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Ellen B. Peffley and Melanie A. Hart

Particle bombardment was investigated as a potential transformation method for onion. Seeds of Allium cepa `TG 1015' were planted onto BDS medium and placed in a dark incubator at 25C for germination. Two to 3 weeks after the seeds were germinated, meristems (1 to 2 mm) were excised and placed onto BDS medium containing 2 mg 2,4-D/liter for callus initiation. Callus was transferred monthly onto fresh BDS medium containing 2,4-D until bombardment. The reporter gene for B-glucuronidase (GUS) expression was used to assess efficiency of gene delivery in all particle bombardments. Characteristics examined were target distance and helium pressure (particle velocity). Tissues were subjected to the 5-bromo-4-chloro-3-indoyl-B-D-glucuronide (xgluc) test for detection of GUS activity. Measurements were taken on particle dispersion as affected by target distance and helium pressure. GUS expression was detected in putatively transformed tissues.

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Michael Parker and Eric Young

Controlling vegetative growth resulting from a long growing season in the southeast is difficult while trying to promote early fruiting. This study was initiated in 1990 to evaluate higher density leader training techniques, cultivar interactions, and the benefits of pre-plant fumigation on apple replant sites. Another objective was to evaluate these management parameters in four regions with very different climates and elevations. The training techniques evaluated were, weak leader renewal, bending of the leader during the growing season, and partial terminal leaf removal every 10 inches of leader growth (without injuring the apical meristem). The cultivars used were Jonagored, Spur Gala, and Red Fuji, all on Mark rootstock. First and second year branching was not significantly different between the various training techniques. Yields during the third year did not appear to differ between the leader training techniques. Pre-plant fumigation appeared to be beneficial in increasing tree growth in only two of the four sites.

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Shailaja Sinha and Madhuri Sharon

Somatic embryogenesis from apical meristem, cell elongation zone, and cell differentiation zone of roots of Punica granatum L. var. Ganesh was obtained. The basal medium used was Gamborg's B5. 2, 4-D induced white globular callus in root tip explants, which on further subculture to medium containing 0.5 mg/L BAP, produced somatic embryos from the outer surface of the callus. Direct somatic embryogenesis occurred from all the three zones of the root in presence of 2 mg/L kinetin. BAP induced embryogenic callus in elongation and cell differentiation zone segments of the roots, which, on further subculture onto the same medium, produced somatic embryos. NAA caused rhizogenesis in all the three root segments. Differentiation of somatic embryos into plantlets took place on B5 medium supplemented with 0.01 mg/L NAA + 0.5 mg/l BAP + 2 mg/L kinetin.

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A. James Downer, Matthew Shaw, and Dennis Pittenser

Coast Live Oak (Quercus agrifolia) and White oak (Q. lobata) are landscape trees which are prone to sudden branch drop. The purpose of this work was to determine the effect of various pruning techniques on growth reduction of one member of a pair of codominant stems. Forty trees of each species were selected with codominant stems. One stem of each pair was pruned by: 1. removing all apical meristems; 2. thinning 50% of branches; 3. heading back to a 10cm stub or, 4. unpruned. Calipers of thinned or headed branches were most retarded while tipped and unpruned branches grew most. Results suggest that pruning by thinning may be an alternative to removal of codominant branches when training young trees.

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Sheila M. Colby, Adrian M. Juncosa, James A. Stamp, and Carole P. Meredith

The developmental anatomy of direct shoot organogenesis from in vitro leaves of Vitis vinifera L. cv. French Colombard was studied by light microscopy. Regenerating petiole stubs of leaf explants were fixed at intervals and were sectioned longitudinally to determine the developmental sequence of direct shoot organogenesis. After 6 days, three distinct regions of meristematic activity were apparent within expanding petiole stub: the wound-response, organogenic, and vascularization regions. In the organogenic region, divisions of vacuolate outer cortical cells formed nodular bumps that sometimes became adventitious leaves. Promeristems, which had the potential to become adventitious shoot meristems, were also initiated asynchronously in the organogenic region. Promeristem initiation occurred by two or several synchronous cell divisions occurring in the epidermal and subepidermal cell layers. Adventitious shoots and leaves developed new vascular bundles that connected to the pre-existing vascular bundles of the explant.

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Ryoichi Nakajima, Shungo Otagaki, Katsuhiro Shiratake, and Shogo Matsumoto

Previously, we showed that a reduction of FaTFL2 (homolog of Arabidopsis thaliana TFL1) expression is a key signal for flowering in domesticated octaploid strawberries (Fragaria ×ananassa). Since FaTFL2 expression seemed to be regulated by temperature rather than by photoperiod, we investigated whether down regulation of FaTFL2 and floral meristem generation occurred at different temperature conditions. In addition to the conditions for a normal super-forcing cultivation system of an 8-hour photoperiod and day/night temperatures of 31.2 or 30/15 °C, flowering also was generated under the same photoperiod and day/night temperatures of day/night-half/night-half temperatures of 30/15/25 °C conditions. We demonstrate that the new super-forcing cultivation system is energy saving based on the reduction of FaTFL2 expression.

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Caroline J. Poole, Audrey I. Gerber, and Gerard Jacobs

Brunia albiflora (Pillans) is harvested commercially in South Africa as a cut flower for export to European markets. To compete with European cut flowers high quality and continuity of product during the marketing period are essential. Optimizing the cut-flower potential of B. albiflora requires an understanding of the flowering process and selection of clonal material. We present a series of scanning electron micrographs which show three-dimensional images of the developmental stages of the shoot apex during the transition from the vegetative to the reproductive state. In B. albiflora the inflorescence consists of more than 15 individual rotund inflorescences arising from lateral positions on the terminal portion of the shoot. Development of the apical meristem of axillary shoots was studied to determine the time and sequence of inflorescence initiation and development. These observations identified that flower initiation occurs in October, followed by flower development through summer, with anthesis being reached from February to March.

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Setapong Lekawatana and Richard A. Criley

Inflorescence abortion in heliconia contributes to an economic loss to growers. In an effort to determine the cause, we manipulated temperature, daylength and light intensity. Plants of Heliconia stricta cv. Dwarf Jamaican were grown in 4 day/night temperature regimes (15/10, 20/15, 25/20 and 30/25°C) under 14 hr daylength. In a separate experiment, plants were grown in full sun, 60% and 80% shade. Both experiments had been conducted after inflorescences were induced (4 weeks of short days). Apical meristems were dissected weekly to follow inflorescence development. Leaf abscisic acid level was detected by an indirect ELISA. Significantly more inflorescences were aborted in plants grown under high temperature regimes than in plants grown under low temperature regimes and under different light intensity. Abscisic acid concentration increased in heliconia leaves under regimes that induced inflorescence abortion. The results could provide a mean to improve heliconia inflorescence production.

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E.B. Peffley, M. Hart, Z. Xiang, Z. Hiang, A. El-Sharif, N. Dong, and G.C. Phillips

Particle bombardment using the Bio-Rad PDS-1000/HE system is being investigated as a means to develop a stable transformation system for the bulb onion. Donor materials for bombardments included sterile meristems and radicals from newly germinated seeds, callus of Allium cepa `TG1015', `Sunlite', and `Buffalo', A. fistulosum `Heshiko', and suspension-cultured cell lines with confirmed regeneration capability, as well as regenerated plants of an F1 interspecific hybrid. Transient expression assays using the B-glucuronidase (GUS) reporter gene system were used to optimize the conditions for transformation. Various promoters combined with the GUS coding sequence were tested. Results indicate genotype specificity for promoter expression. Some tissue continued to exhibit GUS activity after several months in culture, indicating potential for achieving stable transformation of onion.

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Chamchuree Sotthikul and Pimchai Apavatjrut

Propagation of Curcuma roscoeana in vitro was done successfully by culturing 0.5 × 1.0 mm shoot tips from young buds onto modified MS (1962) + 0.25 mg·L–1 kinetin. The bud-derived new plantlets could be multiplied on a new medium. Stem explants 10 mm in size, measured from base of the plantlets longitudinally cut in half, were the most suitable culture explants providing 2.8 new healthy plantlets/cultured explant. Explants from 4, 6, and 8 weeks old plantlets were more suitable than those of 2 weeks old when grown on agar or in liquid medium. From a histological study, it was found that new buds developed from preexisting meristems. The buds, like root initiation, could also occur directly from initial culture explants, not through callus. The plantlets obtained could successfully be transferred into growing pots, having a 95% survival rate.