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Kay Oakley, Robert Geneve, Sharon Kester, and Myra Stafford

Root and shoot development in Marigold `Little Devil Flame' was studied after being grown for varying lengths of time in 392-count plugs before transplanting to six-pack cells. Seedlings were grown for 0, 5, 10, 15, 20, and 25 days before transplanting to six-packs. All plants were measured at day 25. There was no significant difference in total root length, area and dry weight per plant or in leaf area and shoot dry weight per plant for seedlings transplanted from 0 to 15 days. Both total root dry weight and total shoot dry weight of seedlings transplanted on day 20 was reduced by 32% compared to seedlings that were not transplanted. Total root dry weight of seedlings transplanted at day 25 was reduced by 60% while total shoot dry weight of seedlings was reduced by 56% from those not transplanted. In a separate experiment, the growth rate of seedlings grown in plugs was sigmoidal (r 2 = 0.98). Growth rate was significantly reduced between 20 and 25 days in the plug. These results suggest that root restriction in the plug may be a factor in the reduction of seedling growth following transplanting.

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Fumiomi Takeda Takeda, Stan Hokanson*, John Enns, Penelope Perkins-Veazie, and Harry Swartz

`Chandler' strawberry plants were propagated in tissue culture and grown from April to August in a protected environment to produce stolons. July-harvested daughter plants were stuck in cell packs with rooting media and placed under mist sprinklers, or cold stored at 2 °C for 42 days. Among the July transplants, some were kept in the greenhouse until field planting (14 Sept.) and others were moved into a cold room on 14 August. Daughter plant size and position on the stolon affected rooting and quality of transplants. July-harvested daughter plants that were plugged and misted after being cold stored for 42 days developed fewer roots than daughter plants plugged immediately after detaching from mother plants in July or August. In the field, transplants produced from daughter plants harvested in July and cold stored for 42 days developed more stolons than transplants from July- and August-harvested daughters that were not exposed to cold storage treatments. Larger daughter plants produced more branch crowns than did smaller daughter plants during the fall. All transplants from daughter plants harvested in July and propagated without cold treatment bloomed by November. Fruit production ranged from 521 to 703 g per plant. `Chandler' plants from daughter plants that weighed 10 g produced 10% greater yield than those that weighed <1.0 g. Plants generated from daughter plants plugged in July produced 26% more fruit than those plants plugged in August. Greenhouse soilless systems can be used to grow `Chandler' mother plants for generating runner tips and transplants for the annual plasticulture in colder climates. `Chandler' plants produced in July can yield a late fall crop under high tunnels and more fruit in the spring than August-plugged transplants

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Chin-Chang Chu and Kenneth W. Mudge

Rockwool plugs were placed in Magenta G-7 boxes (Sigma) and then autoclaved at 121°C for 20 min. Fifty milliliters of cool autoclaved liquid medium was poured into Magenta G-7 boxes in aseptic conditions before microcuttings of Amelanchier, Cercis canadensis, cherry, and apple were transferred. Murashige and Skoog medium (MS, M-5519, Sigma) containing 30 g·L–1 sucrose, and with/out 1 ppm of NAA, pH 5.5 were used in all experiments. All cultures were incubated at 23 ± 1°C under a 16-hour lighting period with a light intensity of about 4000 lux of white fluorescent light. Microcuttings of Amelanchier, Cercis, Apple, and cherry rooted in rockwool plugs in 3 weeks after transfer and were ready to be out-planted in 6 weeks. Out-planted plantlets were leached with tap water and potted in 4-inch pots with Metrolite mix, then, placed in mist bench under 50% shade for 2 weeks before taking to bench with full sun light. The survival was 100%. Conditions and growth rate of rockwool-plug-rooted plantlets were much better than those plantlets rooted in agar medium. Rockwool plug plantlets had 2–3 flushes of growth before dormancy in greenhouse and were ready to be planted in the field or garden in 8 months after out-planting. Using a rockwool plug system simplifies out-planting procedure, produces better plantlets, increases out-planting survival, and greatly shorten time needed from out-planting to field-plantable size. This system is a very useful system for difficult-to-root woody ornamentals.

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Junne-Jih Chen, Yung-Wei Sun, and Tzay-Fa Sheen

Seedlings of tomato (Lycopersicon esculentum Mill.) and cabbage (Brassica oleracea L. var. Capitata) were planted in 240-cell plug trays in the greenhouse and subjected to irrigation with water at different temperatures once a day. Irrigation with cold (5 to 15 °C) water reduced stem length of tomato by 28% to 32% in comparison with irrigation with water at room temperature (27.5 to 30.5 °C). Use of water at 10 °C did not affect total shoot dry weight but increased the shoot dry weight per centimeter of stem. Irrigation with water at 5 °C reduced stem length of cabbage seedlings 40%, but use of water at 10 and 15 °C did not. Both shoot and root dry weights were increased by irrigation with water at 10 °C. These results demonstrate that irrigation with cold water provides an effective method for improving the quality of plug-grown seedlings.

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Erik S. Runkle and Royal D. Heins

Environments with a low red (R, 600 to 700 nm) to far-red (FR, 700 to 800 nm) ratio (e.g., with high plant density) promote stem elongation, and a high R: FR suppresses it. While FR light promotes stem extension, it is also required for rapid, uniform flowering of many long-day plants. We investigated how a new FR filter [creating a FR-deficient (FRd) environment] influenced plug growth and subsequent flowering of pansy (Viola ×wittrockiana `Crystal Bowl Yellow'), petunia (Petunia ×hybrida `Carpet Pink'), impatiens (Impatiens wallerana `Accent Rose'), snapdragon (Antirrhinum majus `Liberty Scarlet'), and tomato (Solanum lycopersicon `Beefmaster'). One-week-old seedlings were placed under three filter treatments with 16-h photoperiods: the FRd filter, a neutral-density filter (N) that transmitted a similar PPF, and transferring plugs from the N to the FRd filter when leaves of each species began to touch (7 to 11 days later). The predicted phytochrome photoequilibria under the FRd and N filters was 0.80 and 0.72, respectively. After 25 to 35 days at 20 °C, node number and stem (or petiole for pansy) length were collected. Twenty plants of each species and filter treatment were then transferred to 4-inch pots and grown under natural photoperiods (14 to 15 h) at 20 °C until flowering. Compared to plants continually under the N filter, stem length under the FRd filter was significantly reduced in impatiens (by 11%), pansy (by 18%), petunia (by 34%), snapdragon (by 5%), and tomato (by 24%). Flowering of plants from plugs under the FRd filter was delayed by 2 to 3 days for snapdragon, petunia, and pansy. Filter treatment of plugs had no significant effect on flower number or plant height at flower.

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A.M. Armitage and P.M. Gross

A copper hydroxide formulation (0%, 3.5%, 7%, 11% Cu) was applied to plug trays before sowing seeds of Impatiens ×hybrida L. `Accent Red', Pelargonium ×hortorum Bailey `Scarlet Elite', and Petunia ×hybrida Hort.Vilm.-Andr. `Ultra White' to investigate the influence of the formulations on ease of transplant, root growth, and shoot growth. These factors also were investigated in Cu-treated seedling plugs held past optimal transplanting stage. Root spiraling and seedling height at transplant were reduced for all taxa grown in Cu-treated trays, regardless of concentration, compared to seedlings from nontreated trays. Root weight and shoot weight responses to Cu treatments at transplant and at flowering varied among taxa. Mature heights of all taxa were unaffected by Cu treatment; however, flowering date was delayed for impatiens and geraniums transplanted at optimal time from Cu-treated trays. In general, petunias displayed little response to Cu treatment. Root spiraling was reduced and plugs were removed more easily from Cu-treated than from control trays stored for 2 weeks in the greenhouse, but flowering time was delayed for 12 days for impatiens and petunias and 21 days for geraniums, regardless of Cu concentration.

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M.W. van Iersel, R.B. Beverly, P.A. Thomas, J.G. Latimer, and H.A. Mills

Good fertilizer management is important in plug seedling production of bedding plants to prevent nutrient deficiencies and toxicities. We determined the effect of N, P, and K nutrition on the growth of plugs of impatiens (Impatiens wallerana Hook. f.), petunia (Petunia ×hybrida Hort. Vilm.-Andr.), salvia (Salvia splendens F. Sellow ex Roem.& Schult.), and vinca (Catharanthus roseus L.). For all four species, shoot N concentration was correlated linearly with shoot dry mass of the seedlings at transplant. Phosphorus or K concentration in the nutrient solution or shoot tissue had little or no effect on the shoot growth of seedlings, but shoot P levels increased with P concentrations in the fertilizer solution (luxury consumption). Salvia was the only species that also exhibited luxury consumption of K. Results of this study indicate that seedling growth of these species is mainly determined by N and this should probably be the main focus of fertility programs in the plug industry, while P and K applications can be reduced.

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Robert L. Geneve, Jack W. Buxton, and Myra Stafford

Capillary mat subirrigation provides uniform water in the growing medium to optimize seedling growth in plugs. It also offers a closed system that allows the grower to regulate the amount of water available to seedlings and to reduce water runoff. However, root outgrowth into the capillary mat can be a significant problem. Copper hydroxide (Spin Out) was painted on the bottom, outside surface of the plug container to control root outgrowth into the capillary mat. Three square and two octagonal plug sizes were treated with copper. Regardless of the plug size or shape, copper treatment was an effective treatment to control root outgrowth in marigold seedlings. Copper treatment reduced overall root outgrowth by 80% to 92%. Marigold and geranium seedlings in copper-treated square plug containers showed some reduced shoot and root development during plug production, but there were no differences in copper-treated plants compared to nontreated plants following transplanting to cell packs.

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

A greenhouse hydroponic system, which uses suspended plastic troughs, was found to be an efficient system for the production of high quality strawberry (Fragaria ×ananassa) plantlets. In this system micropropagated mother plants of `Oso Grande' and `Sweet Charlie' produced an average of 84 and 80 daughters per mother plant, respectively, in 1996, at a plant density of 3 mother plants/ft2 (32 mother plants/m2). Nearly 100% of the plantlets harvested from the system were successfully rooted in plug trays, and showed no symptoms of leaf or crown diseases.

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Mark P. Kaczperski, Allan M. Armitage, and Pamela M. Lewis

Seed of Viola × wittrockiana `Majestic Giant Yellow' were germinated in #406 plug trays at ambient CO2, 25 C and a light intensity of 100 μmol s-1m-2 with an 18 hr photoperiod. At emergence and at successive one week intervals, seedlings were exposed to CO2 levels of 500, 1000 or 1500 μl l-1 and irradiances of 100, 225, 350 μmol s-1m-2 for 7 to 35 days, after which seedlings were transplanted into 10 cm pots and grown to flower in the greenhouse. CO2 at 1000 μl l-1 was as effective as 1500 μl l-1 in accelerating growth in the plug stage. 500 μl l-1 at all irradiances did not accelerate growth significantly. Plants grown at 1000 μl l-1 and 225 μmol s-1m-2 intensity reached the 5 leaf stage up to 14 days earlier than the control, as well as decreasing time to flower during the growing on phase.