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Y. Desjardins and J. Abdulnour

Microtubers (Solanum tuberosum cv Snowden) were produced in 1-L jar fermentors using a two-step method consisting of a shoot multiplication phase (21 days) followed by a tuberization phase (25 days). The plantlets were immersed in Murashige and Skoog (MS) liquid medium for 3.5 min every 4 h. Low concentrations of ancymidol (anti-gibberellic substance), particularly during the shoot multiplication phase, were essential for tuber initiation and development. A continuous supply of 2 μMol ancymidol during the two phases of culture decreased plant height, but produced >100 microtubers per jar. Although the tuber development phase was short (25 d), 25% of the microtubers produced were >0.5 g with 17.5% to 18.0% of dry-matter content.

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S. Aquin, Y. Desjardins, and L.-P. Vézina

A study was conducted to determine the implication of nitrate reductase (NR) and glutamine synthetase (GS) during the transition of micropropagated plantlets from heterotrophy to photoautotrophy to document how nitrogen metabolism interfaces with photosynthetic and anaplerotic CO2 fixation. The activity of the two enzymes was determined in different tissues at different organogenic stages during the development of plantlets transferred onto rooting media containing varying quantities of sucrose. Under 3% sucrose, NR activity was much higher in leaves than in crown tissues. When roots are initiating, there is a shift in the proportion of nitrate reduction from leaves to crown. As roots mature, the proportion of nitrate reduction increases in roots. Similar trends were observed under 5% sucrose. In contrast, under 1% sucrose, a higher proportion of the nitrate is reduced in the leaf tissues throughout the culture period. This suggests that nitrate is reduced mainly in leaves in photoautotrophic plantlets, while it is reduced in crowns and root tissues for mixotrophic plantlets. In general, the GS activity follows the pattern of NR, but is always in excess, to enable rapid assimilation of ammonium derived from metabolism and medium absorption.

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P. Lecomte, M. Laganière, and Y. Desjardins

Increasing costs associated with the disposal of industrial and urban wastes necessitate the development of alternatives which are economical and environmentally safe. With >3000 ha in Quebec, sod production represents an interesting alternative for the use of new amendments, such as composted de-inked paper sludges and municipal waste compost. The objective of this trial was to evaluate the potential benefits of these amendments (nutrient retention in the root zone and chemical and physical soil benefits) and question potential environmental hazards. Chemical dynamics of N, P, K, micronutrients and heavy metals were examined over four soil layers (0 to 15, 15 to 30, 30 to 60, an >60 cm) on sandy and clay soil. Preliminary results for 1993 and 1994 indicate that nutrient concentrations in water extract are high following the establishment of sites. When sod is absent, high concentrations of lead (500 mg·kg–1 in urban compost) show only a slight trend to accumulate. Nevertheless, this new approach toward using industrial and urban composts seems to be adequate and economically attractive.

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M. Laganière, P. Lecomte, and Y. Desjardins

In Quebec, commercial sod is produced on >3000 ha. Generally, ≈20 months are required to produce market-ready sod. When conditions are suitable, harvest of marketable sod is possible within a year. However, intensive management may result in soil compaction and a reduction of the organic matter content. Considering the increasing amount of amendment available, sod production fields could be interesting for their disposal. In this study, visual quality and sod root growth was examined following an application of an organic amendment at 50, 100, and 150 t·ha–1, incorporated to depth of 6 or 20 cm. Plots established on a sandy soil receiving organic amendments had higher visual quality ratings. Bulk density was significantly reduced following compost or paper sludge application to a heavy soil. The shearing strength required to tear sod amended with compost was significantly higher in comparison with control and paper sludge treatments.

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J. Dionne, M. Laganière, and Y. Desjardins

Extensive winterkill of golf greens is a major problem in northern climates. In this study, the efficiency of several protective covering materials used to shelter Poa annua golf greens from winter damages was evaluated over 2 years. The bioclimatological environment under these protective covers was studied at crown level and at 5, 10, and 20 cm under the ground Treatments (permeable and impermeable covers, curled wood Excelsior mat, straw mulch protected by an impermeable cover, geotextile material with an impermeable cover, and air space under an impermeable cover) were compared to a control treatment without protection. Results indicate that temperature profile was strongly influenced by both winter protection covers and snow depth Temperatures at crown level were stable and just below 0C under plots covered with a significant amount of snow. However, temperatures varied considerably, when snow cover was <15 cm. Snow thermal conductivity was increased by periods of rain during the winter. Impermeable covers minimized the negative effect of this change in the insulation properties of the snow cover by limiting temperature fluctuations at the crown level. Temperature profiles under permeable covers were similar to profiles observed on control plots. Temperature profiles were comparable for 5 and 10 cm air space treatments and were not significantly different when compared to impermeable covers spread directly on the turf. Straw with an impermeable cover and Excelsior mats maintained crown level temperatures at >0C and the incidence of disease was higher under these highly insulative materials.

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F. Chéour, C. Willemot, J. Arul, J. Makhlouf, and Y. Desjardins

The objective of this study was to compare the effects of the foliar application of CaCl2 on the shelf life and Ca content of the fruit of the strawberry (Fragaria × ananassa) cultivars Kent and Glooscap, which differ in fruit firmness. Calcium was applied repeatedly, 3 days, 3 and 6 days, or 3, 6, and 9 days before harvest at 0, 10, or 20 kg·ha-1. Calcium treatment influenced amounts of free sugars and organic acids, color, texture, and disease development during storage in air at 4C. Calcium application had more effect on the fruit of the softer `Glooscap', which contained relatively low levels of Ca at the time of treatment. Calcium content of the fruit appeared to depend mainly on the ability of the plant to accumulate and distribute Ca.

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H. Wang, S. Parent, A. Gosselin, and Y. Desjardins

Micropropagated plantlets of Gerbera jamesonii H. Bolus ex Hook. F. `Terra Mix', Nephrolepis exaltata (L.) Schott `Florida Ruffles', and Syngonium podophyllum Schott `White Butterfly' were inoculated with two vesicular-arbuscular mycorrhizal (VAM) fungi, Glomus intraradices Schenck and Smith and G. vesiculiferum Gerderman and Trappe. They were potted in three peat-based media to determine the effects of mycorrhizal peat substrate on acclimatization and subsequent growth of micropropagated plantlets under greenhouse conditions. Symbiosis was established between the three ornamental species and VAM fungi within 4 to 8 weeks of culture in the greenhouse, but not during acclimatization. Mortality of Gerbera and Nephrolepis mycorrhizal plantlets was reduced at week 8 compared to the noninoculated control. A peat-based substrate low in P and with good aeration improved VAM fungi spread and efficiency. Mycorrhizal substrates had a long-term benefit of increasing leaf and root dry weight of Gerbera and Nephrolepis. Mycorrhizal Gerbera plants flowered significantly faster than non-mycorrhizal plants.

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L. Chercuitte, J.A. SulIivan, Y.D. Desjardins, and R. Bedard

The waiting-bed (WB) system has the potential to significantly increase the length of the strawberry (Fragaria Xananassa Duch.) production season. In the WB phase of this system the plants were deblossomed and runners were removed to stimulate the production of a multiple crowned plant. The objective of this study was to examine the influence of planting date and cultivar on yield potential and vegetative growth of the strawberry plants in the WB and cropping beds (CB). Experiments were conducted in Ontario and Quebec. Early establishment of the WB favored the production of large multicrown plants. `Kent' appeared to be the best cultivar among five tested due to the many berries produced because of good fruit set. Yield potential was not realized in late-planted CB. The highest yields per plant (273 g) were obtained in Quebec with plants from the earliest WB. Yields in CB decreased with later plantings due to stress of transplanting when air and soil temperatures were high. Berry count was identified as the yield component most affected by the later planting date of the CB. The WB system has potential for season extension in strawberry, but WB must be established early in the season to encourage the development of a plant with high yield potential.

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F. Chéour, C. Willemot, J. Arul, Y. Desjardins, J. Makhlouf, P.M. Charest, and A. Gosselin

Effects of CaCl2 preharvest treatment on postharvest strawberry (Fragaria × ananassa) ripening and gray mold development were assessed. Two experiments were carried out in 1987 on two sites. In the first experiment, the effects of rate of application of CaCl2 and degree of fruit maturity at treatment were studied with the conventional cultivar Kent. In the second experiment, the influence of concentration and frequency of application of CaCl2 was investigated with day-neutral `Tribute'. Calcium treatment caused a significant increase in fruit and leaf Ca contents, which were closely correlated. The degree of fruit maturity at application and the frequency of treatment did not affect Ca concentration in the tissues. Several maturity criteria were measured during fruit storage in air at 4C. Anthocyanin and free-sugar contents and tissue electrical conductivity increased, while titratable acidity and firmness decreased. In both experiments, Ca treatment delayed ripening and gray mold development. The delay increased with increasing Ca concentration.