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Horticulturae, Volume 4, Issue 2 (June 2018) – 5 articles

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11 pages, 1386 KiB

Open AccessFeature PaperArticle

Effects of Elevated Temperature and Potassium on Biomass and Quality of Dark Red ‘Lollo Rosso’ Lettuce

by William L. Sublett, T. Casey Barickman and Carl E. Sams

Horticulturae 2018, 4(2), 11; https://doi.org/10.3390/horticulturae4020011 - 16 Jun 2018

Cited by 25 | Viewed by 7054

Abstract

Lettuce is an economically important crop for small and medium-sized growers. When grown in adverse environmental conditions, lettuce is vulnerable to a deterioration of yield and quality. Research concerning the impact of elevated potassium (K) levels on leafy vegetables, such as lettuce, is lacking. Therefore, seeds of dark-red ‘Lollo’ lettuce were germinated under greenhouse conditions at 25/20 °C (day/night). Plants were transferred into 11-L containers and placed into growth chambers at 25 and 33 °C. Plants were grown with K treatments of 117.3 (control), 234.6 (2×), 469.2 (4×), and 4) 938.4 (8×) mg·L⁻¹. Increasing K treatments resulted in a negative quadratic response on lettuce dry mass and generated 14% more leaf calcium at 234.6 mg·L⁻¹. An increase in temperature from 25 to 33 °C increased leaf dry matter and biomass by 40% and 43%, respectively. Leaf water content increased by 3% as temperature increased. Plants grown at 33 °C had greater quercetin glycosides compared to plants grown at 25 °C. The results from this study suggest that temperature is a stronger regulatory factor than increasing K in the determination of lettuce yield and quality. Increasing K concentration to 234.6 mg·L⁻¹ results in greater concentrations of leaf minerals without compromising plant yield. Full article

(This article belongs to the Special Issue Plant Production in Controlled Environment)

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11 pages, 222 KiB

Open AccessArticle

New Media Components and Fertilization to Accelerate the Growth of Citrus Rootstocks Grown in a Greenhouse

by Sandra C. Arce and Dania Rivera

Horticulturae 2018, 4(2), 10; https://doi.org/10.3390/horticulturae4020010 - 10 Jun 2018

Cited by 8 | Viewed by 3959

Abstract

In Puerto Rico, oranges made up $6,452,000 of the agricultural gross income for 2014–2015. Today, citrus greening (CG) is the most aggressive disease affecting the citrus industry in the whole world. This disease causes dieback of the plant, among other symptoms, which is resulting in the reduction of citrus trees in the field across the world. Currently, it is recommended to grow citrus rootstocks in nurseries to produce disease-free trees. The objective of this investigation was to evaluate (before and after grafting) the effect of different substrate mixes and quantities of fertilizers on the rootstocks Carrizo citrange and Swingle citrumelo in order to accelerate their development inside of a protected structure. The treatments were: Promix + sand (control) (1:1), Promix + sand + coco peat (1:1:1), Promix + sand + coffee compost (1:1:1) and Promix + sand + rice husk (1:1:1). Two 18-6-2 fertilizer treatments were also evaluated: 5.6 g and 8.5 g. The substrate that contained 33% rice husks negatively influenced every parameter evaluated for both rootstocks. Carrizo presented better development on the coffee compost mix, while Swingle did not exhibit significant differences among any substrates, except on rice husk, for most of the parameters. “Rhode Red Valencia” presented better results for dry weight when grafted on Carrizo with the coffee substrate. The rice husk substrate is not recommended for the citrus tree production at the nursery level. Full article

(This article belongs to the Special Issue Plant Production in Controlled Environment)

10 pages, 999 KiB

Open AccessArticle

Coconut Leaf Age and Coconut Rhinoceros Beetle Herbivory Influence Leaflet Nutrients, Metals, and Lignin

by Thomas E. Marler

Horticulturae 2018, 4(2), 9; https://doi.org/10.3390/horticulturae4020009 - 8 Jun 2018

Cited by 2 | Viewed by 6358

Abstract

The coconut rhinoceros beetle (CRB, Oryctes rhinoceros L.) is a serious pest of coconut (Cocos nucifera L.) in many tropical regions, however the influences of CRB herbivory on the coconut leaf chemistry are unknown. This limits our ability to predict the afterlife decomposition dynamics of the damaged coconut leaf litter. Mature green and senesced leaflet tissues were collected from coconut trees on the island of Guam, where coconut is native and CRB is invasive. Mineral, metal, and lignin concentrations were quantified to determine the nutrient limitations and the litter quality traits. Nitrogen was increased and the elements that are not resorbed during leaf senescence were decreased by the CRB damage. The important litter stoichiometric traits carbon/nitrogen and lignin/nitrogen were decreased by the CRB damage. The results indicate that CRB herbivory may limit green leaf nutrition in Guam’s soils and increase the senesced leaf litter decomposition speed and nutrient turnover rates. Full article

(This article belongs to the Special Issue Food Safety Pertinent to Fresh Produce)

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10 pages, 626 KiB

Open AccessFeature PaperArticle

Growth and Physiological Responses of Lettuce Grown under Pre-Dawn or End-Of-Day Sole-Source Light-Quality Treatments

by Skarleth Chinchilla, Luigi G. Izzo, Edzard Van Santen and Celina Gómez

Horticulturae 2018, 4(2), 8; https://doi.org/10.3390/horticulturae4020008 - 7 Jun 2018

Cited by 17 | Viewed by 5262

Abstract

The objective of this study was to evaluate growth and physiological responses of ‘Cherokee’ and ‘Waldmann’s Green’ lettuce (Lactuca sativa) exposed to small changes in light quality and intensity within a 24-h period. Three pre-dawn (PD; 0600 to 0700) and three end-of-day (EOD; 2100 to 2200) treatments were evaluated in the study, each providing 50 ± 2 µmol·m⁻²·s⁻¹ of either blue, red, or broadband white light from light-emitting diodes (LEDs). To account for the main daily light integral (DLI), broadband white LEDs provided 210 ± 2 µmol·m⁻²·s⁻¹ from 0700 to 2200 or from 0600 to 2100 for the PD or EOD treatments, respectively. A control treatment was included which provided 200 ± 2 µmol·m⁻²·s⁻¹ of white light from 0600 to 2200. All treatments provided a DLI of 11.5 mol·m⁻²·day⁻¹ over a 16-h photoperiod. Regardless of cultivar, no treatment difference was measured for hypocotyl length or leaf number. However, plants grown under EOD-blue or PD-white had up to 26% larger leaves than those grown under PD-red and 20% larger leaves than control. In addition, plants grown under EOD-blue produced up to 18% more shoot fresh mass compared to those grown under control, EOD-red, or PD-red. Contrasts for gas-exchange data collected during the main photoperiod showed that light quality was not significant within PD or EOD for any of the parameters evaluated. However, regardless of light quality, stomatal conductance (g_s) and transpiration (E) were up to 34% and 42% higher, respectively, for EOD-grown plants compared to control. Our results suggest that 1 h of low intensity EOD-blue light has the potential to promote lettuce growth by increasing leaf area and shoot fresh mass when the main DLI from sole-source lighting is provided by broadband white LEDs. Full article

(This article belongs to the Special Issue Plant Production in Controlled Environment)

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13 pages, 1712 KiB

Open AccessArticle

Do Extended Cultivation Periods and Reduced Nitrogen Supply Increase Root Yield and Anthocyanin Content of Purple Carrots?

by Lilian Schmidt, Sophia Sorg, Susanne Tittmann, Johannes F. J. Max and Jana Zinkernagel

Horticulturae 2018, 4(2), 7; https://doi.org/10.3390/horticulturae4020007 - 16 Apr 2018

Cited by 2 | Viewed by 4543

Abstract

Purple carrots are rich in anthocyanins which are interesting as natural dyes in food and beverages. It is, thus, relevant to increase the concentration of anthocyanins by agricultural practices. We tested whether the combination of reduced nitrogen (N) supply and extended harvesting periods maximized the anthocyanin concentration of purple carrot roots, ideally without reducing their yield. The carrot variety ‘Deep Purple’ was grown with total N supplies of 220 kg N ha⁻¹ (controls) and 73 kg N ha⁻¹ (reduced N), respectively. Upon harvests in September, October and November, root yield and quality were assessed. Concentrations of chlorophylls (leaves) and anthocyanins (roots and leaves) were determined by spectroscopic and chemical analyses, and carbon and N content were quantified. Reduced N supply neither affected leaf or root biomass nor their chemical composition. Later harvests did not impact the yield of roots, but increased their diameter by 8.5–20%. Additionally, the anthocyanin concentrations of the roots increased by 40–50% in the controls, but not in N-limited plants, at late harvests. Consequently, extending the harvesting period might increase the anthocyanin concentration in roots of ‘Deep Purple’. Moreover, N supply might be reduced for this carrot variety without negative effects on root yield. Full article

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