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Gagnon André Yelle Serge

In the summer of 1992, a 4-year research program on the utilisation of propane in agriculture was initiated between ICG Propane and Lava1 University. Experiments were conducted to evaluate the effects of propane burners on weed control as a pre-establishment treatment. The data indicate that the efficiency of weed control is related to tractor speed and gas pressure. When weed height is between 1 and 2 centimetres, most of the heat treatments were as effective as those with the herbicide paraquat. The best and most economical heat treatment was at a tractor speed of 6 Km-hr and a gas pressure of 65 PSI. With larger weeds, efficiency increased with reduces tractor speed and increased gas pressure. In addition, high intensity treatments provided excellent control on broadleaf weeds but were less efficient on grass species. A preliminary economical evaluation showed that propane burners are competitive with chemical herbicides and large-scale commercial trials are planned for summer 1994.

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Van Quy Le, Serge Overney, Binh Nguyen Quoc, and Serge Yelle

Tomato is one of the most important crop species where the introduction of foreign genes is expected to have a major impact on agriculture. Several transformation methods exist that rely on the cocultivation of various tissue or organ explants. However, tomato is still considered more difficult to transform than species such as Petunia hybrida and Nicotiana tabacum and can show widely varying success rates. Using cotyledonous explants, we propose a highly efficient procedure of Agrobacterium-mediated transformation and regeneration of an agricultural cultivated tomato (L. esculentum cv. Summerset). Results showed that up to 90% of the cotyledons generated callus within 3 weeks (1 to 5 calli/cotyledon) and 50% of them regenerated shoots in another 3 weeks. Finally, it resulted in 50 to 100 independent transgenic plants per 100 inoculated explants within 10 weeks. These results are at least 40% more efficient than those of already published protocols. Moreover, up to 95% of the regenerated plants that form vigorous de novo roots under the antibiotic selection tested positive for the GUS assay. Screening by PCR for the presence of the T-DNA genes gave the predicted DNA fragment bands. This high efficiency procedure was mainly achieved by 1) an adequate optimization of the hormone composition and concentration of the successive culture media; 2) the fresh explant wounding before the Agrobacterium infection (important for optimal cell transformations); 3) the explant position, inside down for callus induction and coculture period, and upside down for the selection and organogenesis period (important for antibiotic selection).

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Dominique Michaud, Serge Overney, Binh Nguyen-Quoc, and Serge Yelle

In the past few years, transformation of plant genomes with proteinase inhibitor (PI) genes has been proposed as an effective way to produce insect-tolerant plants. For such a control approach, however, biochemical studies are necessary to assess the effect of PIs on not only insect digestive proteinases (target enzymes) but also plant endogenous proteinases (nontarget enzymes). As an example, transformation of potato (Solanum tuberosum L.) with oryzacystatin (OC) genes, two cysteine PIs, was considered for controlling Colorado potato beetle (CPB; Leptinotarsa decemlineata Say). The use of electrophoretic approaches and standard assays showed that CPB uses at least 14 cysteine proteinases for protein digestion throughout its development. Proteinases of the same class were also detected in sprouting potato tuber extracts, suggesting a potential interference of cPIs in transgenic plants. While OCs inhibit a significant fraction of CPB digestive proteinases, no inactivation of potato proteinases was detected. This apparent absence of direct interference suggests the real potential of OCs for producing CPB-tolerant transgenic potato plants.

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Serge Overney, Dominique Michaud, Binh Nguyen-Quoc, and Serge Yelle

In recent years, several studies have demonstrated the potential of proteinase inhibitors (PIs) for controlling insect pests. Used as a component of an integrated pest management program, such an approach must, however, be considered with care, given the potential risks of interference on other control approaches. In particular, the effect of PIs on digestive proteinases of beneficial insects must be determined. As an example, this study analyzed the effect of oryzacystatins (OCs), two cysteine PIs isolated from rice, on digestive proteinases of Perillus bioculatus, a predator of the Colorado potato beetle (CPB; Leptinotarsa decemlineata Say), a major pest. Electrophoretic analyses showed the existence of several cysteine proteinase forms in the digestive tract of P. bioculatus. For each developmental stage, OCs dramatically inhibited proteolytic activity, showing an affinity between these inhibitors and the digestive proteinases of the predator. Despite their potential for controlling CPB, the two rice cystatins thus represent possible growth-suppressing compounds for the beneficial insect P. bioculatus. Work is currently under way to assess the compatibility of the two control approaches.

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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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Dominique-André Demers, Sylvain Dubé, Serge Yelle, and André Gosselin

Growing tomato and pepper plants under continuous light causes negative effects such as leaf chlorosis and deformities, and decreased growth and yield. Such effects are more pronounced on tomato plants. Our general objectives are to identify the physiological process(es) responsible for these negative effects and to explain the difference in sensitivity of tomato and pepper plants to continuous light. The specific objective of this experiment was to determine the effects of continuous light and light spectral composition on photosynthesis and related processes of tomato and pepper plants. Tomato and pepper plants were place on 7 June 1994 in growth chambers under photoperiod treatments of 12 h [high-pressure sodium (HPS) lamps], 24 h (HPS lamps), and 24 h [metal halide (MH) lamps]. For all treatments, FPP was 350 μmol·m–2·s–1, temperatures were 21C (day) and 17C (night), and RH was 70%. Every 2 weeks (7 June until 2 Aug.), tomato and pepper leaf samples were harvested and frozen in liquid nitrogen for subsequent measurements of starch content (Robinson et al, 1988, Plant Physiol.), sucrose phosphate synthase activities (Dali et al., 1992, Plant Physiol.) and chlorophyll and carotenoid content (determination on HPLC). A system that measured gas exchange and chlorophyll fluorescence of fresh leaf samples was used to determine the photosynthetic rate and quantum yield of CO2 fixation and electron transport. Development of the negative effects of continuous light on plants was monitored. Light spectral composition of the two types of lamps was measured using a spectroradiometer. Results show that, under continuous light, pepper plants were less-efficient than tomato plants in using light for CO2 fixation, but were more efficient in dissipating the extra energy received. This may explain why pepper plants are less sensitive to continuous light than tomato plants. MH lamps caused more-severe chloroses on tomato leaves than HPS plants. We believe that the higher proportion of UV-light provided by MH lamps may be related to this effect. Detailed results will be presented.

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Xiao-Fang Huang, Binh Nguyen-Quoc, and Serge Yelle

Sucrose synthase (SS) is one of the key enzymes in plant carbohydrate metabolism. In maize, this enzyme is encoded by two genes, Sh1 and Sus1. We have isolated and determined the 5'-upstream sequence of maize Sus1 gene and compared it with the corresponding sequence in Sh1 gene. Sequence analysis revealed that there was a weak homology between the two promoters and no common sequence elements were found. To understand the differential regulation of the expression of the two genes, we constructed chimeric GUS fusions using the two promoters of SS genes. By using the biolistic system, we delivered these constructs into various plant tissues, and their transient expression was studied. Our results showed that the two promoters of SS genes directed tissue-specific expression in the same way that the two genes are expressed in vivo. The effectiveness of the expression of the constructs was recorded by counting the total blue expression units (blue spots) per shot and by fluorometric assays. High levels of GUS activity were detected in the immature embryos, young coleoptiles, and heterotrophic young leaves bombarded with the Sus–GUS construct. More than 100 expression units were observed in these tissues. Compared with the transient expression of the 35S promoter in the same tissue, Sus promoter activity was twice as high. Strong Sus–GUS expression was also detected in the aleurone cells of developing kernels. In contrast, the Sh-GUS construct was expressed only in the endosperm with an activity twice as high as that of Sus–GUS and 35S–GUS in the same tissue. The results will be discussed in terms of the physiological roles of the two SS isozymes in plant tissues.

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Chantal J. Beauchamp, Yves Desjardins, Serge Yelle, and André Gosselin

Canadian environmental policies are aimed at reducing by 50%. the quantities of refuses intended for landfill by year 2000. In this perspective, landspreading and composting biosolids have been investigated as solutions. Paper sludges, wood wastes, and municipal solid wastes (MSW) are important components of landfill biosolids, but they are attractive by-products for agricultural use. Research projects were initiated to characterize the paper sludges produced by Daishowa Co. in Quebec City, wood wastes produced by Hydro-Quebec, and MSW composts produced from waste treatment at RITDM (Chertsey) and Conporec (Sorel). De-inked paper sludge and wood wastes have been landspreaded for growing potato and landscaping, whereas composted paper sludges have been evaluated as part of potting media for growing greenhouse plants and landspreaded for turfgrass production. The chemical and biological characteristics of these biosolids were investigated for their fertilization potential and their effect on plant growth.

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Henriette Gotoèchan, Jean Coulombe, Serge Yelle, and Hèlène Desilets

Two cultivars of carrot were sown in a sandy loam soil over two seasons with and without introduction of commercial inoculum of Glomus intraradices or Glomus etunicatum, which was spread with an experimental sowing machine. VAM fungi effects on the yield and the quality of carrot varied from season to season. In 1997, both of the VAM fungi enhanced the average saleable yield of the two cultivars from 66.21 t/ha to 69.85 t/ha and 80.81 t/ha, respectively, for the treatment without the introduction of VAM fungi, G. etunicatum, and G. intraradices. The slight difference (5.03%) that occured between G. intraradices and the non-inoculated treatment, although not significant, represented 20.38% of the total percentage of rejected carrots. For the last season, the amount of rejected carrots was in the same range for all the treatments (13% to 14%). Nevertheless, both of the cultivars responded differently to mycorrhization. In both of the seasons, mycorrhizal colonization was high in all plots, with an average of 70% in the treatment without inoculation and 75% in those that received G. intraradices or G. etunicatum. In our experimental conditions, reduction of phosphate fertilization to 50% of the recommanded quantity had no influence either on the mycorrhizal colonization or on the yields.

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Han-Ling Yu, Claude Willemot, Serge Yelle, Yves Castonguay, and Paul Nadeau

Translatable mRNAs from two tomato (Lycopersicon esculentum Mill.) cultivars differing in chilling tolerance were compared after 16 days of chilling at 4C and after return to 20C for 1 and 5 days. Before chilling, the translation products, resolved by 2D NEPHGE, showed significant differences between more tolerant `New York 280' (NY) and less tolerant `Early Cherry' (EC). In NY, chilling reduced the level of five to 10 mRNAs and enhanced or induced that of several other mRNAs. After transfer to 20C, the trend was progressively reversed. Changes in the levels of two low-molecular-weight basic peptides were most noticeable. One, absent in NY before chilling, was strongly expressed after chilling and 24 h after transfer to 20C, but disappeared 5 days after transfer. The level of this peptide increased slightly in EC at low temperature and was maintained after transfer to 20C. The level of the other, high in NY before chilling, was sharply reduced after chilling. In contrast, the level of this polypeptide was low in EC under all treatments.