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  • Author or Editor: Martine Dorais x
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In order to improve fruit quality under the Northern climatic growing conditions prevailing in Quebec, Canada (lat. 47°N, long. 71°W), a greenhouse tomato (Lycopersicon esculentum Mill. cv. Blitz) spring production experiment was conducted using several irrigation regime and electrical conductivity (EC) levels. The irrigation regime treatments were a function of the global solar radiation, with three thresholds applied to each EC treatment. The irrigation thresholds (KJ·m–2) were 1) 468, 2) 540, and 3) 612. Two EC treatments were used: 1) control EC (2.0 to 3.5 mS·cm–1) and 2) 30% higher EC than the control (2.6 to 4.6 mS·cm–1), which was raised by adding NaCl to 12 mmol·L–1. Plant water potential in summer and in the fall and plant growth after 6 months were not affected by irrigation or EC treatments. Raising the EC increased the Na content of reproductive and vegetative parts and decreased the N concentration of the vegetative parts. The highest EC improved fruit quality by reducing the incidence of fruit cracking. Although marketable yields were not affected by EC (P = 0.09) or irrigation regime (P = 0.08) treatments, higher EC during March to September increased (P ≤ 0.01) the proportion of Class 2 fruit by reducing fruit size.

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Organically grown greenhouse sweet pepper crops, as is the case with most year-around greenhouse crops, rely on pre-grown transplants. Production of adequately balanced (source and sink strength potential) healthy organic sweet pepper transplants is a challenge and is often related to early and total harvested yields. Liquid and/or solid organic fertilizers for greenhouse sweet pepper transplants were compared with a conventional liquid fertilizer. Transplants were grown under greenhouse conditions and inoculated, or not, with a beneficial microbial agent, Trichoderma harzianum Rifai, strain KRL-AG2 (Rootshield®). Medium respiration (CO2 efflux) and fluorescein diacetate (FDA) hydrolysis analysis showed a higher microbial activity in the liquid organic fertilizer treatment. Higher microbial activity was observed after 10 weeks than at 5 weeks after transplanting. Transplant development was greater in the liquid conventional fertilizer treatment compared with the two organic treatments. Transplants that received liquid organic fertilizer had greater development compared with transplants that only received water in addition to the initial solid fertilizer. Organic amendment mineralization did not completely fulfill transplant nutrient requirement compared with conventional transplants. Solid fertilization in the growing medium affected plant growth during the first 5 weeks but not after 10 weeks after transplanting. Solid and liquid organic fertilizers at a higher concentration should be provided to reach a similar transplant development because conventional seedlings or other slow-release sources of solid amendments should be added to the growing medium to keep an adequate and constant nutrient release. Providing a beneficial agent to the organic growing medium increased its biological activity but had no effect on seedling growth during this study. Solid organic fertilization (1600 mL·m−3 of shrimp meal with 50 mL·m−3 of kelp meal) combined with an organic liquid fertilization should be used in combination with inoculation with T. harzianum to obtain high-quality organic sweet pepper transplants.

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Pythium root rot, caused by Pythium ultimum, is responsible for important losses in geranium plant production, mainly as a result of the decrease in the plant overall quality. An organic production system for geranium plants based on fertilization using a filtered suspension of dehydrated hen manure was compared with a conventional fertilization system to evaluate their tolerance to root disease. Under typical greenhouse conditions, geranium plants were inoculated with a suspension of Pseudomonas putida, Trichoderma atroviride, a mixture of both or with Trichoderma harzianum, and a commercially available product, Rootshield®, 1 and 4 weeks after planting. Four weeks after the first inoculation, Pseudomonas putida and Trichoderma atroviride stimulated plant growth (shoot and root dry weight) compared with the control regardless of the fertilization. The results also showed that the colonization of geranium roots by Pythium spp. was significantly lower for organically grown plants for all treatments compared with the inoculated control under conventional fertilization. Inoculation with T. atroviride under conventional fertilization was the only treatment that did not significantly reduce root colonization by Pythium spp. compared with the conventional control. For both organically and conventionally grown plants, the coinoculation with both P. putida and T. atroviride resulted in the weakest colonization of roots by the pathogen. The inoculation of P. putida, T. atroviride, and the mixture of the bacterium and the fungus also significantly increased the fresh and dry weight of roots regardless of the fertilization used. All microorganism treatments in conventionally grown plants significantly increased the fresh and dry weight of the shoot compared with the control.

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Yield of greenhouse tomatoes has greatly increased during the past decade due to the development of more-productive cultivars and to the use of new technologies, such as supplemental lighting and CO2 enrichment. Under high PPF and p[CO2], however, the capacity of tomato plants to use supplemental energy and CO2 decreases. Our project aimed at determining the limits of photosynthetic capacity of tomato plants under supplemental lighting (HPS lamps, 100 μmol·m–2·s–1, photoperiod of 14 to 17 h) and high p[CO2] (900 ppm). The following measurements were made on the 5th and the 10th leaves of tomato plants at regular intervals from November to May: diurnal changes in net (Pn) and maximum (Pmax) photosynthetic rate, Chla fluorescence of dark-adapted and no dark-adapted leaves, and the soluble sugars and starch contents of the 5th and 10th leaves. Changes in global radiation from 250 W/m2 in winter to about 850 W/m2 in spring resulted in Pn increases of 45% and 42% in the 5th and 10th leaves, respectively. During the winter period, Pmax was higher than Pn, suggesting that leaves were not at maximum photosynthetic capacity. In the spring, no difference was found between Pmax and Pn. Sucrose concentration in leaves increased progressively up to a maximum of 12-h photoperiod, while hexoses remained constant. The Fv/Fm ratio did not vary during winter, but significantly decreased during spring due to photoinhibition. Increases in global radiation during spring resulted in lower photosynthetic rates, higher fluorescence, and starch accumulation in leaves. Data will be discussed in terms of crop efficiency and yield.

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Ongoing research on organic growing media for greenhouse tomato production is driven by the constant changes in the quality, stability, and form of the organic byproducts used in the manufacturing of these media. This study was undertaken to determine appropriate irrigation set points for a sawdust–peat mix (SP) under development given that the performance of this substrate appeared to be strongly dependent on appropriate irrigation management. A greenhouse tomato experiment was conducted to compare different irrigation management approaches for a SP substrate in the spring and summer. Using preliminary measurements from an initial experiment (Expt. 1), different irrigation strategies for the SP substrate were compared in a second experiment (Expt. 2): 1) a variable irrigation regime using a timer control (with frequency adjusted as a function of irradiance); 2) tensiometer control at –1.5 kPa; and 3) two constant substrate water potential devices: –1.1 kPa and –0.9 kPa. An irrigation timer/controller using solar radiation input was used with a rockwool control (RC) substrate. Measurements of plant activity [photosynthesis rate and stomatal conductance (g S)], substrate physical and chemical properties, biomass, and yield were obtained. For all irrigation strategies, results indicated that 10% to 20% higher photosynthesis rates and g S values were obtained with the SP substrate compared with RC. Data indicated that moderate drying conditions (matric potential ranging from –2.2 kPa to –1.5 kPa in Expt. 1 and Expt. 2, respectively) relative to container capacity (–0.6 kPa) were beneficial for improving plant photosynthetic activity and allowed the highest yields for the SP substrate. Variable irrigation management showed higher levels of plant activity than constant watering and increased the oxygen concentration in the substrate by ≈2% in absolute value relative to the constant water potential device. Lower CO2 and N2O levels were also observed with the variable irrigation strategy. On the other hand, maximum nutrient solution savings were achieved with the constant matric potential devices (8% to 31% relative to the RC). This study showed high productivity potential for the SP substrate with suitable irrigation management. Replacing conventional growing media with organic waste-based products using an appropriate irrigation strategy may help to increase the sustainability of the greenhouse industry.

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Ethylene accumulation increases after harvest and culminates in needle abscission in balsam fir [Abies balsamea (L.) Mill.]. We hypothesize that water deficit induces ethylene evolution, thus triggering abscission. The purpose of this research was to investigate the role of temperature and humidity on postharvest needle abscission in the presence and absence of exogenous ethylene and link vapor pressure deficit (VPD) to postharvest needle abscission in balsam fir. In the first experiment, branches were exposed to 30%, 60%, or 90% humidity while maintained at 19.7 °C (VPD of 1.59, 0.91, or 0.23 kPa, respectively); in the second experiment, branches were exposed to 5, 15, or 25 °C (VPD of 0.35, 0.68, or 1.26 kPa, respectively) while maintained at 60% relative humidity. Needle retention duration, average water use, xylem pressure potential relative water content, and ethylene evolution were response variables. Reducing water loss or xylem tension by changing temperature or humidity effectively delayed needle abscission, although the 90% humidity treatment had the most profound effects. In the absence of exogenous ethylene, branches placed in 90% humidity had a fivefold increase in needle retention, 67% decrease in average water use, and had a final xylem pressure potential of –0.09 MPa. There was a near perfect relationship between VPD and needle retention (R2 = 0.99). These findings suggest that increasing xylem tension or decreasing water status may trigger ethylene synthesis and needle abscission. In addition, these findings demonstrate an effective means of controlling postharvest needle abscission by modifying temperature and/or relative humidity.

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Three experiments were conducted in greenhouses 1) to determine the optimal leaf-to-fruit ratio for minimizing the incidence of russeting (miniature cuticle cracks on fruit) while optimizing fruit yield of greenhouse tomato (Lycopersicon esculentum Mill.) and 2) to investigate the effect of day/night relative humidity (RH) regimens on the development of russeting. Leaf-to-fruit ratio treatments (0.5–2.0) were achieved by varying the number of fruit (two to six fruit) per cluster and the number of leaves (two to four leaves) between clusters. In one experiment, plants were also subjected to either high day/low night or low day/high night RH regimens (low RH, 60% to 70%; high RH, 85% to 95%). Results showed that russeting of greenhouse tomato was mostly influenced by the number of fruit per cluster (total fruit load), and very little by the number of leaves between clusters. In general, decreasing the number of fruit per cluster resulted in a progressive increase in the occurrence of russeting. Furthermore, as the number of fruit per cluster decreased, the percentage of fruit with no russeting and with little russeting decreased whereas the percentage of fruit with the more severe russeting increased (except for the summer). For beefsteak cultivars Trust and Rapsodie grown under southwestern Ontario conditions, the best pruning practices for minimizing russeting and optimizing yield was to prune clusters to three fruit in early spring and late fall, to four fruit during spring and fall, and to five fruit during the summer, with three leaves between clusters all year long. In the current study, no significant effect of day/night RH regimens on fruit russeting was observed. Of the cultivars used, Rz 74/56 was less sensitive to russeting than ‘Trust’, whereas ‘Rapsodie’ was not different from the two other cultivars. However, all three cultivars had a very high incidence of russeting (>65% of fruit affected), and none should be regarded as russeting resistant. Breeding programs and genetic investigations with the objective of developing greenhouse tomato cultivars resistant to russeting are needed.

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Most works on artificial lighting of winter greenhouse vegetable crops studied the effects of photosynthetic photon flux but rarely photoperiod. Over the last three years, we conducted experiments to find out the best photoperiods for production of greenhouse tomato and pepper. We found that extending photoperiod up to 20 hrs increased productivity of pepper plants while continuous light (24 hrs) decreased yields. For tomato plants, productivity reached a maximum under a 14-hr photoperiod while longer photoperiods (16 to 24 hrs) did not increase yields. For both pepper and tomato plants, optimal growth (shoot fresh and dry weights) was obtained under the same photoperiods that gave the best productivities. We also observed leaf chloroses on tomato plants after 6 weeks under photoperiods of 20 and 24 hrs and leaf deformations (wrinkles) on pepper plants exposed to continuous lighting. We also observed that plants under continuous light grew better and flowered earlier during the first 5 to 7 weeks of treatments. So, tomato and pepper plants can use advantageously continuous supplemental lighting for a short period of time but are negatively affected on a long term basis. Future works should look at varying photoperiods to optimize yields.

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Needle loss after harvest is a major problem for Atlantic Canada's Christmas tree and greenery industry. Ethylene is a signal for abscission in balsam fir, but preliminary studies have suggested that the role of ethylene may be influenced by length of exposure. Short-term and long-term ethylene exposure experiments were conducted. Branches were exposed to ethylene for 24 h (short-term) or continuously (long-term) at concentrations of 0 to 1000 ppm. The response variables measured were needle retention duration (NRD), average water use (AWU), and xylem pressure potential (XPP). Short-term exposure to any concentration of ethylene delayed needle abscission by 30 to 40 days. In contrast, long-term exposure to all concentrations of ethylene accelerated abscission, most evident by a 21-day decrease in NRD at 1000 ppm ethylene. There was a 60% decrease in NRD, 160% decrease (more negative) in XPP, and 80% increase in AWU as a result of long-term exposure to ethylene. Overall, our results demonstrate an opposite effect of short-term and long-term ethylene exposure, which suggests that short-term exposure to ethylene might help to precondition balsam fir and delay needle abscission during postharvest handling.

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Organic fertilizer regimens consisting of combinations of composts (yard waste, swine manure, or spent mushroom substrate) and liquid fertilizers (fish- or plant-based) were evaluated against conventional hydroponic fertilizers in two experiments with greenhouse tomatoes grown in peat-based substrate. Crop yield and fruit quality were evaluated and several assays of substrate microbial activity and community profiles (fluorescein diacetate analysis and EcoLog, values, nematode counts) were conducted. Crops grown in 20% to 40% compost (yard waste or yard waste plus swine manure) plus a continuously applied liquid source of organic potassium (K), calcium (Ca), magnesium (Mg), and sulphate (SO4) could not be sustained more than 1 month before nutrient deficiencies became visible. Supplementation with a nitrogen (N)- and phosphorus (P)-containing plant-based liquid fertilizer at the point when plant deficiencies became apparent subsequently produced yields ≈80% that of the hydroponic control. In a second experiment, the proportion of mushroom or yard waste compost was increased to 50% of the mix, and liquid delivery of K, Ca, Mg and SO4 plus either plant-based or fish-based N- and P-containing liquid feeds was started at the date of transplanting. In this case, organic yields equal to that of the hydroponic control (8.5 kg/plant) were observed in some treatments. The most productive organic treatment was the mushroom compost supplemented with a low concentration of the plant-based liquid fertilizer. In general, organic tomatoes had a lower postharvest decay index (better shelf life) than did the hydroponic controls, possibly as an indirect consequence of overall reduced yield in those treatments. High concentrations of both organic liquid feeds resulted in lower yields as a result of treatment-induced fusarium crown and root rot. In contrast to some previous studies, those treatments showing fusarium crown and root rot also had the highest gross microbial activity. Measures of gross microbial activity and numbers of microbivorous nematodes were higher (average of 37% and 6.7 times, respectively) in compost/organic feed treatments than in the hydroponic control. Community physiological profiles of the bacterial populations, on the other hand, did not differ between organic and hydroponic treatments. Nematode populations were significantly correlated with gross microbial activity in the organic treatments.

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