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  • Author or Editor: Youbin Zheng x
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Electrolytically generated copper is increasingly used to control diseases and algae in the greenhouse industry. However, there is a shortage of information regarding appropriate management strategies for copper in ornamental crop production. The objectives of this study were to characterize the response of three ornamental crops (Dendranthema ×grandiflorum L. `Fina', Rosa ×hybrida L. `Lavlinger', Pelargonium ×hortorum L. `Evening Glow') to different solution levels of Cu2+ (ranging from 0.4 to 40 μm) and to determine the critical levels above which toxic responses became apparent. The following measurements were used to assess the treatments: leaf chlorophyll fluorescence (Fv/Fm), leaf chlorophyll content, and visible injury of leaf and root. Excessive copper reduced plant root length, root dry weight, total dry weight, root to shoot ratio, leaf area, and specific leaf area in all three species. The critical solution level of Cu2+ that resulted in significantly reduced plant dry weight for chrysanthemum was 5 μm; for miniature rose, 2.4; and for geranium, 8 μm. Plant visible root injury was a more sensitive and reliable copper toxicity indicator than visible leaf injury, leaf chlorophyll content, Fv/Fm, or leaf and stem copper content. Generally, all the species exhibited some sensitivity to Cu2+ in solution culture, with chrysanthemum and miniature rose being most sensitive and geranium being least sensitive. Caution should be taken when applying copper in solution culture production systems.

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Pot gerbera (Gerbera jamesonii Var. `Shogun') plants were subirrigated with one of four nutrient solutions (10, 25, 50, and 100% of full strength) in order to determine whether currently used commercial nutrient solution concentrations can be reduced without negative impact on crop production. Nutrient concentration levels did not affect leaf area, flower number and appearance, and plant total dry weight. There were no significant differences in leaf chlorophyll content between the plants that received the 50 and 100% strength nutrient solutions. It is concluded that nutrient solution concentrations typically used in commercial greenhouse, for pot gerbera production, can be safely reduced by at least 50% without adversely affecting crop production. Nutrients accumulated in the top section of the growth substrate under all treatment levels; however, no phytotoxic effect was observed. Fertilizer inputs were reduced in the 50%, 25%, and 10% treatments by 54%, 75%, and 90% respectively. After 4 weeks recirculating, the quality of the nutrient solutions was still within acceptable limits.

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To determine whether currently used commercial nutrient solution concentrations can be reduced during the final stage (last 4 to 5 weeks) of production of potted gerbera (Gerbera jamesonii `Shogun') under recirculating subirrigation conditions, plants were grown under one of four nutrient levels (10%, 25%, 50%, and 100% of full strength). Nutrient concentration levels did not affect leaf area, flower number and appearance, and plant total dry weight. There were no significant differences in the greenness (as measured by SPAD meter) of leaves from plants that received the 50% and 100% strength nutrient solutions. However, leaves from plants that received the 10% and 25% strength solution showed significantly less greenness than that of the plants that received 50% and 100% strength nutrient solutions. There were interveinal chlorosis symptoms on the younger leaves of some plants in the 10% and 25% strength nutrient treatments. It is suspected that this interveinal chlorosis was due to iron (Fe) deficiency caused by the increased substrate pH. It is concluded that the nutrient solution concentrations typically used for potted gerbera production in commercial greenhouses at the final stage (4 to 5 weeks) under recirculating subirrigation conditions, can be safely reduced by at least 50% without adversely affecting crop production. Nutrient salts accumulated in the top section of the growth substrate under all treatments levels; however, no phytotoxic effects were observed. No differences in water use (141 mL per plant per day) were observed amid the various nutrient levels. Fertilizer inputs were reduced in the 50%, 25%, and 10% treatments by 54%, 75%, and 90% respectively, relative to the 100% treatment. After 4 weeks under recirculating conditions, the qualities of the nutrient solutions were still within acceptable limits.

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In greenhouse ornamental crop production, bedding plants grown below high densities of hanging baskets (HBs) tend to be of lower quality. Hanging basket crops can decrease the red to far red ratio (R:FR) of the growing environment below; however, the extent to which decreased R:FR affects plant morphology and flowering of the lower-level crops is unknown. The present study examined effects of R:FR on morphology and flowering of marigold ‘Antigua Orange’ (Tagetes erecta), petunia ‘Duvet Red’ (Petunia ×hybrida), calibrachoa ‘Kabloom Deep Blue’ (Calibrachoa ×hybrida), and geranium ‘Pinto Premium Salmon’ (Pelargonium ×hortorum). Five R:FR light treatments were provided ranging from R:FR 1.1 (representing unfiltered sunlight) to R:FR 0.7 (representing shaded conditions under HBs) using light-emitting diodes (LEDs) in growth chambers, each with identical photosynthetically active radiation (PAR) (400–700 nm) and FR added to achieve the target R:FR ratio. Two experiments using the same R:FR treatments were conducted with day/night temperature regimes of 20 °C/18 °C and 25 °C/21 °C, respectively. In the second experiment, a fluorescent light treatment was included. The results of the second experiment were more dramatic than the first, where reducing R:FR from 1.1 to 0.7 increased height by 11%, 22%, and 32% in marigold, petunia, and calibrachoa, respectively, and increased petiole length in geranium by 10%. Compared with R:FR 1.1, the R:FR 0.7 shortened the time to the appearance of first flower bud by 2 days in marigold, whereas flowering was minimally affected in other species. Compared with pooled data from the LED treatments, fluorescent light increased relative chlorophyll content for all species, reduced height in marigold, petunia, calibrachoa, and geranium by 26%, 67%, 60%, and 48%, and reduced stem dry weight by 28%, 39%, 21%, and 31%, respectively. The differences in morphology observed under fluorescent light compared with LED R:FR treatments indicate that light quality manipulation is a potential alternative to chemical growth regulators in controlled environments such as greenhouses and growth chambers.

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To determine the optimum feeding nutrient solution concentrations for the production of potted miniature roses (Rosa chineersis minima ‘Fall Festival’) under recirculating subirrigation conditions, plants were grown under four different nutrient solution concentrations [25%, 50%, 75%, and 100% of the full strength with an electrical conductivity (EC) of 1.756 dS·m−1]. Nutrient solution concentrations affected the stem, root, and plant total dry weight and flower and branch number. Under the 75% strength nutrient solution, these growth parameters were equal to or better than the 100% strength solution. No difference was detected in the chlorophyll content of leaves from plants that received the 50%, 75%, and 100% strength solutions during the experiment but at Day 35; only the 25% treatment had significantly lower leaf chlorophyll content than the other treatments. There were no treatment effects on the measured total foliar nutrient contents [except potassium (K)] of plants under the 75% strength solution compared with those under the 100% treatment, but nitrogen (N), phosphorus (P), and/or iron (Fe) of plants under the 25% strength solutions were below that of the acceptable range. Interveinal chlorosis and/or reddish leaves and branches were also apparent in plants under the 25% and 50% strength solutions. It is suspected that these are symptoms of N, P, and Fe deficiencies caused by the reduced nutrient solution concentrations and increased pH of the growing substrate. There were significant depletions of N and P nutrients in the 25% and 50% strength solutions at the end of the experiment, which was consistent with visual symptoms and deficiencies. Nutrient salts accumulated in the top section of the growing substrate under all treatments, but no phytotoxic effects were observed. The EC values for the top third of the growing substrate were much higher than those of the bottom two-thirds. EC for the top layer of the 100% treatment exhibited a fourfold increase compared with the bottom layer of that treatment. The NO3 , K, magnesium, and calcium for the top layer of the 100% treatment were 235%, 149%, 287%, and 245%, respectively, higher compared with the bottom layer of the 100% treatment. It was concluded that the nutrient solution concentrations typically used for potted miniature rose production in most of the Canadian greenhouses under recirculating subirrigation conditions can be safely reduced to 75% and produce better plants.

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Short campanula (Campanula portenschlagiana ‘PGM Get MEE’®) stock plants present a difficulty in machine-harvesting of cuttings. Light adjustment may be an effective approach to mediate plant elongation. Two experiments were performed to 1) investigate whether short-term (five weeks) daily 24-h dynamic lighting (DL) with red and blue light-emitting diodes (LEDs) can promote elongation without inducing flowering, and 2) explore whether DL can be used to modify stock plant morphology to improve the cutting quality and rooting success in a controlled environment. Two lighting treatments were used: concurrent lighting (CL) with red (85%) and blue (15%) LEDs (RB) at 100 µmol·m−2·s−1 and DL with red (170 µmol·m−2·s−1), blue (30 µmol·m−2·s−1), and RB (100 µmol·m−2·s−1) LEDs sequentially at three different lighting stages, respectively, in both experiments. In Expt. 1, at final harvest of stock plants, the side branches were longer under DL compared with CL, but the five (= 2 + 2 + 1) weeks of 24-h daily lighting resulted in visible flower buds under both treatments. Based on the results of Expt. 1, a second experiment (Expt. 2) was conducted with the same cultivar and experimental conditions, but with a shorter photoperiod (10 h·d−1) for 11 (= 8 + 2 + 1) weeks. In Expt. 2, at final harvest, DL compared with CL caused more upright side branches, and reduced the dry biomass of side branches with one branching order and leaf chlorophyll content. However, the harvested cutting quality and rooting success were similar between both treatments. In both experiments, side branch number under DL was greater compared with CL at the end of the first lighting stage. Stock plants under DL were taller from the second lighting stage on to final harvest compared with CL, and the final heights of stock plants under DL met the target for machine-harvest in both experiments. Therefore, if the lighting strategy is further optimized, DL can potentially benefit controlled-environment production of campanula cuttings.

Open Access

Low natural daily light integrals (DLIs) are a major limiting factor for greenhouse production during darker months (e.g., October to February in Canada). Supplemental lighting (SL) is commonly used to maintain crop productivity and quality during these periods, particularly when the supply chain demands consistent production levels year-round. What remains to be determined are the optimum SL light intensities (LIs) for winter production of a myriad of different commodities. The present study investigated the growth and yield of sunflower (Helianthus annuus L., ‘Black oil’), kale (Brassica napus L., ‘Red Russian’), arugula (Eruca sativa L.), and mustard (Brassica juncea L., ‘Ruby Streaks’), grown as microgreens, in a greenhouse under SL light-emitting diode (LED) photosynthetic photon flux density (PPFD) levels ranging from 17.0 to 304 μmol·m−2·s−1 with a 16-hour photoperiod (i.e., supplemental DLIs from 1.0 to 17.5 mol·m−2·d−1). Crops were sown in a commercial greenhouse near Hamilton, ON, Canada (lat. 43°14′N, long. 80°07′W) on 1 Feb. 2018, and harvested after 8, 11, 12, and 12 days, resulting in average natural DLIs of 6.5, 5.9, 6.2, and 6.2 mol·m−2·d−1 for sunflower, kale, arugula, and mustard, respectively. Corresponding total light integrals (TLIs) ranged from 60 to 188 mol·m−2 for sunflower, 76 to 258 mol·m−2 for kale, 86 to 280 mol·m−2 for arugula, and 86 to 284 mol·m−2 for mustard. Fresh weight (i.e., marketable yield) increased asymptotically with increasing LI and leaf area increased linearly with increasing LI, in all genotypes. Hypocotyl length of mustard decreased and hypocotyl diameter of sunflower, arugula, and mustard increased with increasing LI. Dry weight, robust index, and relative chlorophyll content increased and specific leaf area decreased in kale, arugula, and mustard with increasing LI. Commercial microgreen greenhouse growers can use the light response models described herein to predict relevant production metrics according to the available (natural and supplemental) light levels to select the most appropriate SL LI to achieve the desired production goals as economically as possible.

Open Access

Intercropping can increase land use efficiency in high tunnel crop production, but it may also lead to decreases in yield and quality of main crops due to the potential competition for resources. This study evaluated the agronomic viability of intercropping snow pea (Pisum sativum L., ‘Ho Lan Dou’) with cherry tomato (Solanum lycopersicum L. var. cerasiforme ‘Sarina hybrid’) without additional inputs of water and fertilizers on peas in an organic high tunnel production system under Southern Ontario climate conditions in Guelph, Ontario, Canada (lat. 43.5 °N, long. 80.2 °W) during 2015 and 2016. In each 80-cm-wide bed, the tomato crops were planted alternately in double rows spaced 30 cm apart, with in-row spacing of 110 cm, which resulted in a planting density of ≈24,000 plants/ha. The snow pea seeds were sown between the tomato plants (i.e., within the same beds as tomatoes) in holes (two seeds per hole), with four rows in each bed and in-row holes spaced 10 cm and at least 25 cm away from the tomato plants, which resulted in a seeding rate of ≈650, 000 seeds/ha. The same amount of water or fertilizer was applied to the intercropping and nonintercropping plots based on the needs of the cherry tomato plants. Plant growth, fruit yield, and quality were compared between tomato plants with and without intercropping. Intercropping with snow peas did not affect total marketable fruit yield, unmarketable fruit percentage, fruit quality traits (e.g., individual fruit weight, soluble solids content, dry matter content, and postharvest water loss), or early-stage plant growth of the cherry tomato. Therefore, it is at least an agronomical possibility to intercrop snow peas with cherry tomatoes on the same beds without additional inputs of water and fertilizer on snow peas in an organic high tunnel system. The additional yield of pea shoots or pods in the intercropping treatment also increased economic gross returns in the high tunnels, although the economic net return might vary with the costs of seeds and labor involved in snow pea growing.

Open Access

Hydrogen peroxide (H2O2) is an oxidizing agent used to disinfect recirculated irrigation water during the production of organic crops under controlled environmental systems (e.g., greenhouses). To characterize the phytotoxic effects and define a concentration threshold for H2O2, three microgreen species [arugula (Brassica eruca ssp. sativa), radish (Raphanus sativus), and sunflower (Helianthus annuus ‘Black Oil’)], and three lettuce (Lactuca sativa) cultivars, Othilie, Xandra, and Rouxai, were foliar sprayed once daily with water containing 0, 25, 50, 75, 100, 125, 150, or 200 mg·L−1 of H2O2 from seed to harvest under greenhouse conditions. Leaf damage was assessed at harvest using two distinct methods: 1) the percentage of damaged leaves per tray and 2) a damage index (DI). Applied H2O2 concentrations, starting from 25 mg·L−1, increased the percentage of damaged leaves in every species except ‘Black Oil’ sunflower, which remained unaffected by any applied concentration. Symptoms of leaf damage manifested in similar patterns on the surface of microgreen cotyledons and lettuce leaves, while mean DI values and extent of damage were unique to each crop. Fresh weight, dry weight, and leaf area of all crops were not significantly affected by daily H2O2 spray. Identifying how foliar H2O2 damage manifests throughout the crop, as well at individual cotyledon or leaf surfaces, is necessary to establish an upper concentration threshold for H2O2 use. On the basis of the aforementioned metrics, maximum recommended concentrations were 150 mg·L−1 (radish), 100 mg·L−1 (arugula) for microgreens and 125 mg·L−1 (‘Othilie’), 75 mg·L−1 (‘Rouxai’), and 125 mg·L−1 (‘Xandra’) lettuce.

Open Access

To effectively manage crop production in a greenhouse, it is essential to understand the natural light environment and physiological responses of the plants to light. This study investigated the dynamics of photosynthetic photon flux densities (PPFD) and light quality within the canopies of greenhouse-grown eggplant (Solanum melongena) and the photosynthetic capacities of leaves at different locations within the canopies. The light environment was quantified at 0.2-m intervals within (intra-canopy) and adjacent to (extra-canopy) the crop canopy on both sunny and cloudy days within a commercial greenhouse located in Leamington, Ontario, Canada. Our results indicated a linear decline in extra-canopy PPFD on both sunny and cloudy days, but an exponential decrease in intra-canopy PPFD. The intra-canopy PPFD decreased by 91% and 76% between 0 m and 0.4 m from the canopy apex on sunny and cloudy days, respectively. The lower canopy (0.6–1.2 m) light spectrum consisted largely of far-red light, equal amounts of red light and green light, with a lower percentage of blue light. Parameters derived from leaf-level light response curves indicated that the light-saturated net carbon exchange rate, light saturation point, and light compensation point decreased as the distance from canopy apex increased, whereas quantum yield was unaffected. Thus, leaves in the lower canopy were less efficient at using high PPFD, but they displayed no deterioration of photosynthetic machinery. Based solely on photosynthetic capabilities, leaves between 0 and 1.0 m from the canopy apex should not be removed to decrease the total plant sink strength.

Open Access