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Horticulturae, Volume 5, Issue 1 (March 2019)

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Cover Story (view full-size image) The quality index of citrus (Brix/acid ratio) was assessed with fluorescence spectroscopy using [...] Read more.
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Open AccessArticle
Vermiliquer (Vermicompost Leachate) as a Complete Liquid Fertilizer for Hydroponically-Grown Pak Choi (Brassica chinensis L.) in the Tropics
Horticulturae 2019, 5(1), 26; https://doi.org/10.3390/horticulturae5010026
Received: 5 November 2018 / Revised: 25 February 2019 / Accepted: 6 March 2019 / Published: 15 March 2019
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Abstract
The processing of organic wastes and composts by worms results in castes and vermiliquer (i.e., vermicompost leachate). Both castes and vermiliquer contain plant available nutrients, the latter better suited to hydroponic operations, but the optimum pH for worm productivity and vermiliquer production makes [...] Read more.
The processing of organic wastes and composts by worms results in castes and vermiliquer (i.e., vermicompost leachate). Both castes and vermiliquer contain plant available nutrients, the latter better suited to hydroponic operations, but the optimum pH for worm productivity and vermiliquer production makes the latter too alkaline for hydroponics. We show that under optimal hydroponic management practices, the growth and yield of pak choi (Brassica chinensis) based entirely on pH buffered vermiliquer collected after 8–10 weeks of vermicomposting was comparable with those treated with a conventional inorganic hydroponic fertiliser. Nitric acid proved to be a superior pH buffer compared with orthophosphoric acid. The total fresh weight in the nitric acid buffered vermiliquer treatments ranged from 70% to 98% of the total fresh weight of the control. However, the non-buffered hydroponic production of pak choi using off-line (batch) vermiliquer or direct linkage with vermifarms was not successful. There were no statistically significant differences between pak choi yields using vermiliquer from kitchen wastes or composted paunch materials. A 50% dilution of vermiliquer led to yield loss, but less proportionately than the dilution, and the use of pot hydroponics rather than nutrient film technique (NFT) hydroponics led to a better performance of pak choi under less favourable conditions. This is the first report of comparable yields between vermiliquer treatments and an inorganic nutrient source and highlights the feasibility and commercial potential of this hydroponic practice. Full article
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Open AccessReview
Risk of Human Pathogen Internalization in Leafy Vegetables During Lab-Scale Hydroponic Cultivation
Horticulturae 2019, 5(1), 25; https://doi.org/10.3390/horticulturae5010025
Received: 13 February 2019 / Revised: 3 March 2019 / Accepted: 7 March 2019 / Published: 15 March 2019
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Abstract
Controlled environment agriculture (CEA) is a growing industry for the production of leafy vegetables and fresh produce in general. Moreover, CEA is a potentially desirable alternative production system, as well as a risk management solution for the food safety challenges within the fresh [...] Read more.
Controlled environment agriculture (CEA) is a growing industry for the production of leafy vegetables and fresh produce in general. Moreover, CEA is a potentially desirable alternative production system, as well as a risk management solution for the food safety challenges within the fresh produce industry. Here, we will focus on hydroponic leafy vegetable production (including lettuce, spinach, microgreens, and herbs), which can be categorized into six types: (1) nutrient film technique (NFT), (2) deep water raft culture (DWC), (3) flood and drain, (4) continuous drip systems, (5) the wick method, and (6) aeroponics. The first five are the most commonly used in the production of leafy vegetables. Each of these systems may confer different risks and advantages in the production of leafy vegetables. This review aims to (i) address the differences in current hydroponic system designs with respect to human pathogen internalization risk, and (ii) identify the preventive control points for reducing risks related to pathogen contamination in leafy greens and related fresh produce products. Full article
(This article belongs to the Special Issue Food Safety Pertinent to Fresh Produce)
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Open AccessArticle
In Vitro Establishment of ‘Delite’ Rabbiteye Blueberry Microshoots
Horticulturae 2019, 5(1), 24; https://doi.org/10.3390/horticulturae5010024
Received: 18 January 2019 / Revised: 20 February 2019 / Accepted: 25 February 2019 / Published: 8 March 2019
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Abstract
Micropropagation is an important technique for clonal mass propagation and a tool for in vitro studies. One of the first steps to overcome in this process is the establishment of new explants in vitro. ‘Delite’ rabbiteye blueberry was cultured in vitro with four [...] Read more.
Micropropagation is an important technique for clonal mass propagation and a tool for in vitro studies. One of the first steps to overcome in this process is the establishment of new explants in vitro. ‘Delite’ rabbiteye blueberry was cultured in vitro with four cytokinins (zeatin (ZEA), 6-(γ-γ-dimethylallylamino)-purine (2iP), 6-benzylaminopurine (BAP), and kinetin (KIN)) at eight concentrations (0, 2.5, 5, 10, 20, 30, 40, and 50 µM). Additionally, nine combinations of nitrogen salts were tested, using Woody Plant Medium (WPM) and a modified WPM as the basic medium. ZEA and 2iP showed better responses, but ZEA was superior at lower (2.5 µM) concentrations (89.7% survival, 81.3% shoot formation, 1.3 shoots, 13.8 mm shoot length, 10.0 leaves). BAP and KIN showed very low responses. In the combinations of salts with modified WPM, no differences were observed. However, the original WPM with treatments of 0.5 × NH4NO3 and 1 × Ca(NO3)2, 0.5 × NH4NO3 and 0.5 × Ca(NO3)2, and the modified WPM alone showed the lowest rates of survival and shoot formation and the shortest shoot lengths. The highest shoot lengths were observed in treatments with the original WPM, 1.5 × NH4NO3 and 0.5 × Ca(NO3)2, and 1.5 × NH4NO3 and 1.5 × Ca(NO3)2. This initial study with ‘Delite’ can be the basis for further experiments with different combinations of salts, 2iP, and ZEA. Full article
(This article belongs to the Special Issue Innovation in Propagation of Fruit, Vegetable and Ornamental Plants)
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Open AccessArticle
Postharvest Dips of Persimmon Fruit in Gibberellic Acid: An Efficient Treatment to Improve Storability and Reduce Alternaria Black Spot
Horticulturae 2019, 5(1), 23; https://doi.org/10.3390/horticulturae5010023
Received: 13 January 2019 / Revised: 3 February 2019 / Accepted: 22 February 2019 / Published: 6 March 2019
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Abstract
In Israel, fruit softening during storage and the occurrence of Alternaria black spot (ABS) disease, caused by Alternaria alternata, are the main postharvest factors that reduce quality and impair storability of persimmon fruit. The pathogen causing ABS infects the fruit in the [...] Read more.
In Israel, fruit softening during storage and the occurrence of Alternaria black spot (ABS) disease, caused by Alternaria alternata, are the main postharvest factors that reduce quality and impair storability of persimmon fruit. The pathogen causing ABS infects the fruit in the orchard and remains quiescent until harvest, or renews its development just before harvest but mainly during storage. A preharvest spray with 50 µg·L−1 gibberellin (GA3) significantly improved fruit storability, as determined by fruit firmness and levels of ABS. While GA3 treatments have been commercially applied for more than 30 years, significant limitations of the use of the preharvest treatment like enhancing the risk of a reduced yield have been described. Recent findings suggested that postharvest dip treatments with increased concentrations of GA3 also delayed fruit softening and reduced ABS to similar levels to the commercially applied preharvest treatment in persimmon fruit stored for 3 months at 0 °C. Postharvest GA3 dip treatments at concentrations ranging from 500 to 1500 µg·L−1 were similarly more efficient in the prevention of fruit softening and ABS development than the 50 µg·L−1 preharvest spray. Present results indicated that postharvest GA3 treatment physiologically affects fruit firmness and susceptibility to ABS during storage. Full article
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Open AccessArticle
Citrulline and Arginine Content of Taxa of Cucurbitaceae
Horticulturae 2019, 5(1), 22; https://doi.org/10.3390/horticulturae5010022
Received: 13 December 2018 / Revised: 19 February 2019 / Accepted: 28 February 2019 / Published: 4 March 2019
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Abstract
Watermelon is the most significant, natural plant source of L-citrulline, a non-proteinaceous amino acid that benefits cardiovascular health and increases vasodilation in many tissues of the body. Watermelon is a member of the Cucurbitaceae, which includes squash, melon, pumpkin, and cucumber. It is [...] Read more.
Watermelon is the most significant, natural plant source of L-citrulline, a non-proteinaceous amino acid that benefits cardiovascular health and increases vasodilation in many tissues of the body. Watermelon is a member of the Cucurbitaceae, which includes squash, melon, pumpkin, and cucumber. It is possible that other cucurbits could be good sources of citrulline or of arginine, its direct precursor. Twenty-one cultigens were evaluated in triplicate at two locations in North Carolina to estimate citrulline and arginine amounts and variation due to cultigen, replication, and environment. Cultigens containing the highest amount of citrulline (based on LS means) in g/kg fresh weight were ’Crimson Sweet’ watermelon (2.85), ’Dixielee’ watermelon (2.43), casaba-type melon (0.86), mouse melon (0.64), and horned melon rind (0.45). Additionally, mouse melon, horned melon, and bitter gourd (arils) may be interesting sources of arginine-family amino acids, perhaps because of their large seed and aril content relative to mesocarp. Full article
Open AccessArticle
Use of Diatomaceous Earth as a Silica Supplement on Potted Ornamentals
Horticulturae 2019, 5(1), 21; https://doi.org/10.3390/horticulturae5010021
Received: 28 January 2019 / Revised: 15 February 2019 / Accepted: 22 February 2019 / Published: 1 March 2019
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Abstract
The role of silica as a needed supplement in soilless media is gaining interest. This research studied the effects of diatomaceous earth as a supplement on growth and flower characteristics, physiology, and nutrient uptake in dahlia (Dahlia Cav. × hybrida ‘Dahlinova Montana’), [...] Read more.
The role of silica as a needed supplement in soilless media is gaining interest. This research studied the effects of diatomaceous earth as a supplement on growth and flower characteristics, physiology, and nutrient uptake in dahlia (Dahlia Cav. × hybrida ‘Dahlinova Montana’), black-eyed Susan (Rudbeckia hirta L. ‘Denver Daisy’), and daisy (Gerbera jamesonii L. ‘Festival Light Eye White Shades’). Plants were either well-watered at 10 centibars or water-stressed at 20 centibars. Silicon treatments included top-dressed at 20, 40, 60, and 80 g, or incorporated at 50, 100, 150, and 200 g, in Metro-Mix 360 media without silica plus a control and one treatment of new Metro-Mix 360 with silica already incorporated. Significant effects were seen from diatomaceous earth supplementation, irrigation, and interaction in all plants; growth and flower characteristics, leaf nutrient content, and tolerance to stress were improved by application of diatomaceous earth. An increase in leaf N, P, K, Mg, and Ca was observed for dahlia ‘Dahlinova Montana’ and black-eyed Susan ‘Denver Daisy’. Transpiration was maintained in all three species due to silica supplementation under water-stress. Metro-Mix with silica was similar to the Metro-mix without silica and equivalent to most treatments with supplemental silica for all three species. Full article
Open AccessArticle
Effects of Seeding Pattern and Cultivar on Productivity of Baby Spinach (Spinacia oleracea) Grown Hydroponically in Deep-Water Culture
Horticulturae 2019, 5(1), 20; https://doi.org/10.3390/horticulturae5010020
Received: 1 December 2018 / Revised: 8 February 2019 / Accepted: 21 February 2019 / Published: 28 February 2019
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Abstract
Baby spinach (Spinacia oleracea) was grown in a bench-scale deep-water culture (DWC) system in expanded polystyrene (EPS) plug trays. Two experiments were performed. In the first, different seeding patterns, [1-2-1-2…] or [3-0-3-0…] seeds per sequential cell, at the same overall density [...] Read more.
Baby spinach (Spinacia oleracea) was grown in a bench-scale deep-water culture (DWC) system in expanded polystyrene (EPS) plug trays. Two experiments were performed. In the first, different seeding patterns, [1-2-1-2…] or [3-0-3-0…] seeds per sequential cell, at the same overall density per tray, were compared to evaluate the potential of an EPS tray designed with fewer cells, but sown with more seeds per cell (to preserve canopy density). Using such a flat would lower growing substrate requirements. Seeding in the [3-0-3-0…] pattern reduced seed germination, but only by 5%. Harvested fresh weight was also less numerically in the [3-0-3-0…] pattern but not statistically. The second experiment observed cultivars Carmel, Seaside and Space grown concurrently. Carmel had the highest germination, nearly 100%, which was significantly greater than Seaside but not Space. Germination for Space was not significantly different from that of Seaside. Carmel also had the highest harvested fresh weight but was not significantly different from Space; both Carmel and Space produced significantly more harvested fresh weight than Seaside. Full article
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Open AccessArticle
Yield and Fruit Properties of Husk Tomato (Physalis phyladelphica) Cultivars Grown in the Open Field in the South of West Siberia
Horticulturae 2019, 5(1), 19; https://doi.org/10.3390/horticulturae5010019
Received: 23 December 2018 / Revised: 12 January 2019 / Accepted: 7 February 2019 / Published: 18 February 2019
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Abstract
Husk tomato (Physalis philadelphica Lam.) a source of functional food and medicinal compounds, has attracted renewed interest for production in temperate zones. Field-grown husk tomato yield and fruit properties and their relationship with soil chemistry and temperature were studied in the south [...] Read more.
Husk tomato (Physalis philadelphica Lam.) a source of functional food and medicinal compounds, has attracted renewed interest for production in temperate zones. Field-grown husk tomato yield and fruit properties and their relationship with soil chemistry and temperature were studied in the south of West Siberia, Russia, at five experimental sites. At each site, a microplot experiment with two cultivars was conducted. Basic soil chemical properties and fruit pH and dry matter, total carbon, nitrogen, and ascorbic acid content were determined. Both cultivars grew and yielded very well, producing on average 70 fruits, or 1.46 kg, per plant, with 14 mg ascorbic acid per 100 g fresh weight, 9.0% dry matter, and juice pH of 4.1. Variation in environmental conditions among sites was the major factor determining production and fruit property variation, with cultivar biology accounting for 10%. The cultivars responded differently to some soil properties, but generally their yield and fruit quality depended on soil pH and labile phosphorous and potassium. Thus, husk tomato has remarkable capacity for vigorous yields in unprotected conditions in West Siberia, despite air and soil temperatures that are much lower than in its region of origin. Detailed studies are needed to elucidate its response to varying solar radiation and atmospheric precipitation. Full article
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Open AccessArticle
Improved Tolerance for Onion Thrips and Iris Yellow Spot in Onion Plant Introductions after Two Selection Cycles
Horticulturae 2019, 5(1), 18; https://doi.org/10.3390/horticulturae5010018
Received: 22 December 2018 / Revised: 6 February 2019 / Accepted: 15 February 2019 / Published: 16 February 2019
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Abstract
Iris yellow spot (IYS), a disease caused by Iris yellow spot virus (IYSV) and spread by onion thrips, is a devastating disease of onion bulb and seed production. The development of onion germplasm resistant to IYS and/or thrips is crucial to onion production, [...] Read more.
Iris yellow spot (IYS), a disease caused by Iris yellow spot virus (IYSV) and spread by onion thrips, is a devastating disease of onion bulb and seed production. The development of onion germplasm resistant to IYS and/or thrips is crucial to onion production, since host plant resistance is unknown for both pests. During the summer of 2010 and 2012, plants with fewer IYS disease symptoms were selected from a screening of plant introduction accessions (PIs) and first-generation selections, respectively. The resulting progeny from these selected plants were evaluated during the summers of 2013 and 2014 for thrips numbers and IYS symptom expression, and compared with their respective original PIs and a susceptible check, ‘Rumba’. The field experiment was designed such that every plant in the field screening had an equal chance of being infected with IYSV. This study shows that variation for thrips and IYS existed among PIs and first- and second-generation selections. Even though not enough progress towards minimizing IYS severity was evident from this study, we did identify several lines with improved tolerance to onion thrips in first- and second-generation selections. The majority of the selected lines exhibited lower thrips and IYS severity compared to ‘Rumba’, which suggests that the progress towards developing insect- and ultimately disease-resistant germplasm can be achieved. Full article
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Open AccessFeature PaperArticle
Effects of Co-Inoculation of Indole-3-Acetic Acid-Producing and -Degrading Bacterial Endophytes on Plant Growth
Horticulturae 2019, 5(1), 17; https://doi.org/10.3390/horticulturae5010017
Received: 25 December 2018 / Revised: 23 January 2019 / Accepted: 24 January 2019 / Published: 6 February 2019
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Abstract
Bacterial production of indole-3-acetic acid (IAA) and its effects on plant growth have been frequently studied but there have been few studies on the ecology of IAA-degrading bacteria. In this study, among eight endophytic bacterial strains previously isolated from the same sweet potato [...] Read more.
Bacterial production of indole-3-acetic acid (IAA) and its effects on plant growth have been frequently studied but there have been few studies on the ecology of IAA-degrading bacteria. In this study, among eight endophytic bacterial strains previously isolated from the same sweet potato sample including two IAA producers, Klebsiella sp. Sal 1 and Enterobacter sp. Sal 3, all of the strains showed IAA-degrading ability to some extent. Herbaspirillum sp. Sal 6 had the highest activity for IAA and tryptophan. When the IAA producers and the degrader were co-cultured in tryptophan-amended N+MR liquid medium, the concentrations of IAA decreased. Inoculation with Klebsiella sp. Sal 1, the highest IAA producer among the test strains, increased fresh root weight of tomato and radish, but the effect decreased by co-inoculation with IAA-degrading Herbaspirillum sp. Sal 6. Since both strains colonized plant parts at high populations, it was likely that the IAA degrader decreased IAA levels in the plants by degrading IAA and/or its precursor tryptophan. When IAA-producing biofertilizers are used, interactions with IAA degraders in plants should be considered. Full article
(This article belongs to the Special Issue Horticultural Crop Microbiomes)
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Open AccessArticle
Assessing Quantitative Criteria for Characterization of Quality Categories for Grafted Watermelon Seedlings
Horticulturae 2019, 5(1), 16; https://doi.org/10.3390/horticulturae5010016
Received: 26 December 2018 / Revised: 23 January 2019 / Accepted: 28 January 2019 / Published: 2 February 2019
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Abstract
Vegetable grafting is a practice employed worldwide since it helps prevent biotic and abiotic disorders, and watermelon is one of the most important species grafted. The objective of this study was to set critical limits for the characterization of quality categories for grafted [...] Read more.
Vegetable grafting is a practice employed worldwide since it helps prevent biotic and abiotic disorders, and watermelon is one of the most important species grafted. The objective of this study was to set critical limits for the characterization of quality categories for grafted watermelon seedlings. Specifically, watermelon (scion) seedlings were grafted onto squash (rootstock) seedlings, moved into a healing chamber for 7 days, and then transferred into a greenhouse for seven more days. At 7 and 14 days after grafting, experienced personnel assessed grafted seedling quality by categorizing them. The categories derived were Optimum and Acceptable for both time intervals, plus Not acceptable at 14 days after grafting. Optimum seedlings showed greater leaf area, and shoot and root fresh and dry weights at both time intervals. Moreover, they had greater stem diameter, root-to-shoot ratio, shoot dry weight-to-length ratio and Dickson’s quality index compared to the other category at 14 days after grafting. Therefore, Optimum seedlings would likely develop into marketable plants of high quality, with better establishment in the field. Not acceptable seedlings showed considerably inferior development, while Acceptable seedlings were between the other categories, but were still marketable. Full article
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Open AccessArticle
Timing of a Short-Term Reduction in Temperature and Irradiance Affects Growth and Flowering of Four Annual Bedding Plants
Horticulturae 2019, 5(1), 15; https://doi.org/10.3390/horticulturae5010015
Received: 7 December 2018 / Accepted: 23 January 2019 / Published: 1 February 2019
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Abstract
Heating and supplemental lighting are often provided during spring greenhouse production of bedding plants, but energy inputs are a major production cost. Different energy-savings strategies can be utilized, but effects on plant growth and flowering must be considered. We evaluated the impact and [...] Read more.
Heating and supplemental lighting are often provided during spring greenhouse production of bedding plants, but energy inputs are a major production cost. Different energy-savings strategies can be utilized, but effects on plant growth and flowering must be considered. We evaluated the impact and timing of a two-week low-energy (reduced temperature and irradiance) interval on flowering and growth of impatiens (Impatiens walleriana Hook.f. ‘Accent Orange’), pansy (Viola × wittrockiana Gams. ‘Delta Premium Blue Blotch’), petunia (Petunia × hybrida Hort. Vilm.-Andr. ‘Dreams Pink’), and snapdragon (Antirrhinum majus L. ‘Montego Violet’). Flowering was delayed 7 to 10 days when the low-energy exposure occurred before flowering. Flower number was reduced 40–61% in impatiens, 33–35% in petunia (low-energy weeks 5–6 and weeks 7–8, respectively), and 35% in pansy (weeks 5–6). Petunia and impatiens dry mass gradually decreased as the low-energy exposure occurred later in production; petunias were 26% (weeks 5–6) and 33% (weeks 7–8) smaller, and impatiens were 20% to 31% smaller than ambient plants. Estimated energy savings were 14% to 16% for the eight-week period, but only up to 7% from transplant to flowering. Growers can consider including a two-week reduction in temperature and irradiance to reduce energy, provided an additional week of production is scheduled. Full article
(This article belongs to the Special Issue Abiotic Stress Effects on Performance of Horticultural Crops)
Open AccessReview
Effects of Biochar on Container Substrate Properties and Growth of Plants—A Review
Horticulturae 2019, 5(1), 14; https://doi.org/10.3390/horticulturae5010014
Received: 15 November 2018 / Revised: 10 January 2019 / Accepted: 24 January 2019 / Published: 1 February 2019
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Abstract
Biochar refers to a processed, carbon-rich material made from biomass. This article provides a brief summary on the effects of biochar on container substrate properties and plant growth. Biochar could be produced through pyrolysis, gasification, and hydrothermal carbonization of various feedstocks. Biochar produced [...] Read more.
Biochar refers to a processed, carbon-rich material made from biomass. This article provides a brief summary on the effects of biochar on container substrate properties and plant growth. Biochar could be produced through pyrolysis, gasification, and hydrothermal carbonization of various feedstocks. Biochar produced through different production conditions and feedstocks affect its properties and how it performs when incorporated in container substrates. Biochar incorporation affects the physical and chemical properties of container substrates, including bulk density, total porosity, container capacity, nutrient availability, pH, electrical conductivity and cation exchange capacity. Biochar could also affect microbial activities. The effects of biochar incorporation on plant growth in container substrates depend on biochar properties, plant type, percentage of biochar applied and other container substrates components mixed with biochar. A review of the literature on the impact of biochar on container-grown plants without other factors (such as irrigation or fertilization rates) indicated that 77.3% of the studies found that certain percentages of biochar addition in container substrates promoted plant growth, and 50% of the studies revealed that plant growth decreased due to certain percentages of biochar incorporation. Most of the plants tested in these studies were herbaceous plants. More plant species should be tested for a broader assessment of the use of biochar. Toxic substances (heavy metals, polycyclic aromatic hydrocarbons and dioxin) in biochars used in container substrates has rarely been studied. Caution is needed when selecting feedstocks and setting up biochar production conditions, which might cause toxic contaminants in the biochar products that could have negative effects on plant growth. Full article
Open AccessArticle
Evaluation of Two Wild Populations of Hedge Mustard (Sisymbrium officinale (L.) Scop.) as a Potential Leafy Vegetable
Horticulturae 2019, 5(1), 13; https://doi.org/10.3390/horticulturae5010013
Received: 5 October 2018 / Revised: 8 January 2019 / Accepted: 11 January 2019 / Published: 1 February 2019
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Abstract
The minimally processed industry is always looking for produce innovation that can satisfy consumer needs. Wild leafy vegetables can be a good source of bioactive compounds and can be attractive for the consumer in term of visual appearance and taste. In this work, [...] Read more.
The minimally processed industry is always looking for produce innovation that can satisfy consumer needs. Wild leafy vegetables can be a good source of bioactive compounds and can be attractive for the consumer in term of visual appearance and taste. In this work, Sisymbrium officinale (L.) Scop., commonly called hedge mustard, was grown in a greenhouse and evaluated as a potential leafy vegetable. Two wild populations, Milano (MI) and Bergamo (BG), were grown in peat substrate and harvested at the commercial stage for the minimally processing industry. Leaf pigments such as chlorophyll and carotenoids were determined as well as chlorophyll a fluorescence parameters. Total sugars, antioxidant compounds such as ascorbic acid, phenolic index, total phenols, anthocyanins, and nitrate were determined at harvest. Significant differences between wild populations were found in April with higher nitrate content in BG, 2865 mg/kg FW than in MI, 1770 mg/kg FW. The nitrate levels of S. officinale measured in the present study are significantly lower than the maximum NO₃ level allowed in other fresh leafy vegetables. Ascorbic acid measured in November was higher in MI compared BG with values of 54.4 versus 34.6 mg/100 g FW, respectively. The chlorophyll a fluorescence data showed that BG reached optimal leaf functionality faster than MI. Overall results indicated that Sisymbrium officinale (L.) Scop. can be suggested as a potential leafy vegetable for the minimally processed industry. Full article
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Open AccessArticle
Estimation of Ascorbic Acid in Intact Acerola (Malpighia emarginata DC) Fruit by NIRS and Chemometric Analysis
Horticulturae 2019, 5(1), 12; https://doi.org/10.3390/horticulturae5010012
Received: 10 December 2018 / Revised: 8 January 2019 / Accepted: 18 January 2019 / Published: 24 January 2019
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Abstract
Acerola fruit is one of the richest natural sources of ascorbic acid ever known. As a consequence, acerola fruit and its products are demanded worldwide for the production of health supplements and the development of functional products. However, the analytical determination of ascorbic [...] Read more.
Acerola fruit is one of the richest natural sources of ascorbic acid ever known. As a consequence, acerola fruit and its products are demanded worldwide for the production of health supplements and the development of functional products. However, the analytical determination of ascorbic acid is time-consuming and costly. In this study, we show a non-destructive, reliable, and fast method to measure the ascorbic acid content in intact acerola, using near-infrared spectroscopy (NIRS) associated with multivariate calibration methods. Models using variable selection by means of interval partial least squares (iPLS) and a genetic algorithm (GA) were tested. The best model for ascorbic acid content, based on the prediction performance, was the GA-PLS method with second derivative spectral pretreatment, with a root mean square error of cross-validation equal to 22.9 mg/100 g, root mean square error of prediction equal to 46.3 mg/100 g, ratio of prediction to deviation equal to 8.0, determination coefficient for calibration equal to 0.98 and determination coefficient for prediction equal to 0.96. The current methodology, using NIR spectroscopy and chemometrics, is a promising and rapid tool to determine the ascorbic acid content of intact acerola fruit. Full article
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Open AccessEditorial
Acknowledgement to Reviewers of Horticulturae in 2018
Horticulturae 2019, 5(1), 11; https://doi.org/10.3390/horticulturae5010011
Published: 23 January 2019
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Abstract
Rigorous peer-review is the corner-stone of high-quality academic publishing [...] Full article
Open AccessArticle
Hormonal Regulation of Early Fruit Development in European Pear (Pyrus communis cv. ‘Conference’)
Received: 18 December 2018 / Revised: 15 January 2019 / Accepted: 17 January 2019 / Published: 22 January 2019
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Abstract
European pear requires inter-cultivar cross-pollination by insects to develop fertilized fruits. However, some European pear cultivars such as ‘Conference’ naturally produce parthenocarpic seedless fruits. To better understand the hormonal regulation of fruit set and early fruit development in this European pear cultivar, the [...] Read more.
European pear requires inter-cultivar cross-pollination by insects to develop fertilized fruits. However, some European pear cultivars such as ‘Conference’ naturally produce parthenocarpic seedless fruits. To better understand the hormonal regulation of fruit set and early fruit development in this European pear cultivar, the phytohormone and polyamine profiles in ‘Conference’ flowers and fruits resulting from both fertilization and parthenocarpic processes were analyzed. The expression of genes involved in phytohormone metabolism and signaling were also investigated. Phytohormone profiles differed more at flower stage 3 days after treatment than in 15 day- and 30-day-old fruits in response to fertilization and parthenocarpy. An increase in auxins, abscisic acid, ethylene precursor, and spermine, and a decrease in putrescine were recorded in the fertilized flowers as compared to the parthenocarpic flowers. Fertilization also upregulated genes involved in gibberellin synthesis and down-regulated genes involved in gibberellin catabolism although the total gibberellin content was not modified. Moreover, exogenous gibberellin (GA3, GA4/7) and cytokinin (6BA) applications did not increase parthenocarpic induction in ‘Conference’ as observed in other European and Asian pear cultivars. We hypothesize that the intrinsic parthenocarpy of ‘Conference’ could be related to a high gibberellin level in the flowers explaining why exogenous gibberellin application did not increase parthenocarpy as observed in other pear cultivars and species. Full article
(This article belongs to the Special Issue Molecular, Genetic and Physiological Control of Fruit Quality)
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Open AccessArticle
Variable Pulsed Irrigation Algorithm (VPIA) to Reduce Runoff Losses under a Low-Pressure Lateral Move Irrigation Machine
Horticulturae 2019, 5(1), 10; https://doi.org/10.3390/horticulturae5010010
Received: 12 December 2018 / Revised: 15 January 2019 / Accepted: 18 January 2019 / Published: 22 January 2019
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Abstract
Due to restrictions and limitations on agricultural water worldwide, one of the most effective ways to conserve water in this sector is to reduce the water losses and improve irrigation uniformity. Nowadays, the low-pressure sprinkler has been widely used to replace the high-pressure [...] Read more.
Due to restrictions and limitations on agricultural water worldwide, one of the most effective ways to conserve water in this sector is to reduce the water losses and improve irrigation uniformity. Nowadays, the low-pressure sprinkler has been widely used to replace the high-pressure impact sprinklers in lateral move sprinkler irrigation systems due to its low operating cost and high efficiency. However, the hazard of surface runoff represents the biggest obstacle for low-pressure sprinkler systems. Most researchers have used the pulsing technique to apply variable-rate irrigation to match the crop water needs within a normal application rate that does not produce runoff. This research introduces a variable pulsed irrigation algorithm (VPIA) based on an ON–OFF pulsing technique to conserve irrigation water through (1) decreasing the runoff losses by considering the soil infiltration rate, surface storage capacity, and sprinkler wetting diameter; and (2) ensuring a high level of water distribution uniformity in the direction of machine movement. From a wide range of pulse numbers and widths tested applying a certain water depth to a sandy loam soil, the best solution that gives the lowest runoff and highest uniformity while delivering an acceptable water depth was selected. A MATLAB code was written to simulate the soil infiltration rate, the sprinkler application rate, and to apply the proposed algorithm. The simulation results showed a runoff reduction of at least 90.7% with a high level of distribution uniformity in the direction of movement while delivering the highest possible irrigation depth using the lowest number of pulses. Full article
(This article belongs to the Special Issue Water Management of Horticultural Crops)
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Open AccessArticle
Water-Related Variables for Predicting Yield of Apple under Deficit Irrigation
Received: 14 December 2018 / Revised: 1 January 2019 / Accepted: 15 January 2019 / Published: 16 January 2019
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Abstract
Predicting apple yield in relation to tree water use is important for irrigation planning and evaluation. The aim of the present study was to identify measurable variables related to tree water use that could predict final fruit yield of apple trees under different [...] Read more.
Predicting apple yield in relation to tree water use is important for irrigation planning and evaluation. The aim of the present study was to identify measurable variables related to tree water use that could predict final fruit yield of apple trees under different strategies of deficit irrigation. Adult ‘Gala’ and ‘Fuji’ apple trees were exposed to conventional irrigation (CI), delivering 100% of crop evapotranspiration; partial root zone drying (PRD), delivering 50% of CI water only on one alternated side of the root-zone; and continuous deficit irrigation (CDI), delivering 50% of CI water on both sides of the root-zone. Integrals of soil (SWDint) and leaf (LWSDint) water deficit along with growth and stomatal conductance (Gsint) were calculated across each season and used to estimate total conductance (GStree) and transpiration (Trtree) per tree, transpiration efficiency on a fruit (GRfruit/Tr) or tree (GRtrunk/Tr) growth basis, and transpiration productivity (Yield/Trtree). ‘Fuji’ trees had higher Yield/Trtree, but had lower GRtrunk/Tr and similar GRfruit/Tr compared to ‘Gala’ trees. In ‘Fuji’, CDI reduced yield, trunk growth, leaf hydration, and gas exchange, while in ‘Gala’, it did not reduce yield and gas exchange. In ‘Fuji’, a linear combination of GRtrunk/Tr, GRfruit/Tr, and Gstree contributed to predicting yield, with GRfruit/Tr explaining nearly 78% of the model variability. In ‘Gala’, a linear combination of LWSDint and Gstree contributed to predicting yield, with Gstree explaining over 79% of the model variability. These results indicate that measuring tree water status or water use may help predict final apple yields only in those cultivars like ‘Gala’ that cannot limit dehydration by closing stomates because of carbon starvation. In more vigorous cultivars like ‘Fuji’, transpiration efficiency based on fruit growth can be a powerful predictor of final yields. Full article
(This article belongs to the Special Issue Abiotic Stress Effects on Performance of Horticultural Crops)
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Open AccessReview
Irrigation of Greenhouse Crops
Received: 29 November 2018 / Revised: 23 December 2018 / Accepted: 29 December 2018 / Published: 15 January 2019
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Abstract
Precision agricultural greenhouse systems indicate considerable scope for improvement of irrigation management practices, since growers typically irrigate crops based on their personal experience. Soil-based greenhouse crop irrigation management requires estimation on a daily basis, whereas soilless systems must be estimated on an hourly [...] Read more.
Precision agricultural greenhouse systems indicate considerable scope for improvement of irrigation management practices, since growers typically irrigate crops based on their personal experience. Soil-based greenhouse crop irrigation management requires estimation on a daily basis, whereas soilless systems must be estimated on an hourly or even shorter interval schedule. Historically, irrigation scheduling methods have been based on soil or substrate monitoring, dependent on climate or time with each having both strengths and weaknesses. Recently, plant-based monitoring or plant reflectance-derived indices have been developed, yet their potential is limited for estimating the irrigation rate in order to apply proper irrigation scheduling. Optimization of irrigation practices imposes different irrigation approaches, based on prevailing greenhouse environments, considering plant-water-soil relationships. This article presents a comprehensive review of the literature, which deals with irrigation scheduling approaches applied for soil and soilless greenhouse production systems. Irrigation decisions are categorized according to whether or not an automatic irrigation control has the ability to support a feedback irrigation decision system. The need for further development of neural networks systems is required. Full article
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Open AccessReview
Response of Mediterranean Ornamental Plants to Drought Stress
Received: 12 December 2018 / Revised: 3 January 2019 / Accepted: 3 January 2019 / Published: 14 January 2019
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Abstract
Ornamental plants use unique adaptive mechanisms to overcome the negative effects of drought stress. A large number of species grown in the Mediterranean area offer the opportunity to select some for ornamental purposes with the ability to adapt to drought conditions. The plants [...] Read more.
Ornamental plants use unique adaptive mechanisms to overcome the negative effects of drought stress. A large number of species grown in the Mediterranean area offer the opportunity to select some for ornamental purposes with the ability to adapt to drought conditions. The plants tolerant to drought stress show different adaptation mechanisms to overcome drought stress, including morphological, physiological, and biochemical modifications. These responses include increasing root/shoot ratio, growth reduction, leaf anatomy change, and reduction of leaf size and total leaf area to limit water loss and guarantee photosynthesis. In this review, the effect of drought stress on photosynthesis and chlorophyll a fluorescence is discussed. Recent information on the mechanisms of signal transduction and the development of drought tolerance in ornamental plants is provided. Finally, drought-induced oxidative stress is analyzed and discussed. The purpose of this review is to deepen our knowledge of how drought may modify the morphological and physiological characteristics of plants and reduce their aesthetic value—that is, the key parameter of assessment of ornamental plants. Full article
(This article belongs to the Special Issue Abiotic Stress Effects on Performance of Horticultural Crops)
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Open AccessArticle
A Preliminary Assessment of Horticultural Postharvest Market Loss in the Solomon Islands
Received: 29 November 2018 / Revised: 18 December 2018 / Accepted: 4 January 2019 / Published: 10 January 2019
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Abstract
Honiara’s fresh horticultural markets are a critical component of the food distribution system in Guadalcanal, Solomon Islands. Most of the population that reside in Honiara are now dependent on the municipal horticultural market and a network of smaller road-side markets to source their [...] Read more.
Honiara’s fresh horticultural markets are a critical component of the food distribution system in Guadalcanal, Solomon Islands. Most of the population that reside in Honiara are now dependent on the municipal horticultural market and a network of smaller road-side markets to source their fresh fruits and vegetables. Potentially poor postharvest supply chain practice could be leading to high levels of postharvest loss in Honiara markets, undermining domestic food security. This study reports on a preliminary assessment of postharvest horticultural market loss and associated supply chain logistics at the Honiara municipal market and five road-side markets on Guadalcanal Island. Using vendor recall to quantify loss, we surveyed a total of 198 vendors between November 2017 and March 2018. We found that postharvest loss in the Honiara municipal market was 7.9 to 9.5%, and that road-side markets incurred 2.6 to 7.0% loss. Based on mean postharvest market loss and the incidence of individual vendor loss, Honiara’s road-side market system appears to be more effective in managing postharvest loss, compared to the municipal market. Postharvest loss was poorly correlated to transport distance, possibly due to the inter-island and remote intra-island chains avoiding high-perishable crops. Spatial mapping of postharvest loss highlighted a cohort of villages in the western and southern parts of the main horticultural production region (i.e., eastern Guadalcanal) with atypically high levels of postharvest loss. The potential importance of market-operations, packaging type, and mode of transport on postharvest market loss, is further discussed. Full article
(This article belongs to the Special Issue Marketing Strategies of Horticultural Production Chain)
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Open AccessArticle
How Water Quality and Quantity Affect Pepper Yield and Postharvest Quality
Received: 29 November 2018 / Revised: 24 December 2018 / Accepted: 2 January 2019 / Published: 7 January 2019
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Abstract
There are gaps in our knowledge of the effects of irrigation water quality and amount on yield and postharvest quality of pepper fruit (Capsicum annuum L.). We studied the effects of water quality and quantity treatments on pepper fruits during subsequent simulated [...] Read more.
There are gaps in our knowledge of the effects of irrigation water quality and amount on yield and postharvest quality of pepper fruit (Capsicum annuum L.). We studied the effects of water quality and quantity treatments on pepper fruits during subsequent simulated storage and shelf-life. Total yield decreased with increasing water salinity, but export-quality yield was not significantly different in fruits irrigated with water of either 1.6 or 2.8 dS/m, but there was a 30–35% reduction in export-quality yield following use of water at 4.5 dS/m. Water quantity hardly affected either total or export-quality yield. Water quality but not quantity significantly affected fruit weight loss after 14 days at 7 °C plus three days at 20 °C; irrigation with water at 2.8 dS/m gave the least weight loss. Fruits were significantly firmer after irrigation with good-quality water than with salty water. The saltier the water, the higher was the sugar content. Vitamin C content was not affected by water quality or quantity, but water quality significantly affected antioxidant (AOX) content. The highest AOX activity was found with commercial quality water, the lowest with salty water. Pepper yield benefited by irrigation with fresh water (1.6 dS/m) and was not affected by water quantity, but post-storage fruit quality was maintained better after use of moderately-saline water (2.8 dS/m). Thus, irrigation water with salinity not exceeding 2.8 dS/m will not impair postharvest quality, although the yield will be reduced at this salinity level. Full article
(This article belongs to the Special Issue Abiotic Stress Effects on Performance of Horticultural Crops)
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Open AccessArticle
Precision Crop Load Management of Apple (Malus x domestica Borkh.) without Chemicals
Received: 15 November 2018 / Revised: 20 December 2018 / Accepted: 21 December 2018 / Published: 28 December 2018
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Abstract
Fruit thinning is an important management practice in commercial apple production. The standard industry practice for crop load management in many countries is based on bloom and/or post-bloom chemical thinning (CT) followed up with hand thinning. However, the response to CT is unpredictable [...] Read more.
Fruit thinning is an important management practice in commercial apple production. The standard industry practice for crop load management in many countries is based on bloom and/or post-bloom chemical thinning (CT) followed up with hand thinning. However, the response to CT is unpredictable and there is an increasing awareness of the environmental impact of many chemicals. Hence there is a need to find alternate environmentally acceptable methods for managing crop load. Artificial bud extinction (ABE), a thinning method that imitates natural bud extinction by manually removing buds before bud break, has been suggested as a potential tool to replace chemical thinning, but there have been no studies comparing ABE and chemical thinning. Trials were established in Tasmania, Australia to determine how ABE technology compares with best practice CT programs in terms of yield, fruit quality, and cost of implementation. Results from these trials demonstrated consistent fruit set of both Gala and Fuji apple under ABE management compared with conventional management. Fruit weight was increased in all ABE treatments from 5% up to 38%. The four studies presented here have demonstrated that ABE is a feasible alternative to chemical thinning, improving reliability of crop load management with increased predictability of fruit size and yield. Trees are significantly thinned before flowering, controlling biennial bearing. In addition, bud position is optimised, fruit is well spaced and light distribution into the canopy is enhanced. In terms of costs, implementation of ABE is comparable to managing crop load with CT programs but has the advantage that crop load management costs reduce in subsequent years after the initial tree set-up. ABE is also suitable for use in organic apple orchards. Full article
(This article belongs to the Special Issue Food Safety Pertinent to Fresh Produce)
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Open AccessArticle
Estimation of Citrus Maturity with Fluorescence Spectroscopy Using Deep Learning
Received: 26 November 2018 / Revised: 19 December 2018 / Accepted: 21 December 2018 / Published: 26 December 2018
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Abstract
To produce high-quality citrus, the harvest time of citrus should be determined by considering its maturity. To evaluate citrus maturity, the Brix/acid ratio, which is the ratio of sugar content or soluble solids content to acid content, is one of the most commonly [...] Read more.
To produce high-quality citrus, the harvest time of citrus should be determined by considering its maturity. To evaluate citrus maturity, the Brix/acid ratio, which is the ratio of sugar content or soluble solids content to acid content, is one of the most commonly used indicators of fruit maturity. To estimate the Brix/acid ratio, fluorescence spectroscopy, which is a rapid, sensitive, and cheap technique, was adopted. Each citrus peel was extracted, and its fluorescence value was measured. Then, the fluorescent spectrum was analyzed using a convolutional neural network (CNN). In fluorescence spectroscopy, a matrix called excitation and emission matrix (EEM) can be obtained, in which each fluorescence intensity was recorded at each excitation and emission wavelength. Then, by regarding the EEM as an image, the Brix/acid ratio of juice from the flesh was estimated via performing a regression with a CNN (CNN regression). As a result, the Brix/acid ratio absolute error was estimated to be 2.48, which is considerably better than the values obtained by the other methods in previous studies. Hyperparameters, such as depth of layers, learning rate, and the number of filters used for this estimation, could be observed using Bayesian optimization, and the optimization contributed to the high accuracy. Full article
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Open AccessArticle
Postharvest UV-C Treatment, Followed by Storage in a Continuous Low-Level Ethylene Atmosphere, Maintains the Quality of ‘Kensington Pride’ Mango Fruit Stored at 20 °C
Received: 3 December 2018 / Revised: 18 December 2018 / Accepted: 21 December 2018 / Published: 25 December 2018
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Abstract
Mature green ‘Kensington Pride’ mangoes (Mangifera indica L.) were treated with a short-term UV-C light at four different intensities (0, 4.0, 8.3 and 11.7 kJ m−2). After treatment, mangoes were stored for 12 d in air (<0.005 μL L−1 [...] Read more.
Mature green ‘Kensington Pride’ mangoes (Mangifera indica L.) were treated with a short-term UV-C light at four different intensities (0, 4.0, 8.3 and 11.7 kJ m−2). After treatment, mangoes were stored for 12 d in air (<0.005 μL L−1 ethylene) or 0.1 μL L−1 ethylene at 20 °C and 100% relative humidity (RH). Weight loss, peel colour, firmness, ethylene production, respiration rate, total soluble solids (TSS), titratable acidity (TA), total chlorophyll content, total phenolic content (TPC) and total antioxidant activity were assessed at 3-d intervals. The results showed that UV-C treatment delayed skin degreening, reduced endogenous ethylene production, suppressed respiration rate and lowered chlorophyll content compared to untreated control fruit. Fruit treated with UV-C had significantly higher TPC and total antioxidant activity at the end of the storage period than untreated fruits for both storage atmospheres. In addition, UV-C treated fruits remained significantly firmer than untreated fruits. UV-C treatment significantly affected TSS and TA levels in different ways. Storage of fruits in 0.1 μL L−1 ethylene significantly affected fruit firmness, respiration rate and ethylene production, while other fruit quality parameters were similar to fruit stored in air. These results indicated that UV-C irradiation could be used as an effective and rapid method to extend the postharvest life of mature green mangoes without adversely affecting certain quality attributes in the presence of low-level ethylene during storage. Full article
(This article belongs to the Special Issue Molecular, Genetic and Physiological Control of Fruit Quality)
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