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  • Author or Editor: A. Gosselin x
  • Journal of the American Society for Horticultural Science x
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Tomato plants (Lycopersicon esculentum Mill. cv. Capello) were grown in the three most promising and used hydroponic cultivation systems using rockwool and peatmoss substrates and nutrient film technique (NFT), either with or without recovery and recycling of the drainage solutions. Prolonged recycling of nutrient solutions in NFT caused a reduction in fresh weight, dry weight, and yield compared to plants grown in NFT with regular renewal of the nutrient solution. There were no differences in growth, productivity, and leaf mineral composition between plants grown in rockwool and peatmoss systems, with or without recycling, and in the NFT system without recycling. These results suggest that recycling drainage solutions is an economically and environmentally sound horticultural practice that when used correctly does not cause a reduction in yield of tomatoes cultivated in rockwool or peatmoss. However, prolonged use of the same solution in the NFT cultivation system can negatively affect growth and yield. This is most likely due to an accumulation of sulfate ions in the fertigation solutions.

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Daily and seasonal variations of photosynthetic activity, chlorophyll a (Chl-a) fluorescence and foliar carbohydrate content were studied in situ on greenhouse tomato (Lycopersicon esculentum Mill. `Trust') plants grown under CO2 enrichment and supplemental lighting. The objective of this study was to assess the effect of seasonal variation of the photosynthetic photon flux (PPF) on photosynthetic efficiency of tomato plants and to determine the presence or absence of photosynthetic down-regulation under greenhouse growing conditions prevailing in northern latitudes. During winter, the fifth and the tenth leaves of tomato plants showed low, constant daily photosynthetic activity suggesting a source limitation under low PPF. In winter, the ratio of variable to maximum Chl-a fluorescence in dark adapted state (Fv/Fm) remained constant during the day indicating no photoinhibition occurred. In February, an increase in photosynthetic activity was followed by a decline during March, April, and May accompanied by an increase in sucrose and daily starch concentrations and constant but high hexose level. This accumulation was a long-term response to high PPF and CO2 enrichment which would be caused by a sink limitation. Thus, in spring we observed an in situ downregulation of photosynthesis. The ratio Fv/Fm decreased in spring compared to winter in response to increasing PPF. The daily decline of Fv/Fm was observed particularly as a midday depression followed by a recovery towards the end of the day. This indicated that tomato leaves were subject to a reversible inhibition in spring. Fv/Fm was lower in March than in April and May even though PPF was higher in April and May than in March. These results suggest that tomato plants develop an adaptive and protective strategy as PPF increases in spring.

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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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The use of potential evapotranspiration (PET) estimates to identify irrigation timing for greenhouse tomatoes (Lycopersicon esculentum Mill.) grown in peat-based substrate was evaluated for a spring and fall crop. PET (using the Penman equation) was calculated from leaf, wet and dry bulb temperatures, and incident and reflected photosynthetic photon flux. Substrate matric potential (SMP) was monitored continuously using electronic tensiometers. Two irrigation starting setpoints (-4.5 and -6.5 kPa SMP) and two nutrient solution electrical conductivity (EC) treatments (1.5 and 3.0 dS·m-1) were factorially combined in a completely randomized design. Irrigation frequency was greater in treatments irrigated at -4.5 than at -6.5 kPa. The integral of calculated PET values was correlated with SMP for both experiments. Accumulated PET values were higher at the start of irrigation in the -6.5-kPa treatments for spring and fall crops. Nutrient solution EC did not influence irrigation frequency. Leaf pressure potential (LPP) was correlated to PET-predicted LPP (r 2 > 0.56) in plants subjected to high EC, low (-6.5 kPa) matric potential setpoint, or both treatments. PET and electronic tensiometer technology can be used jointly to improve irrigation management for tomatoes grown in peat-based substrates by more accurately responding to crop needs for water and nutrients.

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Our objective was to determine the relationship between daily and seasonal changes in understory light, and growth of 1- and 2-year-old american ginseng plants cultivated in a broadleaf forest. Using hemispherical photography and spectroradiometry, understory light [total, direct, and diffuse photon flux density (PFD), and sunfleck durations] and light quality [ultraviolet (UV) and red to far red (R:FR)] were evaluated during two consecutive growing seasons. While shoot and root dry weight (DW), and taproot area of 1-year-old american ginseng plants were related to sunfleck durations, accounting for up to 56% of the variation, the relationship reached a plateau at 2 h·d-1 sunfleck durations for growth. In September, growth of 1- and 2-year-old plants exposed to <2 h·d-1 sunfleck durations was positively related to diffuse PFD (and total PFD for 1-year-old plants), accounting for up to 69% of the variation. In mid-season (July 2000), shoot and root growth, and leaflet area of 2-year-old american ginseng were correlated with light PFD and light quality (UV and R:FR), accounting for up to 88% of the variation. Generally, the results suggest that exposing 1- and 2-year-old american ginseng plants to higher diffuse PFD and <2 h·d-1 sunfleck durations increases yield.

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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.

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