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.
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.
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.
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.
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.
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.
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.
Hassan Zekki, André Gosselin, and Laurent Gauthier
In greenhouses, computerized climate control systems can be used to dynamically and automatically regulate climatic and environmental parameters. To support such a mode of operation, a crop growth model that was developed for greenhouse tomato plants (TOMGRO) was chosen. The model describes the phenological development and increase in dry weight of various organs from planting till maturity under variable environmental conditions. The assimilate partitioning is based on sink strength. A FORTRAN version of TOMGRO was converted to the Smalltalk object-oriented programming environment. This model was integrated into GX, a dynamic climate management software system that was developed at Laval Univ. GX defines a general architecture that may accommodate different decision-making modules based on mathematical models and rule bases. The TOMGRO model is being used to evaluate different production scenarios and will be used to calculate and predict crop growth rates, development, and yields. The model can be used to perform real-time and seasonal cost–benefit analysis and for the dynamic optimization of greenhouse climatic parameters.
Hui-lian Xu, Laurent Gauthier, and André Gosselin
Tomato plants were grown in peatmoss-based substrate and supplied with nutrient solution of high (4.5 mS·cm–1) or low (2.3 mS·cm–1) electrical conductivity (EC) under high (95%) or low (55% of capillary capacity) substrate water content (SWC) to examine the effects of high EC and low SWC on growth and physiology. Salts were allowed to accumulate in the substrate for 7 weeks. Both high EC and low SWC significantly decreased dry matter production (DMP) and fruit yield (FY). Fruit harvest index was lower in high EC- or low SWC-treated plants. Decrease in marketable FY was attributed to both the decrease in total FY and the increase in small and abnormal (cracked and rot) fruits. Both high EC and low SWC decreased photosynthesis (PN) and leaf water potential (ΨL). However, chlorophyll content and respiration were increased by high EC under both high and low SWC. Water consumption based on both whole plant and unit of leaf area was decreased by high EC and low SWC. ΨL and transpiration were depressed by high EC and low SWC, especially at midday. There was a significant positive correlation between fruit yield and water consumption. The effects of high EC and low SWC were additive on most of the variables. Decreases in ΨL might ultimately account for water consumption reduction, PN depression, and FY decrease.