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A. Raymond Miller and Craig K. Chandler

A protocol was developed for excising and culturing cotyledon explants from mature achenes of strawberry (Fragaria × ananassa Duch.). Cotyledon explants formed callus with multiple shoot buds on agar-solidified Murashige and Skoog media containing several combinations of hormones (1 μm 2,4-D; 10 μm 2,4-D; 1 μm BA + 1 μm 2,4-D; 1 μm BA + 10 μm 2,4-D; 5 μm BA; 5 μm BA + 1 μm 2,4-D; 5 μm BA + 10 μ m 2,4-D; 5 μ m BA + 5 μm NAA; 5 μ m BA + 15 μ m NAA). After three subcultures, only tissues maintained on the medium containing 5 μm BA + 5 μm NAA continued to form shoots. Tissues transferred to other media eventually died (1 μm 2,4-D; 1 μ m BA + 10 μ m 2,4-D; 5 μ m BA; 5 μ m BA + 1 μ m 2,4-D), became unorganized (1 μm BA + 1 μm 2,4-D; 5 μm BA + 10 μm 2,4-D; 5 μm BA + 15 μm NAA), or formed roots (10 μm 2,4-D). Whole plantlets were produced by transferring callus with buds to medium lacking hormones. The rapid regeneration of clonal plantlets from cotyledon explants may be useful for reducing variability in future developmental studies. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); (2,4-dichlorophenoxy) acetic acid (2,4-D); and 1-naphthaleneacetic acid (NAA).

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Michael E. Kane and Craig K. Chandler

Many horticultural crops are infected with bacterial, fungal, or viral pathogens that reduce yield and/or quality. Recovery and maintenance of pathogen eradicated crops, such as strawberry (Fragaria × ananassa Duch.), have been possible following the isolation and culture of apical meristems or meristem-tips in vitro. A laboratory exercise has been developed to provide experience in the procedures required for the isolation, surface disinfection, and in vitro establishment of meristem-tip explants excised from strawberry stolons. Stolons are obtained from greenhouse-grown strawberries (`Sweet Charlie') maintained in hanging baskets under a 14-h photoperiod. Stolons are cut into single-node segments and terminal tips. The leaf blades are removed and the nodal sections are rinsed and then surface-disinfected by successive agitation in 70% ethanol and 1.05% sodium hypochlorite, followed by three rinses in sterile deionized water. In the transfer hoods, each student attempts to isolate meristem-tips and shoot tips of various sizes under high magnification provided by a stereomicroscope. Explants are inoculated onto Murashige and Skoog basal medium (Murashige and Skoog, 1962) supplemented with 30 g/liter sucrose, 80 mg/liter adenine sulfate, 1.0 mg/liter benzyladenine, 1.0 mg/liter indole-3-acetic acid, and 0.01 mg/liter gibberellic acid (GA3) and solidified as 45°slants with 1.25 g/liter Phytagel and 3.0 g/liter TC agar. Growth responses are monitored weekly. After 6 weeks, students record the percentage of visibly contaminated cultures and number shoots produced per explant. The relationship between initial explant size and in vitro growth is also determined. Students index their cultures for the presence of cultivable bacteria and fungi using sterility test media.

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Earl E. Albregts and Craig K. Chandler

Four strawberry (Fragaria ×ananassa, Duch.) cultivars were grown in a winter strawberry fruiting study using the annual hill cultural system and polyethylene-mulched beds during two seasons. Plants were set on 15, 30, 45, and 60 cm in row-plant spacing with two rows per bed spaced at 45 cm. Increasing plant density in the fruiting field generally increased early fruit yield and sometimes total fruit yield during two seasons. Yields of cull fruit were also increased with increased plant density. Daughter plant production decreased with increased plant density. Growers should consider planting costs, fruit rot, and harvesting problems when selecting the plant density for fruit production.

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Craig K. Chandler, T. E. Crocker and E. E. Albregts

During the past 10 years, the Florida strawberry growers, through the Florida Strawberry Growers Association, have made a serious commitment to fund university research on strawberries. They have purchased equipment and donated monies for facilities at Dover. They have also helped support a new faculty position in breeding and genetics. During this same period, the University of Florida has made an equally strong commitment to support strawberry research and extension. These commitments are beginning to pay significant dividends for industry and the University. Cultural and pest management information has been generated that is saving the industy money, and the breeding program is developing new cultivars that will keep the industry competitive in the marketplace. The University has benefitted through the acquisition of new facilities, equipment, and faculty and graduate student support.

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Craig K. Chandler, Daniel E. Legard and Charles A. Sims

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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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George J. Hochmuth, Earl E. Albregts and Craig K. Chandler

During the 1992-93 fruiting season, strawberries were fertigated weekly with 0.28, 0.56, 0.84, 1.12, or 1.40 kg N/ha/day from ammonium nitrate. K was applied uniformly at 0.84 kg/ha/day by fertigation. Irrigation maintained soil moisture tension in the beds between -10 and -15 kPa. Fruit yields responded positively to N fertilization with yields maximized at 0.56 kg N/ha/day. Leaf N and petiole sap nitrate N concentrations increased with N rate with leaf-N for the plants receiving 0.28 kg N/ha/day remaining below 25 g·kg-1 most of the season. Sufficiency ranges for petiole sap nitrate-N quick testing were developed.

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Craig K. Chandler, Diane Doud Miller and David C. Ferree

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

Containerized strawberry transplants offer an alternative to problematic bare-root transplants, which often have variability in flowering and vegetative vigor. Containerized transplants were propagated in three different container cell sizes (75, 150, and 300 cm3) and grown at two different temperature regimes for 2 weeks prior to planting (25/15 and 35/25°C day/night). Bare-root transplants from Massachusetts and Florida were graded into small, medium, and large plants based on crown size (8, 12, and 16 mm respectively). Plug transplants grown at 25/15°C had greater root dry weights than transplants grown at 35/25°C. Root imaging analysis (MacRHIZO) showed that the differences in dry weight were due to root area, not root tissue density. Crown dry weight increased with increasing cell size. Plug transplants grown at 25/15°C flowered earlier and had greater production than any other treatment. The 75 cm3 cell size grown at 35/25°C produced greater December strawberry production than larger cell sizes at the same temperature regime; however, the 75 cm3 cell size had decreased January strawberry production while the larger cell sizes had increased production. Larger plug cell sizes had significantly greater production than smaller plugs throughout the season, whereas larger bare-roots had greater production only early in the season. Containerized plug transplants therefore offers a viable alternative to problematic bare-root transplants.