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  • Author or Editor: Stephen Garton x
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The applications of plant biotechnology in horticulture have been driven by an assortment of biological, economic and sociological factors such as plant health, vigor and uniformity, product quality, cost of propagule, productivity, cost effectiveness, and ethical and environmental concerns. As the potential of biotechnology to impact horticulture continues to grow, it empowers professional horticultural scientists to become knowledgeable about the development of biotechnology and to critically evaluate the possible impacts of future applications in horticultural crops. Current applications and trends in biotechnology will be reviewed and critically assessed.

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Studies were conducted to determine the response of cocoyam shoot tips, petioles, cotyledons and hypocotyls in various media for callus formation, adventitious shoot development and somatic embryogenesis. In all experiments, B5 basal medium or low N B5 were supplemented with various growth regulators.

High frequency adventitious shoot proliferation was obtained using cotyledons and hypocotyls in medium supplemented with 1 mg/l IBA and 0.5 mg/l TDZ. Embryogenic callus was obtained using shoot tips in media containing 1 mg/l Dicamba, hile somatic embryos were observed in media containing 0.3 mg/l 2, 4 - D and 1 mg/l Kinetin, using hypocotyl and petiole explants. The impact of these results on micropropagation of cocoyam is discussed.

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Phyllitis scolopendrium var. americana is a rare North American fern species whose range is being threatened by habitat alteration. Research efforts were undertaken to ensure survival of the southern population by applying horticultural techniques to propagate new plants for reintroduction. Several techniques were used to induce spore germination. Aseptic techniques included direct plating of spores onto agar medium in petri dishes and dusting spores into test tubes filled with liquid medium. Spores were spread onto soil samples taken from the fern habitats and onto various other propagation media. Prothalli grown in nutrient solution were transferred onto various nonsterile conventional horticultural media. Results indicated that germination in the nutrient solution and subsequent transfer of prothalli was more efficient and promoted survival of propagules compared to subculture from solidified medium.

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Two cultivars of Zinnia elegans, `Big Red' and `Sunrise Red', were grown hydroponically in two different nutrient solutions. The experiment was implemented in the greenhouse to assess affects of growth regulator treatments on growth and development of the plants. Heights of seedlings germinated in peat pellets were measured prior to placement in the hydroponic units. Plants were sprayed with five rates of either paclobutrazol or uniconazole. The experiment was laid out as a randomized complete-block design with four replicates of the treatments, which were factorial combinations of variables. Days to first flower were recorded for each plant. After 90 days, measurements were made of plant heights, flower bud numbers, and dry weights of shoot and root systems. Nutrient treatments affected all parameters observed. Growth regulator treatments affected plant heights. `Sunrise Red' produced more flower buds and earlier flowers than `Big Red'.

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Two cultivars of Tagetes erecta Marigolds—Hero Yellow and Safari Tangerine—were grown hydroponically in two different nutrient solutions. The experiment was implemented in the greenhouses on the campus of Alabama A&M Univ., from March to May 1995. The experiment was to assess the effects of growth and development of Marigolds. Heights of seedlings, germinated in grodan (rockwool) cubes were measured and placed randomly in the hydroponic units. Plants were drenched with five rates of either Paclobutrazol (Bonzi) and Uniconazole (Sumagic). The experiment was laid out as a randomized complete block design with either three or four replications of the treatment, which were factorial combinations of variables. After 75 days measurements were made of plants heights, flower bud numbers and dry weights of shoot and root systems. Shoot dry weights were affected by growth regulator treatments, variety, nutrient treatments and a combination of variety and nutrient treatments. Root dry weights were affected by nutrient treatments. Flower bud formation and numbers were affected by the combination of nutrient and variety. Heights were affected by growth regulator treatments, variety and nutrient treatments.

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Trees of jujube (Ziziphus jujuba), particularly older ones, root with great difficulty. A greenhouse experiment was conducted to assess the effects of two strains of Agrobacterium rhizogenes (A4 and TR105) on softwood cuttings from two trees—a tree 10 years old not currently bearing flowers, which we called “juvenile” because it still exhibited many juvenile characteristics; and a tree ≈70 years old containing many flower buds, which we called “mature”. The cuttings were collected on 11 May 1994 and trimmed to 7.5 cm. Both strain and source of cutting influenced inoculation success—TR105 was more responsive to A. rhizogenes than was A4 and the “juvenile” cuttings more responsive than “mature” cuttings. Strain TR105 was very effective in increasing rooting percentages and root number. “Juvenile” cuttings had better rooting percentages, greater root number, and greater root length than did “mature” cuttings. Agrobacterium rhizogenes exhibits great potential for rooting other difficult woody ornamental or fruit tree species as well.

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Jujube (Ziziphus jujuba) is a plant whose cuttings root with great difficulty. Several strains of Agrobacterium rhizogenes were tested on two segments (proximal and basal) of derooted jujube seedlings in the presence or absence of IBA for induction of roots in vitro. Strains of A. rhizogenes used were A4, A4pARC8, TR105, and R1000. Strain, segment of derooted seedling, and IBA influenced inoculation success. Strains A4pARC8 and TR105 were more infective than A4 and R1000. Basal segments were more responsive than proximal ones and 0.5 mg·liter–1 1BA had a positive effect on inoculation success. Agrobacterium rhizogenes and IBA were very effective in promoting root formation, root number, root length, and early root emergence. They worked synergistically, but were effective independently as well. A4pARC8 and TR105 were more effective than strains A4 and R1000, and generally more effective than IBA. lBA was unable to eliminate the differential response of the two segments for individual strains.

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Axillary and apical buds from five Cornus kousa cultivars (`Little Beauty', `Samaritan', `Heart Throb', `Rosabella', and `Christian Prince') were initially established on two basal media, woody plant medium (WPM) and woody plant medium/broad leaved tree medium (BW), amended with the following concentrations of 6–benzylaminopurine (BA): 0, 2, 4, and 8 μm. After explants were transferred at 4-week intervals for 28 weeks beginning in April, only microshoots of `Samaritan', `HeartThrob' and `Rosabella', were harvested from proliferating cultures and placed on rooting media. `Little Beauty' and `Christian Prince' did not perform well in multiplication phase of tissue culture and were excluded from further studies. Rooting media contained WPM or BW supplemented with either 1-naphthaleneacetic acid (NAA), indole-3-butyric acid (IBA) or indole-3-acetic acid (IAA) at the following concentrations: 0, 0.5, 1.5, 4.5, and 13.5 μm. Six weeks following rooting experiment, preliminary data were collected and results showed that total of nine plants rooted on both WPM and BW media supplemented with IBA, 17 plants rooted on media supplemented with NAA, and 14 plants rooted on media supplemented with IAA. These results indicated that NAA and IAA appeared to be better for root production on C. kousa cultivar microshoots than IBA. Additionally, WPM supported more root production, when compared to BW, even though both media resulted in rooted microshoots. Proliferating masses were placed on fresh medium with 2μm BA and were used again for the rooting projects.

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Abstract

Rapid clonal propagation of Alnus glutinosa was achieved in vitro using lateral buds excised from greenhouse grown, juvenile stock plants. Multiple shoot development occurred in 50% of the cultures after the first subculture (7–8 weeks after initial explanting) using a low salt, woody plant medium containing 1 μM 6-benzylaminopurine (BA). Microshoots were removed from pro-liferating tissues and rooted in a conventional potting medium under high humidity prior to establishment in the greenhouse.

Open Access

Axillary buds from a single Cladrastis kentukea tree were initially cultured on two media, woody plant medium (WPM) and Murashige and Skoog (MS) containing 0, 1, 2, or 4 μm 6–benzylaminopurine (BA). Cultures were transferred to fresh media every 4 weeks. Elongated shoots were harvested after 39 weeks and transferred to half-strength MS medium supplemented with the following concentrations of IBA: 0, 3, 30, 100, and 300 μm for 3 d, then returned to half-strength MS without growth regulators. Explants exposed to 300 μm of IBA produced significantly more roots (75%) compared to explants exposed to other treatments. Fifty-four and 45% of the microshoots rooted when exposed to 100 and 30 μm IBA, respectively. Only 4% of the microshoots rooted when exposed to 3 μm IBA and none of the control microshoots rooted. Although the 300 μm treatment yielded the most rooted plantlets, there was significantly higher terminal meristem abortion compared to other treatments. There were no statistical differences between the numbers of roots and total root length among all treatments. Additionally, all microshoots that rooted had lenticels, suggesting that presence of lenticel cambial activity can possibly improve rooting abilities of selected microshoots. Rooted microshoots were gradually acclimatized to nonsterile environment.

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