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Thomas W. Zimmerman and Ralph Scorza

This study examined stage I peach shoot growth under various photoperiods in combination with different vessel closures and compared the influence of BA and Thidiazuron (TDZ) on peach shoot growth during stage II. The basal salts were as described by Almehdi and Parfitt (1986) with 1.0 μM BA, 0.02 μM IBA, 2% sucrose, 0.1% gelrite and 0.4% agar. Shoot growth of peach clone B612615, as determined by leaf number after one month, was similar in vessels capped with Kim-Kaps, Kaputs or PM caps. Plastic foam Identi-Plugs resulted in desiccation of the medium and stressed shoots with reduced growth. A 4 h light/2 h dark photoperiod four times a day provided better growth during stage I than a 16 h light/ 8 h dark photoperiod. For stage II, established shoots of Suncrest, Georgia Bell and Evergreen were grown on MS medium supplemented with 0.02 μM IBA in combination with 1.0 or 10 μM BA or 0.1, 1.0 or 10 μM TDZ. TDZ produced excessive callus resulting in minimal shoot proliferation. Shoot proliferation from axillary buds was greatest with 10 μM BA.

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Thomas W. Zimmerman and Jacqueline Kowalski

The Sandy Point Orchid (Psychilis macconelliae) is listed as an endangered orchid species by the U.S. Virgin Islands Dept. of Planning and Natural Resources. This orchid grows naturally on the southern dry and wind-swept slopes found on the east-end of St. Croix. It can be found growing among cacti and bromeliads. Due to disturbance to the native habitat from land development, private collectors, and natural disasters, the population has diminished. Tissue culture is being successfully used in a conservation effort for this endangered species. Maturing seed pods were collected and surface disinfested and established in vitro. The medium consisted of one half Murashige & Skoog salts, Nitsch & Nitsch vitamins, 20 g/L sucrose, 2 g/L soy peptone, 5 g/L activated charcoal and 8 g/L agar. Seeds were spread on the medium in 15 × 100-mm petri plates and grown at 25 °C under a 16-h photoperiod. Seed germination occurred within 2 months with the development of protocorms. Leaves and roots developed by 5 months, at which time they were separated and transferred to fresh medium. At 8 months, they were established in a greenhouse and released back into their environment within 12 months. In vitro germination of the Sandy Point Orchid seed is an effective way of conserving this endangered species.

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Thomas W. Zimmerman, Fredrick T. Davies, and Jayne M. Zajicek

Dyssodia pentacheta, a low growing perennial Texas wild flower with potential for use in low maitenance landscapes, was propagated in vitro and with cuttings under a mist system. Over 80% of both semihardwood terminal cutting from stock plants and in vitro grown nodal segments, dipped in 0, 3, 10, or 30 M-3 IBA, formed roots after 4 weeks under an intermittent mist system. A 300 M-3 IBA basal dip was lethal to the cuttings. Dyssodia produced significantly more shoots per nodal explant in vitro on semisolid (2 g l-1 Gelrite) WPM with 1-10 M-6 BA than combinations of BA and 0.5 M-6 NAA. Shoots were successfully subcultured and grown for two passes on semisolid growth regulator free medium. When maintaining Dyssodia in vitro on WPM, void of plant growth regulators, 1% sucrose promoted shoot growth and suppressed phenolic production better than 2% sucrose.

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Thomas W. Zimmerman, Fred T. Davies Jr., and Jayne M. Zajicek

Dyssodia pentacheta, a prostrate-growing perennial Texas wildflower with potential for use in low-maintenance landscapes, was propagated in vitro and by stem cuttings under mist. Optimum rooting for IBA-treated semihardwood terminal stem cuttings (3 to 30 mm IBA) and in vitro-grown nodal segments (30 to 100 mm IBA) occurred after 4 weeks under an intermittent mist system. A 300-mm IBA basal dip was lethal to macroand microcuttings. In vitro, D. pentacheta produced more shoots per nodal explant on Woody Plant Medium (2 g Gelrite/liter) with 1 to 10 μ m BA than with combinations of BA and 0.5 μm NAA. After shoot proliferation, the shoots were subculture twice and grown on growth regulator-free medium. When maintaining D. pentacheta in vitro on media devoid of plant growth regulators, 1% sucrose was more effective than 2% for promoting shoot growth and suppressing apparent production of phenolics. Chemical names used: N-(phenylmethyl) -1H-purin-6-amine (BA); 1H-indole-3-butyric acid (IBA); 1-naphthaleneacetic acid (NAA).