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Nicolas Tremblay and André Gosselin

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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Blanche Dansereau and André Gosselin

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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Jeffrey Norrie and André Gosselin

Waste residues arising from paper production, either from recycled (deinking) or virgin wood (primary) fibers, are composed primarily of lignin, cellulose and hemi-cellulose. Large quantities of such residues are usually landfilled or burned. In a joint project with the company “Les Composts du Quebec Inc.',” this study examined the use of deinking and primary paper sludges as partial constituents of substrate mixtures, used as organic soil amendments for the growth of several grass and tree species. In a strip-split-plot design, mixtures of paper sludge (0% to 50%), sand (50%) and organic soil (0% to 50%) were prepared with or without a base-fertilization (strip-plot) before planting. Base fertilizations were given to improve N, P, and K availability and C/N and C/P ratios based on the nutrient status of substrate mixtures before incorporation into the soil. Results over both years indicated that unfertilized treatments with a higher percentage of paper sludge (by dry volume) generally displayed poorer growth. Grass plots exhibited decreased ground cover and stand quality. Shrubs showed some deficiency symptoms, but not until late in the season of each year. However, few differences were found between sludge treatments for grass or shrub species if substrates were given a base-fertilization of N, P, and K (to 0.5%, 0.13%, and 0.33%, respectively). Again, during the 2nd year, few differences were found between sludge-amended plots that were base-fertilized the year before. In short, our results indicate that paper sludge amendments can maintain or improve the growth of grass and shrub species if an adequate base fertilization is given to overcome nutrient immobilization. Several, more-precise base-fertilizer treatments are currently being examined for turfgrass culture.

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Yves Desjardins and André Gosselin

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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Mohammed Dafiri and André Gosselin

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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Dominique-André Demers, Serge Yelle and André Gosselin

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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Isabelle Duchesne, Jacques-André Rioux and André Gosselin

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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Yves Desjardins, André Gosselin and Michel Lamarre

Asparagus (Asparagus officinalis L.) transplants and in vitro-cultured clones were grown and acclimatized under two photosynthetic photon flux (PPF) conditions (ambient and ambient + 80 μmol·s-1·m-2) and three atmospheric CO2 concentrations (330, 900, and 1500 ppm). Short- and long-term effects were measured in the greenhouse and after two seasons of growth in the field, respectively. In the greenhouse, CO2 enrichment (CE) and supplemental lighting (SL) increased root and fern dry weight by 196% and 336%, respectively, for transplants and by 335% and 229%, respectively, for clones. For these characteristics, a significant interaction was observed between SL and CE with tissue-cultured plantlets. In the absence of SL, CE did not significantly increase root or shoot dry weight. No interaction was observed between CE and SL for transplants, although these factors significantly improved growth. It was possible to reduce the nursery period by as much as 3 weeks with CE and SL and still obtain a plant size comparable to that of the control at the end of the experiment. Long-term effects of SL were observed after two seasons of growth in the field. Supplemental lighting improved survival of transplants and was particularly beneficial to in vitro plants. Clones grown under SL were of similar size as transplants after 2 years in the field.

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Michel Carrier, André Gosselin and Laurent Gauthier

A dynamic management strategy for supplemental lighting in greenhouses was developed. It makes use of a plant growth model and of a rule-based decisionmaking protocol within the framework of a generic greenhouse climate management software system. The model, an adapted version of SUCROS87, tracks plant growth and predicts dry weight production based on measured or estimated values of light intensity, temperature, and CO2 concentration. A set of logical predicates (rules) implements the strategy's behavior. Optimization of lamp use was conducted as a function of economic criteria that enable a comparison between the additional income associated with yield increases due to supplemental lighting and incurred cost increases. Although the model is not perfectly reliable in its predictions, the system can be used to simulate the effect of changes to economic parameters on the decisions of the management strategy. The dynamic strategy described here differs from conventional supplemental lighting scenarios in the sense that it increases the length of the period of supplemental lighting when the daily solar light integral is low, and reduces or eliminates the use of supplemental lighting when the weather forecast predicts that the daily solar light integral will exceed plant requirements.