has covered a large geographical region and captured most of the available genetic variation in A. thaliana for GS. There was no geographical trend in A. thaliana shoot or seed tissue for GS concentration. Total shoot GS ranged from 1.1 to 52.8 μmol·g−1 dry weight (DW), averaging 9.3 μmol·g−1 DW among all ecotypes. Total seed GS ranged from 1.6 to 41.8 μmol·g−1 DW with an average of 16.8 μmol·g−1 DW among all ecotypes. Low and high GS-accumulating A. thaliana ecotypes identified in this study may provide a basis for further genetic analysis for GS metabolism. Information provided may also prove useful for improving concentrations of nutritionally beneficial GS in vegetable Brassicas.

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Plant growth regulators (PGRs) are chemicals used on a wide range of horticultural crops. These exogenous chemicals, similar to endogenous plant hormones, regulate plant development and stimulate a desired growth response, such as control of plant height. One such PGR is abscisic acid (ABA), which has been used effectively to improve fruit quality, specifically sugars and phytonutrients. The purpose of this study was to examine the effects of exogenous applications of ABA on tomato (Solanum lycopersicum) fruit quality, such as carotenoids, soluble sugars and organic acids, and ABA on tomato leaf chlorophylls and carotenoids. Furthermore, this study compared how ABA and calcium (Ca) treatments together affect fruit quality and whether there are added benefits to treating plants with both simultaneously. ABA treatments proved effective in increasing tomato fruit soluble sugars and decreasing organic acid concentrations. This study demonstrated that ABA is a viable PGR to significantly improve tomato fruit quality, specifically pertaining to carotenoids, soluble sugar, and organic acid concentrations.

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Light is one of the most important environmental stimuli impacting plant growth and development. Plants have evolved specialized pigment-protein complexes, commonly referred to as photoreceptors, to capture light energy to drive photosynthetic processes, as well as to respond to changes in light quality and quantity. Blue light can act as a powerful environmental signal regulating phototropisms, suppression of stem elongation, chloroplast movements, stomatal regulation, and cell membrane transport activity. An emerging application of light-emitting diode (LED) technology is for horticultural plant production in controlled environments. Work by our research group is measuring important plant responses to different wavelengths of light from LEDs. We have demonstrated positive impacts of blue wavelengths on primary and secondary metabolism in microgreen and baby leafy green brassica crops. Results show significant increases in shoot tissue pigments, glucosinolates, and essential mineral elements following exposure to higher percentages of blue wavelengths from LED lighting. The perception of energy-rich blue light by specialized plant photoreceptors appears to trigger a cascade of metabolic responses, which is supported by current research showing stimulation of primary and secondary metabolite biosynthesis following exposure to blue wavelengths. Management of the light environment may be a viable means to improve concentrations of nutritionally important primary and secondary metabolites in specialty vegetable crops.

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Light emitting diodes (LEDs) can produce a wide range of narrowband wavelengths with varying intensities. Previous studies have demonstrated that supplemental blue (B) and red (R) wavelengths from LEDs impact plant development, physiology, and morphology. High-pressure sodium (HPS) lighting systems are commonly used in greenhouse production, but LEDs have gained popularity in recent years because of their improved energy efficiency and spectral control. Research is needed to determine the efficacy of supplementary B and R LED narrowband wavelengths compared with traditional lighting systems like HPS in terms of yield, quality, and energy consumption for a variety of greenhouse-grown high-value specialty crops. The objective of this study was to determine the impact of LED and HPS lighting on greenhouse hydroponic basil (Ocimum basilicum var. ‘Genovese’) biomass production and edible tissue nutrient concentrations across different growing seasons. Basil was chosen because of its high demand and value among restaurants and professional chefs. A total of eight treatments were used: one nonsupplemented natural light (NL) control; one HPS treatment; and six LED treatments (peaked at 447 nm/627 nm, ±20 nm) with progressive B/R ratios (10B/90R; 20B/80R; 30B/70R; 40B/60R; 50B/50R; and 60B/40R). Each supplemented light (SL) treatment provided 8.64 mol·m−2·d−1 (100 µmol·m−2·s−1, 24 h·d−1). The daily light integral (DLI) of the NL control averaged 9.5 mol·m−2·d−1 across all growing seasons (ranging from 4 to 18 mol·m−2·d−1). Relative humidity averaged 50%, with day/night temperatures averaging 27.4 °C/21.8 °C, respectively. LED treatments had the greatest total fresh biomass (FM) and dry biomass (DM) accumulation; biomass for LED treatments were 1.3 times greater on average than HPS, and 2 times greater than the NL control. Biomass partitioning revealed that the LED treatments had more FM and DM for the individual main stem, shoots, and leaves of each plant at varying levels. LED treatments resulted in greater height and main stem diameter. Some essential nutrient concentrations were impacted by SL treatments and growing season. An energy analysis revealed that on average, narrowband B/R LED treatments were 3 times more energy efficient at increasing biomass over HPS. LED treatments reduced SL energy cost per gram FM increase by 95% to 98% when compared with HPS. In addition, the rate of electricity consumption to biomass increase varied across LED treatments, which demonstrates that basil uses different B/R narrowband ratios at varying efficiencies. This experiment shows that spectral quality of both supplemental sources and natural sunlight impacts primary metabolic resource partitioning of basil. The application of LED lighting systems to supplement natural DLI and spectra during unfavorable growing seasons has the potential to increase overall biomass accumulation and nutrient concentrations in a variety of high-value specialty crops.

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Soybean [Glycine max (L.) Merrill] oil was applied to apple trees [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] as a summer spray in six studies to determine if it controls European red mites [Panonychus ulmi (Koch.)], how it affects net CO2 assimilation (A), and if it causes phytotoxicity. Sprays of 0.5%, 1.0%, and 1.5% soybean oil {TNsoy1 formulation [soybean oil premixed with Latron B-1956 (LAT) spreader-sticker at 10 oil: 1 LAT (v/v)]} reduced mite populations by 94%. Sprays of 1% and 2% soybean oil reduced mite populations to three and four mites per leaf, respectively, compared to 25 per leaf on water-sprayed plants. Soybean oil concentrations of 1.0% and 1.5% applied to whole trees reduced A for less than 7 days. Phytotoxicity did not occur when soybean oil was applied with an airblast sprayer at concentrations of 1.0% and 1.5% or with a mist bottle at 2%. Phytotoxicity occurred when soybean oil was applied with a mist bottle at 4% and 6%, which left soybean oil leaf residues of 0.22 to 0.50 mg·cm-2. No phytotoxicity occurred with 4% SunSpray, which resulted in a mean leaf residue of only 0.13 mg·cm-2. Spraying 1% soybean oil tended to give better mite control than 1% SunSpray Ultra-Fine oil, but caused greater oil residues and a greater reduction in A.

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Applications of soybean oil to dormant peach [Prunus persica (L.) Batsch] trees were tested for prebloom thinning of flower buds in five separate experiments. Data were combined from experiments in which 2.5% to 20% emulsified soybean oil was sprayed on `Belle of Georgia' or `Redhaven' trees. The number of dead flower buds was concentration-dependent with maximum bud kill of 53% occurring with application of 12% soybean oil. The amount of thinning was fairly consistent from year to year, ranging from 34% to 51% when 10% soybean oil was applied, but was less consistent when 5% was applied, ranging from 6% to 40%. Overthinning by midwinter applications of soybean oil occurred in one experiment when bud mortality on nontreated trees was 40% due to natural causes. Mild to moderate spring freezes occurred in three experiments, but did not reduce yield more in soybean oil–thinned than in nontreated trees. Flower bud survival was improved when trees were sprayed with 10% or 12% soybean oil prior to a –4 °C spring frost. Applications of soybean oil to dormant trees thinned flower buds, reduced the amount of hand thinning required, and hastened fruit maturity.

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Selenium (Se) is an essential mammalian micronutrient. Adult humans have a daily requirement of 55 to 70 μg/day Se depending on sex and pregnancy/lactation for females. In addition, recent studies have shown health benefits with dietary Se supplementation of 100 to 200 μg/day Se. However, daily intakes in humans greater than 900 μg Se will result in toxicity called selenosis. Although not essential in plant nutrition, some species can bioaccumulate Se. Brassica and Allium species became prime candidates for Se enrichment because of their ability to accumulate and tolerate high concentrations of Se in edible tissues; however, there is now concern that these species are too efficient at selenization and overconsumption of their selenized tissues could result in selenosis. Herbal crop species are consumed regularly in the diet for their culinary flavor attributes. Basil (Ocimum basilicum L.) and cilantro (Coridandrum sativum L.) are not classified as Se accumulators. Therefore, a study was undertaken to determine the potential to selenize basil and cilantro through foliar Se applications to consistently supplement diets with nutritionally beneficial levels of Se. Plants of each species were grown in both growth chamber and field environments and treated with foliar applications (5 mL per plant) of selenate-Se and selenite-Se at concentrations of 0, 2, 4, 8, 16, and 32 mg·L−1 Se. Crops received three separate foliar applications at ≈5-day intervals beginning 24 to 28 days after planting for the growth chamber plants and 50 days after planning for the field environment. Selenium accumulation in both basil and cilantro leaf tissues increased linearly under both selenate-Se (P ≤ 0.001) and selenite-Se (P ≤ 0.001) foliar treatments in growth chamber and field evaluations. Maximum Se leaf tissue concentrations for basil and cilantro ranged from 13 to 55 μg·g−1 Se dry weight. Selenization of basil and cilantro is possible through foliar Se applications, and Se fortification of herbal crops may provide alternative delivery systems in human diets.

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