Several methods have been published on shoot regeneration from watermelon cotyledon explants. The major differences in regeneration protocols include the light environment in which seeds are germinated and the cotyledon region used. The purpose of these experiments was to compare the two main protocols for plant regeneration and develop one general procedure. To fulfill this objective, seeds were germinated in vitro in darkness or 16-hr light photoperiod for 7 days. Cotyledon explants from four watermelon cultivars (`Crimson Sweet', `Minilee', `Sweet Gem', and `Yellow Doll') were prepared from both dark- and light-grown seedlings. Apical and basal halves were obtained by making a cut across the cotyledon width. Apical and basal quarters were made, for comparison, by cutting apical and basal halves longitudinally. All explants were incubated on shoot regeneration medium for 6 weeks followed by a 3-week cycle on shoot elonga-tion medium. The percentage of cotyledons with shoots was 1.7-fold greater for cotyledons derived from seedings incubated in darkness than those germinated in light. Shoot formation was about 10-fold greater for explants from cotyledon basal halves and quarters than apical halves and quarters. According to these results, the best watermelon regeneration protocol should consists of basal explants from in vitro-germinated seedlings incubated in the dark for 7 days.
Abstract
Tissue culture propagation of Senecio cruentus DC. ‘Hansa’ was achieved from shoot tips derived from selected seedlings germinated in vitro. Shoot multiplication was best accomplished on Murashige and Skoog (MS) gerbera medium supplemented with 2.8 μM IAA. Maximum root formation occurred on MS modified medium with reduced salt levels and 1.3 μM NAA. Rooted shoots were established successfully in a soilless medium under high humidity. Chemical names used: 1H-indole-3-acetic aid (IAA); 1-naphthaleneacetic acid (NAA).
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Kankakee mallow is an endangered herbaceous perennial that is indigenous to Kankakee County, Illinois. Stock plants were from seeds pretreated in 82°C water prior to greenhouse germination and growth. Nodal explants were disinfested and placed in vitro onto agar-solidified MS medium containing 0, 0.1, 1.0, 5.0, or 10.0 μM BA and 1.0 μM IBA. Axillary shoots grew and elongated best when the medium contained no cytokinin. BA tended to result in a rosette pattern of leaves. Within hours of placing the original explants in vitro and shortly after subsequent transfers were made (even when there was no cutting) a bright pink exudate appeared in the medium. The most vigorous cultures tended to form the most exudate. Microshoots were placed in a high humidity container in vermiculite wetted with water. Rooting was 50% without auxin. Plants were transplanted into pots containing peat-lite medium and successfully acclimatized to the greenhouse.
Although somatic embryogenesis in vitro has been carried out successfully in a number of plants, a limiting factor in many somatic embryogenic systems is that plantlet regeneration is not obtainable or restricted to low frequencies. We have developed a repetitive, high frequency somatic embryogenic system in pecan (Carya illinoensis) and have identified effective treatments for improved somatic embryo conversion. A 6 to 10 week cold treatment followed by a 5 day desiccation, promoted enhanced root germination and extension, and epicotyl elongation. Light and transmission electron microscopic evaluations of somatic embryo cotyledon development will be presented and related to conversion enhancing treatments and their possible roles in embryo maturation.
Although somatic embryogenesis in vitro has been carried out successfully in a number of plants, a limiting factor in many somatic embryogenic systems is that plantlet regeneration is not obtainable or restricted to low frequencies. We have developed a repetitive, high frequency somatic embryogenic system in pecan (Carya illinoensis) and have identified effective treatments for improved somatic embryo conversion. A 6 to 10 week cold treatment followed by a 5 day desiccation, promoted enhanced root germination and extension, and epicotyl elongation. Light and transmission electron microscopic evaluations of somatic embryo cotyledon development will be presented and related to conversion enhancing treatments and their possible roles in embryo maturation.
Platanthera praeclara, commonly called western prairie fringed orchid, is a showy forb native to seven states and one Canadian province. The species had resisted previous attempts at propagation. Small, isolated populations in the sandhills region of western Nebraska are disjunct and visitation by natural pollen vectors appears to be in decline. Modern cultivation practices and other habitat encroachment factors, including urban development, recreational activities, and natural fluctuations in seasonal water availability all have the potential to exert pressure on current populations. Federal and state permits have allowed a limited hand-pollination study to be conducted on federal land. Hand-pollinated plants showed a greater fruit production compared to control plants receiving no human pollination assistance. Germination studies were conducted using aseptic in vitro techniques. The microscopic seeds possess testa that are extremely hard and resistant to liquid absorption, which presents challenges to germination in vitro. These challenges will be discussed. Alternating cold treatments with room temperatures appeared necessary to promote protocorm development after germination. Three media tested produced varying germination responses. Juvenile plants produced through micropropagation can offer propagules for possible future reintroduction efforts of this protected species.
Cultures of several orchid species [Barlia robertiana (Loisel.), Dactylorhiza fúchsii Soó, D. incarnata (L.) Soó, D. maculata (L.) Soó, D. majalis (Rchb.), D. saccifera (Brong) Soó, D. sambucina (L.) Soó, Gymnadenia conopsea (L.) R.Br., Himantoglossurn hircinum (L.) Spreng., Ophris sphegodes Mill., Orchis coriophora ssp. fragrans L., Orchis laxiflora ssp. palustris Lam., Orchis mascula L., Orchis morio L., Platanthera bifolia (L.) Rich., Spiranthes aestivalis (Poir.) Rich.] were initiated with fresh ripe seeds from desiccated fruit and 4-month-old in vitro seedlings. The medium used for both germination and seedling culture was a modified FAST medium. Samples for the scanning electron microscope (SEM) surveys were taken from the in vitro cultures and some plant materials were collected from their native habit. Samples were observed with a Tesla BS 300 SEM. Seeds ranged from 300 to 450 μm in length and were flask-shaped. The first germination step is opening of the seedcoat, when the first few white cells will be visible. After a few weeks, the apical meristem appears. The young protocorm is covered with numerous translucent rhizoids. In the last stage of germination, the first root and the first true leaf start to develop. After 2 years, they are suitable for transfer ex vitro. Structure of the mature organs and tissues can be examined at this stage.
We gratefully acknowledge financial support for this study by the Spanish FEDER-CICYT Project 1FD97-0620-CO2-01. We thank David W. Schofield for helpful suggestions while translating the manuscript. Use of trade names in this publication does not
Abstract
Trees and fruit of 6 early ripening cultivars of peach and nectarine [Prunus persica (L.) Batsch] were sprayed about 4 weeks prior to commercial harvest with either butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide), maleic hydrazide, or thiourea. The date of 50% drop of overripe fruit was retarded one to 4 days. Chemical treatments increased germination of in vitro embryo culture of ‘Fla. 3-1’ and ‘Flor-daking’ up to 27-32%. Seed germination from cracked pits of ‘Fla. 7-3N’, ‘Fla. 7-4N’, ‘Earligrande’, and ‘Fla. M6-6N’ generally increased up to 50%. The delayed fruit drop did not appear to account for all of the increase in germination. The results support an enhancement of embryo development in addition to that attributed to delayed fruit maturity.