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W. Tietjen, P.J. Nitzsche, W.P. Cowgill Jr., M.H. Maletta, and S.A. Johnston

`Market Prize' and `Bravo' cabbage (Brassica oleracea Var. capitata L.), transplanted as peat plug and bareroot plants into a field naturally infested with Plasmodiophora brassicae, Woronin, were treated immediately after planting with a liquid or a granular surfactant. APSA 80™, applied in transplant water, significantly reduced percent clubbing and disease severity index (DSI) compared to control treatments. Miller Soil Surfactant Granular™ did not significantly reduce percent clubbing or DSI. There was a significant effect of cultivar on percent clubbing and DSI. There was no significant effect of transplant type on percent clubbing or DSI. This year's study culminates five years of investigation of surfactants for clubroot control. Specific surfactants have proven to be an effective control of clubroot in cabbage. Chemical names used: nonylphenoxypolyethoxyethanol (APSA 80™); alpha-alkanoic-hydro omega-hydroxy poly (oxyethylene) (Miller Soil Surfactant Granular™).

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Yoshiaki Kitaya, Genhua Niu, Maki Ohashi, and Toyoki Kozai

Artificial lighting is widely used in controlled environment plant production to enhance plant growth and quality. However, high light intensity with artificial lighting is costly, and often causes increase of leaf temperature and, thus, leaf burn. We investigated the effects of photosynthetic photon flux (PPF) and photoperiod on the growth and morphogenesis of lettuce plug transplants under ambient and enriched CO2 levels. Three days after seeding, the plants were cultured under four PPF levels (100, 150, 200, and 300 μmol·m–2·s–1), two photoperiods (16 and 24 hr), and two CO2 levels (400 and 800 μmol·mol–1) for 18 days in growth chambers. Light source was fluorescent lamps. The air temperature around the plants was kept at 20°C. The results showed that dry weight of the plants increased linearly as PPF and daily integrated PPF (product of PPF and photoperiod) increased under both CO2 levels. At the same daily integrated PPF, higher CO2 level and longer photoperiod led to higher dry weight of the plants. CO2 enrichment increased significantly dry weight of the plants. The ratio of T/R and specific leaf area of the plants decreased quadratically as daily integrated PPF increased under both CO2 levels. The ratio of leaf length to leaf width of the plants decreased quadratically as PPF increased under the two photoperiods and CO2 levels.

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Jack W. Buxton, Wenwei Jia, and Guoqiang Hou

The automatic subirrigation system consists of a capillary mat placed above a constant water level in a reservoir. The optimum mat height above the water level was established by slanting a flat surface so the difference in vertical height from one end of the surface to the other was 25 cm. A ground cover providing water movement but not root penetration was placed over the mat. The capillary mat extended beyond the lowest end of the slopped surface and into the reservoir, the mat at the lowest end of the slopped surface was at the same vertical height as the water in the reservoir and remained constantly saturated. Plug trays were placed at intervals of 2.5 cm in vertical height above the water level. An average of 96-100% germination was obtained with marigold, tomato, impatiens and pepper seed in trays placed 5-7.5 cm in vertical height above the water level. These seedlings continued to develop and reached transplanting stage quicker than other trays. The rate and % germination was less in trays placed on the surface nearer to the height of the water in the reservoir. Germination in trays above 12.5 cm was greatly reduced and seed that did germinate did not develop and eventually died.

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Allen M. Armitage

Plugs of Arabis `Spring Cham', Cerastium `Columnae', Salvia `Blue Queen', and Saxifraga `Purple Robe' (128 plugs/tray) were cooled at 2 to 3C for 0, 4, or 8 weeks. Plugs were potted in 10-cm containers and placed in warm (20C day, 17C night) or cool (10C day, 8C night) and provided with various long- and short-day combinations. In general, all taxa flowered more rapidly in the warm house, but were not significantly taller. Arabis showed no response to cooling or photoperiodic treatments, but Cerastium and Saxifraga had significantly longer internodes when subjected to increasing number of LD cycles. Plants of Salvia and Cerastium also flowered more rapidly when subjected to increasing cycles of LD, but height of Salvia and Arabis was reduced when LD were followed by SD. Other species of perennials will also be discussed.

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Holly L. Scoggins, Paul V. Nelson, and Douglas A. Bailey

Substrate solution testing is an essential management tool for greenhouse plug production. Current methods of plug solution extraction and testing can be confounded by subjective aspects of their techniques. The press extraction method (PEM) developed at North Carolina State University offers a convenient and timely method of solution extraction. The rooting substrate is brought to container capacity and after a period of one hour, pressing the plug surface with a finger or thumb is sufficient to expel the solution. This series of experiments serves to quantify possible variation that may occur in pH, Electrical conductivity (EC), and nutrient analysis from differing manual extraction forces. A modified press was designed to apply a range of force [53, 71, 89, 106, and 124 N (5.0, 6.7, 8.3, 10.0, and 11.6 lb/inch2)], and sampling protocol consistency was verified. For all three experiments, the range of extraction forces within a single fertilizer rate did not significantly affect solution pH or EC. When testing included a range of fertilizer rates, results were significantly different among the fertilizer rates, demonstrating the method's ability to detect changes in pH and EC resulting from increases in fertility levels. Nutrient analysis (NO3 -, NH4 +, P, K, Ca, Mg, Na, B, Cu, Fe, Mn, and Zn) of solution extracted from two different rooting substrates (peat-based and coir-based) showed no differences within substrates for the range of force treatments.

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Katsumi Ohyama, Koji Manabe, Yoshitaka Omura, Toyoki Kozai, and Chieri Kubota

To evaluate the potential use of a 24-hour photoperiod for transplant production in a closed system, tomato (Lycopersicon esculentum Mill.) plug transplants were grown for 17 days either under a 24-hour photoperiod with a photosynthetic photon flux (PPF) of 200 μmol·m-2·s-1 or under a 16-hour photoperiod with a PPF of 300 μmol·m-2·s-1, resulting in the same daily integrated PPF (17.3 mol·m-2). Air temperatures were alternated between 28 °C during the first 16 hours and 16 °C for the subsequent 8 hours of each day. Fresh weight, dry weight and leaf area were 41%, 25%, and 64% greater, respectively, under the 24-hour photoperiod than under the 16-hour photoperiod. Physiological disorders (e.g., chlorosis and/or necrosis) were not observed under the 24-hour photoperiod, probably due to the alternating air temperature. Floral development of plants originating from both treatments did not differ significantly. Electric energy use efficiency of the closed system was 9% greater under the 24-hour photoperiod than under the 16-hour photoperiod. These results suggest that using a 24-hour photoperiod with relatively low PPF can reduce both initial and operational costs for transplant production in a closed system due to the reduction in the number of lamps.

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Eric B. Bish, Daniel J. Cantliffe, and Craig K. Chandler

The demand for plug transplants by the Florida winter strawberry (Fragaria ×ananassa Duch.) industry may increase as water conservation during plant establishment becomes more important and the loss of methyl bromide fumigant makes the production of bare-root transplants more problematic. A study was conducted during the 1995-96 and 1996-97 seasons to determine the effect of container size and temperature conditioning on the plant growth and early season fruit yield of `Sweet Charlie' strawberry plants. Plants in containers of three sizes (75, 150, and 300 cm3) were grown in one of two temperature-controlled greenhouses (35 °C day/25 °C night or 25 °C day/15 °C night) for the 2 weeks just prior to transplanting into a fruiting field at Dover, Fla. Plants exposed to the 25/15 °C treatment had significantly higher average root dry weights at planting in 1995 and 1996 than did plants exposed to the 35/25 °C treatment. Plants exposed to the 25/15 °C treatment also had higher average fruit yields than the plants exposed to the 35/25 °C treatment (48% and 18% higher in 1995-96 and 1996-97, respectively). The effect of container size on plant growth and yield was variable. Plants propagated in the 150- and 300-cm3 containers tended to be larger (at planting) than the plants propagated in the 75-cm3 containers, but the larger container sizes did not result in consistently higher yields.

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Jeongwook Heo, Sandra B. Wilson, and Toyoki Kozai

An improved forced ventilation micropropagation system was designed with air distribution pipes for uniform spatial distributions of carbon dioxide (CO2) concentration and other environmental factors to enhance photoautotrophic growth and uniformity of plug plantlets. Single-node stem cuttings of sweetpotato [Ipomoea batatas (L.) Lam. `Beniazuma'] were photoautotrophically (no sugar in the culture medium) cultured on a mixture of vermiculite and cellulose fibers with half-strength Murashige and Skoog basal salts in a scaled-up culture vessel with an inside volume of 11 L (2.9 gal). CO2 concentration of the supplied air and photosynthetic photon flux on the culture shelf were maintained at 1500 μmol·mol-1 and 150 μmol·m-2·s-1, respectively. Plantlets grown in forced ventilation systems were compared to plantlets grown in standard (natural ventilation rate) tissue culture vessels. The forced (F) ventilation treatments were designated high (FH), medium (FM), and low (FL), and corresponded 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. On day 12, the photoautotrophic growth of plantlets was nearly two times greater with the forced ventilation system than with the natural ventilation system. Plantlet growth did not significantly differ among the forced ventilation rates tested. The uniformity of the plantlet growth in the scaled-up culture vessel was enhanced by use of air distribution pipes that decreased the difference in CO2 concentration between the air inlets and the air outlet.

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Stephanie E. Burnett, Svoboda V. Pennisi, Paul A. Thomas, and Marc W. van Iersel

Polyethylene glycol 8000 (PEG-8000) was applied to a soilless growing medium at the concentrations of 0, 15, 20, 30, 42, or 50 g·L-1 to impose controlled drought. Salvia (Salvia splendens F. Sellow. ex Roem & Shult.) seeds were planted in the growing medium to determine if controlled drought affects morphology and anatomy of salvia. Polyethylene glycol decreased emergence percentage and delayed emergence up to 5 days. Stem elongation of salvia treated with the five lowest concentrations was reduced up to 35% (21 days after seeding), and salvia were a maximum of 53% shorter and the canopy was 20% more narrow compared to nontreated seedlings 70 days after seeding. These morphological changes were attributed to PEG-8000 mediated reduction in leaf water potential (Ψw). The growing medium Ψw ranged from -0.29 to -0.85 MPa in PEG-8000 treated plants, and plant height was positively correlated with Ψw 21 days after seeding. Stem diameter of PEG-treated seedlings was reduced up to 0.4 mm mainly due to reductions in vascular cross-sectional area. Xylem cross-sectional area decreased more than stem and phloem cross-sectional area. Polyethylene glycol 8000 reduced vessel element number, but not diameter.