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  • Author or Editor: Andre Gosselin x
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The CRH consists of 20 professors and researchers as well as more than 50 graduate students enrolled at the master or doctorate level in the various departments of the Faculty of Agriculture and Food. The scientific program of the CRH is articulated around the theme of quality and availability of Quebec horticultural products. This multi-disciplinary program comprises: production systems, plant pathology, in vitro culture and somatic hybridization, bio-climatology, and engineering of these processes as well as post-harvest technology and marketing of horticultural products. Our goals are evidently to improve production systems but they are also aimed at the quality and innocuity of horticultural products as well as using environment-friendly technologies.

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Strawberry plantlets (Fragaria X ananassa Duch. cv. Kent) were submitted to a factorial arrangement of 2 photosynthetic photon fluxes (PPF) (80 and 150 μmol·m-2·s-1, PAR) and 2 CO2 concentrations (330 and 3000 ppm) during the in vitro rooting stage. Leaves were tagged and placed in a growth chamber tor acclimatization. Photosynthetic capability of leaves from different origins was determined by measuring the initial and total activity of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (rubisco), but the contribution of Phosphoenolpyruvate carboxylase (PEPCase) to fixation was also examined High CO2 concentration and PPF significantly increased fresh weight and surface area in vitro and after 4 weeks ex vitro. Improved growth was not the result of increased autotrophy in vitro since initial rubisco activity was 10 times lower than that of de novo formed leaves and declined under high CO2 and PPF. Carbon dioxide concentration and PPF had no effect on total activity of rubisco. Low activation state and total activity of rubisco in in vitro leaves is the cause of poor photosynthetic activity in vitro Persistent in vitro leaves after 4 weeks of acclimatization did not have higher total activity of rubisco, but the activation state was 4 times larger than the corresponding activity in vitro which might thus provide for non-negligible contribution to photosynthetic carbon assimilation. The possible inhibition of photosynthesis by the presence of sugar in the medium is discussed.

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Tomato plants were submitted to three photosynthetic photon fluxes (PPF) of 50, 100, and 150 μmol. m-2s-1 and cluster-pruned according to different scenarios. The highest PPF combined with severe cluster pruning produced the highest yield and the best fruit quality. The highest PPF increased growth, photosynthesis and leaf sugar content. Severe cluster pruning increased the average fruit weight, leaf sucrose and glucose content, but reduced photosynthesis. Data will be discussed in relation to crop management and efficiency.

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Since they grow nearly exponentially, plants in their juvenile phase can benefit more than mature ones of optimal growing conditions. Transplant production in greenhouses offers the opportunity to optimize growing factors in order to reduce production time and improve transplant quality. Carbon dioxide and light are the two driving forces of photosynthesis. Carbon dioxide concentration can be enriched in the greenhouse atmosphere, leading to heavier transplants with thicker leaves and reduced transpiration rates. Supplementary lighting is often considered as more effective than CO2 enrichment for transplant production. It can be used not only to speed up growth and produce higher quality plants, but also to help in production planning. However, residual effects on transplant field yield of CO2 enrichment or supplementary lighting are absent or, at the best, inconsistent.

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Exposure of tomato and pepper plants to long photoperiods (20 hours or more for tomato; 24 hours for pepper) results in leaf chlorosis (tomato), leaf deformities (pepper), and decreased growth and productivity (both species). Some researchers have suggested that excessive starch accumulation in the leaves could be the cause of the negative effects. We observed that tomato and pepper plants do accumulate more starch in their leaves when grown under a long photoperiod (24 hours) compared to a shorter one (16 hours). However, our results indicated that these accumulations were not caused by a limited sink strength but by an alteration of the carbon metabolism at the leaf level. In our last experiment, we studied the activity of enzymes [sucrose phosphate synthase (SPS), sucrose synthase (SS), invertase] of leaf carbon metabolism in tomato and pepper plants grown under different photoperiods (natural, natural + supplemental light of 100 μmol·m-2·s-1 during 16 and 24 hours). We observed a 10% to 15% decrease in leaf SPS activity in tomato (not in pepper) plants grown under a 24-hour photoperiod. In both species, invertase and SS activities were not affected by photoperiod treatments. In tomato plants grown under a 24-hour photoperiod, the decrease in SPS activity corresponded to the appearance of leaf chlorosis (6 to 7 weeks after the beginning of treatments). Therefore, it appears that leaf carbon metabolism could be involved in the development of negative effects of long photoperiod in tomato plants, but not in pepper plants. The fact that photoperiod had no apparent effect on leaf carbon metabolism of pepper may explain why this species can tolerate longer photoperiods than tomato plants.

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Six fertilization programs were applied to three woody plants: Physocarpus opulifolius `Nanus', Spiraea × bumalda `Gold flame', and Weigela florida `Rumba'. The objective of this study was to determine fertilization programs best adapted to container woodyplant production. Treatments were: 1) Nutricote (5 g/liter of growth medium) + weekly fertigation of 20N–20P–20K (300 mg N/liter); 2) Coïc-LeSaint solution for each irrigation; 3) Nutricote + weekly fertigation of liquid 9N-9P–9K (300 mg N/liter); 4) fertigation with complete nutrient solution (125 mg N/liter); 5) Polyon + weekly fertigation of 20N–20P–20K (300 mg N/liter); and 6) Nutralene + weekly fertigation of 20N–20P–20K (300 mg N/liter). The experiment took place between 25 June 1991 and 15 Aug. 1992. Results show that, independent of species, plants given fertilization program 4 had lower plant height (57 cm) and stem dry weight (97 g) than plants under other treatments, the average for each parameter being 72 cm and 127 g, respectively. Plant height was highest in Physocarpus with treatment programs 2, 4, 5, and 6. Weigela had greater growth under program 2, while Spiraea had more growth with programs 1, 3, and 6. Consequently, differences exist between optimum fertilization programs used for each species studied.

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Abstract

Celery seedlings (Apium graveolens L. cv. Florida 683) were seeded in multicell styrofoam trays containing a commercial peat mix. They were irrigated with nutrient solutions containing three N fertilizations (150, 250, or 350 mg N/liter) and three NO3:NH4 ratios (1:1, 2:1, or 3:1) in factorial combinations. Growth measurements and saturated medium extracts were obtained on days 38, 45, and 52 after seeding. Increasing N fertilization increased leaf area and shoot dry weight, but decreased root dry weight and root : shoot ratio. The lowest NO3:NH4 ratio had increased the percentage of shoot dry matter by the end of the experiment. Nitrogen was preferentially taken up as NH4-N. The composition of the fertilizer solution had a greater effect on young celery seedlings than on older ones. A minimum of 250 mg N/Iiter at a NO3:NH4 ratio of 2:1 appears to be adequate for celery seedlings grown in multicells.

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Abstract

Celery seedlings (Apium graveolens L. cv. Florida 683) were seeded in multicell styrofoam trays containing a commercial peat mix. They were fertilized with nutrient solutions at two nitrogen fertilizations (150 or 350 mg N/liter), two NO3:NH4 ratios (2:1 or 3:1), and two urea-N levels (0% or 50%) in factorial combinations to determine main and interactive effects of urea on seedling growth, nutrient status, and crop yield. Urea used in combination with low N improved the percentage of shoot dry matter and increased leaf area, shoot and root dry weight, and root: shoot ratio of the seedlings. Urea proved beneficial in improving transplant yield potential under high-N fertilization.

Open Access

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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