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Stephanie Burnett, Paul Thomas, and Marc van Iersel

We previously found that incorporation of PEG-8000 into the growing medium delayed germination and resulted in shorter seedlings. However, in that study, we were unable to determine whether the reduced height was merely the effect of delayed germination or of reduced elongation after germination. To answer this question, we studied whether postgermination drenches with PEG-8000 can reduce seedling height. Annual salvia (Salvia splendens F. Sellow. ex Roem. & Shult. `Bonfire') and French marigold (Tagetes patula L. `Boy Orange') seedlings were treated with drenches of PEG-8000: 0, 15, 20, 30, 42, 50, 62, 72, or 83 g·L–1. At least 20% of seedlings treated with 62 to 83 g·L–1 of PEG-8000 were dead 14 d after treatment. Salvia and marigolds treated with the remaining PEG-8000 concentrations were up to 34% and 14% shorter than untreated seedlings, respectively. Leaf water (Ψw) and turgor potential (Ψp) also decreased for salvia which were grown with greater concentrations of PEG-8000, one probable cause of the observed reduction in elongation. Since the PEG-8000 in this study was applied after germination, it is clear that PEG-8000 does not reduce elongation merely by delaying germination, but also by reducing the elongation rate. Thus, postgermination drenches with PEG-8000 can be used to produce shorter seedlings.

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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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Shi-Ying Wang, William H. Carlson, and Royal D. Heins

The effect of 6 weeks of storage at 2.5, 5.0, 7.5, 10.0, or 12.5°C in a glass greenhouse was determined on 11 vegetatively propagated annual species. Fresh weight (total, shoot, and root) and height of 30 plants per species in each storage temperature were measured at the end of storage. Another 30 plants were transplanted into 15-cm pots (three plants per pot) and grown under natural light in a 20°C glass greenhouse for 3 weeks. Three species showed chilling injury or died during storage at ≤7.5°C. Plant height and shoot fresh weight at the end of storage for most species increased linearly as storage temperature increased. Storage temperature did not affect the net increase in height or weight significantly during recovery growth, except for plants that exhibited chilling injury at the end of storage.

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M.R. Evans and G. Li

The annual bedding plants `Dazzler Rose Star' impatiens (Impatiens wallerana), `Cooler Blush' vinca (Catharanthus roseus), `Orbit Cardinal' geranium (Pelargonium × hotorum), `Janie Bright Yellow' marigold (Tagetes patula) and `Bingo Azure' pansy (Viola tricolor) were grown on germination papers treated with deionized water (DI), 2500 or 5000 mg·L-1 (ppm) humic acid (HA) or nutrient control (NC) solutions. Seedlings grown on HA-treated germination papers had higher dry root weights than those grown on DI or NC-treated germination papers. Except for impatiens, seedlings germinated on HA-treated germination papers had higher lateral root numbers and higher total lateral root lengths than those grown on DI and NC-treated germination papers. Impatiens grown on NC-treated germination papers had higher lateral root numbers than those grown on DI or HA-treated germination papers. Overall, lateral root numbers for impatiens were higher for seedlings germinated on HA-treated papers than DI or NC-treated papers and highest lateral root numbers occurred on those impatiens germinated on papers treated with 5000 mg·L-1 HA. Except for geranium, seedlings grown in HA-amended sphagnum-peat-based substrates had similar dry root and dry shoot weights as those grown in unamended substrates. Geranium seedlings grown in HA-amended sphagnum peat-based substrates had significantly higher dry root weights than those grown in unamended substrates. However, dry shoot weights of geranium grown in HA-amended sphagnum peat-based substrates were similar to those grown in unamended substrates.

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A. Liptay and P. Sikkema

Tomato (Lycopersicon esculentum Mill) seedlings given 0.3 to 0.4 L/tray per day of a mineral solution containing (in mg·L-1) 150N-47P-216K-64Ca-40Mg maintained optimal height at 10 to 13 cm for Ontario processing tomato transplants. Seedlings given greater fertigation volumes were too tall and spindly to use as transplants. Transplants given 0.2 L of water per tray per day were very short (6 cm) compared to those receiving 0.3 to 0.4 L. As fertigation volume was increased from 0.2 to 0.7 L, shoot N remained constant while root N increased. Shoots had about a 3-fold higher level of N, P, and K than the roots. Calcium and magnesium were similar in roots and shoots. Mineral leaching from the trays was 1% of the total volume applied for the 0.4-L and 4% for the 0.7-L treatment.

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Sandra B. Wilson, Jeongwook Heo, Chieri Kubota, and Toyoki Kozai

Sweetpotato [Ipomoea batatas (L.) Lam., `Beniazuma'] plantlets were grown photoautotrophically (without sugar) for 12 days in an improved forced ventilation system designed with air distribution pipes for uniform spatial distributions of carbon dioxide (CO2) concentration. Enriched CO2 conditions and photosynthetic photon flux (PPF) were provided at 1500 μmol·mol-1 and 150 μmol·m-2·s-1, respectively. The forced (F) ventilation treatments were designated high (FH), medium (FM), and low (FL), corresponding to ventilation rates of 23 mL·s-1 (1.40 inch3/s), 17 mL·s-1 (1.04 inch3/s), and 10 mL·s-1 (0.61 inch3/s), respectively, on day 12. The natural (N) ventilation treatment was extremely low (NE) at 0.4 mL·s-1 (0.02 inch3/s), relative to the forced ventilation treatments. Total soluble sugar (TSS) and starch content were determined on day 12. Total soluble sugars (sucrose, glucose, fructose) of FH plantlets were lowest in leaf tissue and highest in stem tissue as compared to other ventilation treatments. Starch concentration was higher in leaf tissue of FH or FM plantlets as compared to that of FL or NE plantlets. Plantlets subjected to FH or FM treatments exhibited significantly higher net photosynthetic rates (NPR) than those of the other treatments; and on day 12, NPR was almost five times higher in the FH or FM treatment than the FL or NE treatments. Carbohydrate concentration of plantlets was also influenced by the position of the plantlets in the vessel. Within the forced ventilation vessels, leaf TSS of FH and FM plantlets was similar regardless of whether plantlets were located near the inlet or outlet of CO2 enriched air. However, under FH or FM conditions, leaf starch concentration was higher in plantlets located closest to the CO2 inlet as compared to the outlet.

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Bradley S. Sladek, Gerald M. Henry, and Dick L. Auld

artificial shade conditions. Materials and Methods Experiments were conducted in 2006 and 2007 at the Texas Tech University Horticulture Greenhouse in Lubbock, TX. Plugs measuring 2.5 cm 2 of six zoysiagrass genotypes [ Zoysia japonica Steud. genotype

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Kurt Steinke, David R. Chalmers, Richard H. White, Charles H. Fontanier, James C. Thomas, and Benjamin G. Wherley

osmotic regulation resulting in higher turgor pressures. The present study was conducted to evaluate the recuperative potential of transplanted plugs of 24 commonly grown cultivars of three species of warm-season turfgrasses subjected to varying amounts of

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David O. Okeyo, Jack D. Fry, Dale J. Bremer, Ambika Chandra, Dennis Genovesi, and Milton C. Engelke

) compared the establishment rate and stolon growth characteristics of five Z. japonica lines, ‘Emerald’, and a Z. matrella cultivar in Maryland. When planted as 5-cm diameter plugs on 30-cm centers, ‘Midwest’, a Z. japonica , and Bel-Zrt-1, an

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Marco Schiavon, Brent D. Barnes, David A. Shaw, J. Michael Henry, and James H. Baird

the existing sod and replacing sod of a warm-season species would be the ideal remedy, but this may be cost prohibitive for many homeowners and facilities. An alternative approach would be to seed or plug the warm-season species directly into the