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Michael E. Compton and D.J. Gray

Adventitious shoots were obtained from watermelon [Citrullus lanatus (Thunb.) Matsun. & Nakai] cotyledons incubated on a modified Murashige and Skoog medium containing BA. Initial experiments comparing the effects of BA (0, 5, 10, or 20 μm) and IA4 (0, 0.5, or 5 μm) demonstrated that BA was required for adventitious shoot formation but its concentration in the medium was not critical. The addition of IAA to medium with BA increased callus production and inhibited shoot formation. However, the percentage of responding explants in the best treatment was <30%. Therefore, the manner in which cotyledon explants were prepared and seedling age at the time of explantation was examined to improve the organogenic response. The percentage of explants with shoots was improved by using explants that consisted of cotyledon bases (43%) or cotyledons cut in half longitudinally (39%). A lower percentage (16%) of cotyledons cut longitudinally into four pieces produced shoots. Explants taken from the apical half of cotyledons failed to regenerate shoots. Shoot formation was improved further by using explants from young seedlings. The percentage of explants with shoots was >90% for `Minilee', 64% for S86NE, and 50% for `Jubilee II' when explants were prepared from 5-day-old seedlings. Explants from nongerminated embryos or seedlings germinated for 10, 15, or 20 days produced fewer shoots. The effect of several cytokinins on shoot organogenesis was then examined using the optimized protocol. The percentage of explants with shoots and the number of shoots per explant were about two to four times higher when 5 to 10 μm BA was used compared to the most effective kinetin (20 μm) or thidiazuron (0.1 μm) concentration. The percentage of explants with shoots and the number of shoots per explant were greater for diploid (57% and 2.2, respectively) than for triploid (22% and 0.6, respectively) or tetraploid (20% and 0.8, respectively) lines. Chemical names used: N -(phenylmethyl)-1 H -purin-6-amine (BA); 6-furfurylaminopurine (kinetin); N -phenyl-N' -1,2,3-thiadiazol-5-ylurea (thidiazuron); 1 H -indole3-acetic acid (IAA).

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N.J. Gawel, C.D. Robacker, and W.L. Corley

Immature inflorescences of Miscanthus sinensis Andress. `Gracillimus', `Variegatus', and `Zebrinus' were cultured on modified MS medium with 9.0 μm 2,4-D, 20 g sucrose/liter, 2.0 g Gelrite/liter, and 0.75 g MgCl2/liter. Organogenesis was observed 8 to 12 weeks after callus initiation. Shoots were rooted on half-strength MS medium without growth regulators. After rooting, tillers were initiated. When transferred to soil, plants matured to flowering quickly and retained their variegation patterns. Propagation through in vitro tillering is suggested. Chemical name used: 2,4-dichlorophenoxyacetic acid (2,4-D).

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Xiaojuan Zong, Brandon J. Denler, Gharbia H. Danial, Yongjian Chang, and Guo-qing Song

hormonal content and somatic organogenesis in callus of peach ( Prunus persica L. Batsch) cultivars and Prunus persica × Prunus dulcis rootstocks J. Plant Physiol. 171 619 624 Pérez-Jiménez, M. Carrillo-Navarro, A. Cos-Terrer, J. 2012 Regeneration of

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Jane Kahia, Peter Kanze Sallah, Lucien Diby, Christophe Kouame, Margaret Kirika, Simeon Niyitegeka, and Theodore Asiimwe

Correia et al. (2011) . However, there are no documented studies on the direct organogenesis in Tamarillo. An important advantage of direct organogenesis is the potential for maintaining genomic stability of regenerated plants, whereas regeneration via an

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Yu-Tsung Lin, Chia-Wei Lin, Chien-Hung Chung, Mei-Hsiu Su, Hsiu-Yin Ho, Shi-Dong Yeh, Fuh-Jyh Jan, and Hsin-Mei Ku

) and shoot primordia formation through organogenesis on NAA/BA or NAA/zeatin combinations ( Punja et al., 1990 ). In this study, a successful organogenic regeneration procedure (with greater than 58% efficiency) for C. metuliferus is described

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Rajendra Maurya*, Nathu Ram Godara*, and Ram C. Yadav*

Influence of culture media and hormone concentrations on plant regeneration from rose (Rosa hybrida L. cv. Raktagandha) leaf segments were investigated. Leaves were excised from healthy, well-grown and mature plants. Leaf segments (4-5 mm long) were sectioned and cultured on Murashige and Skoog (1962) medium containing different concentration of growth hormones. Callus formation was most prolific (97.09%) on MS medium containing MS basal salts + 0.5 mg·L-1 BAP + 2.0 mg·L-1 2,4-D. maximum (56.67%) organogenesis or shoot differentiation was achieved on MS modified medium supplemented with 1.0 mg L-1 BAP + 0.1 mg·L-1 NAA + 10.0 mg·L-1 Adenine Sulphate. The highest percentage (93.73%) of in-vitro rooting was observed in half-strength MS basal medium containing 0.5 mg·L-1 IBA. Rooted plants were transferred in to sterilized potting mixture and grown in a greenhouse.

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Rita M. Moraes-Cerdeira, Jeffrey V. Krans, James D. McChesney, Ana M.S. Pereira, and Suzelei C. Franca

Cotton fibers were tested as a substitute for agar in tissue culture. The cost of agar has prompted us to search for an alternative more economical medium support. Effectiveness as a medium support was evaluated in terms of callus maintenance and shoot organogenesis using Artemisia, Agrostis, and Taxus. Taxus and Agrostis calli cultivated on liquid media with cotton fiber as medium support (25 ml of medium per gram of cotton) grew better than calli on agar (0.8% w/v). There were no significant differences in shoot organogenesis of Artemisia and Agrostis grown in 25 ml of medium per gram of cotton from those grown in agar medium.

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Les Frey and Jules Janick

Shoot regeneration in carnation (Dianthus catyophyllus L.) was influenced by genotype, explant source, and plant growth regulator balance. Plants were regenerated from petals, calyxes, nodes, internodes, and leaves, but only petals, calyxes, and nodes were regenerative from all three cultivars examined (`Scania', `Improved White Sire', `Sandra'). Maximum proliferation was achieved with petals on Murashige and Skoog medium supplemented with 0.05 μm TDZ and 0.5 μm NAA. Shoot initiation originated from cells near vascular regions and perhaps from epidermal cells in petals and via organogenic callus from other explants. There was no evidence of chimeral separation from petals or callus, but somaclonal variants (3.3%) were observed involving petal hue and plant dwarfness. Unstable color patterns were observed in tissue-cultured regenerants of `Scania' and `Improved White Sire' similar in type and frequency to propagules derived from cuttings; none were observed for tissue-cultured or cutting-derived plants of `Sandra'. Chemical names used: N-pheny1-N′-l,2,3 -thiadiazol-5-ylurea [thidiazuron (TDZ)]; 1-napthaleneacetic acid (NM).

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X. Cao and F. Hammerschlag

As part of a program to develop transgenic highbush blueberry (Vaccinium corymbosum L.) cultivars, studies were conducted to determine optimum conditions for high-efficiency shoot regeneration from leaf explants of in vitro propagated, commercially important, tissue culture-recalcitrant `Bluecrop' shoot cultures. The effects of pretreatments, growth regulators, and age of explant source on shoot organogenesis were investigated. A maximum of 98% shoot regeneration and 10 shoots regenerating per leaf explant occurred when explants of 2-week-old shoot cultures were incubated in the dark (for a total of 14 days) on pretreatment medium #1 containing 2.6 μM NAA and 5 μM TDZ for 4 days, next on pretreatment medium #2 containing 2.6 μM NAA and 7 μM zeatin riboside for 3 days, then on regeneration medium containing 1 μM TDZ for 6 weeks, and last on medium without growth regulators for 10 days. No shoot regeneration occurred if explants were incubated without exposure to pretreatments before incubation on regeneration medium. There were no significant differences in percentage of regeneration or the number of shoots regenerating per explant from leaf explants derived from either 1-, 2-, or 3-week-old shoot cultures. Shoot production per explant on 1 μM TDZ was about three times that on either 0.5 μM TDZ or 20 μM zeatin riboside, and nine times that on 5 μM TDZ.

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Don Waneck, H. Mathews, J. Stamp, and R. Bestwick

Zygotic embryo explants of grape cultivar AXR#1 were isolated from maw-e seeds and cultured on medium supplemented with naphthoxy acetic acid beta-(NOA) and benzylaminopurine (BA). Embryo explants dedifferentiated to form embryogenic callus. Globular stage embryos were visible in 9-10 months. On transfer 10 a growth regulator free medium supplemented with charcoal these globular embryos underwent further stages of embryo development. In a period of 30-40 days embryogenic tissues turned into clumps of somatic embryos displaying different stages of development Cotyledonary stage embryos were separated and transferred to basal medium. These embryos developed into complete plants. Cold and desiccation treatment of somatic embryos significantly enhanced the rate of plant conversion. Hypocotyl segments of elongated somatic embryos were good source explant for induction of shoot organogenesis. The hypocotyl-length and the proximity to-shoot-apex were found to influence the rate of shoot induction from hypotyl segments. Multiple shoot complexes which formed on hypocotyl segments were separated and individual shoots were grown on a root induction medium resulting in complete plant development. The possibility of both embryogenic and organogenic modes of plant regeneration make somatic embryos a highly versatile explant source for experiments on genetic manipulation.