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Takuya Tetsumura and Hisajiro Yukinaga

Microshoots of Japanese persimmon (Diospyros kaki L. cv. Jiro) were rooted in vitro. The roots were excised and cultured on solidified Murashige and Skoog medium. After 20 days of culture, adventitious shoots formed spontaneously and directly from the roots. Of all the tested cytokinins, 10–5 m zeatin in combination with 10–8 m IAA was the most effective in stimulating production of adventitious shoots. CPPU and 2iP also were effective cytokinins. Addition of a high concentration of auxin, especially 2,4-D, to the medium inhibited adventitious shoot formation. The percentage of root segments forming adventitious shoots increased with increasing segment length. Almost all of the longest roots (4 to 6 cm) formed adventitious shoots. Chemical names used: 6-benzyladenine (BA); 2,4-dichlorophenoxyacetic acid (2,4-D); indole-3-acetic acid (IAA); 2-isopentenyladenine (2iP); N-phenyl-N′-(2-chloro-4-pyridyl)urea (CPPU).

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Margarita Fraga, Mertxe Alonso, and Marisé Borja

Meristem culture and/or thermotherapy were used for virus elimination from ornamental Phlox paniculata L. (`Blue Boy', `Orange perfection' and `Starfire') mother plants. Shoot tip, leaf, node and flower ovary explants collected from greenhouse-maintained virus free plants were cultured in vitro for shoot initiation. Adventitious shoot initiation was observed on Murashige and Skoog (MS) medium containing the cytokinin BA with or without the auxin NAA. The addition of 0.4 mg·L-1 thiamine, 0.4 mg·L-1 folic acid, and 40 mg·L-1 adenine sulfate to the MS medium did not improve the regeneration rate. Multiplication and rooting were genotype dependent. Blue Boy and Orange Perfection cultivars regenerated the maximum number of shoots from leaf explants. `Blue Boy' leaf explants from in vitro plants had a lower regeneration rate than explants from greenhouse plants. Cultivar `Starfire' had the highest shoot formation with open flower ovary explants and failed to regenerate from leaf explants. In vitro rooting of adventitious shoots in the presence of auxins (IAA, NAA, or IBA) with or without BA was less effective than ex vitro rooting. Chemical names used: 6-benzyladenine (BA); indole-acetic acid (IAA); indole-3-butyric acid (IBA); α-naphthaleneacetic acid (NAA).

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F.A. Hammerschlag and A.C. Smigocki

Peach [Prunus persica (L.) Batsch] plants #94-1, #99-1, and #40-1, carrying a cytokinin biosynthesis (ipt) gene following transformation with the shooty mutant strain of Agrobacterium tumefaciens, were evaluated for altered growth habit and axillary shoot formation, both in vitro and in the greenhouse. After 9 weeks of in vitro propagation on four different levels of 6-benzyladenine (BA), only transformant #99-1 exhibited significantly greater axillary shoot formation (on 10 μm BA), and significantly greater fresh mass (on 3,10, and 30 μm BA) than the control #RG-3. Tolerance to a supra-optimal (30 μm) concentration of BA was indicated by fresh mass increases for #99-1 shoot cultures. Delayed senescence on 0 μm BA was exhibited by 87% of the transformants, but by only 12% of the control plants. Greenhouse-grown #99-1 and #40-1 were significantly shorter than #RG-3 plants at 6 weeks and at 1 year, but only #40-1 exhibited significantly greater branching than the controls. Chemical names used: 6-benzyladenine (BA); isopentenyl transferase (ipt).

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Ben van Hooijdonk, David Woolley, Ian Warrington, and Stuart Tustin

limits root growth and/or cytokinin biosynthesis and consequently the amount of root-produced cytokinin supplied to the scion in the xylem vasculature. In support of this hypothesis, cytokinins were identified in the xylem sap of apple trees ( Jones, 1973

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W.L. Chen and D.M. Yeh

). Environmentally friendly methods, such as reduced water supply to stock plants, may be an alternative to decrease endogenous pathogens ( Debergh and Maene, 1981 ). Culture media supplemented with cytokinins are crucial for shoot multiplication in aroids

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I.E. Yates and C.C. Reilly

The influence of stage of fruit development and plant growth regulators on somatic embryogenesis and the relation of cultivar response on somatic embryogenesis and subsequent plant development have been investigated in eight cultivars of pecan [Carya illinoensis (Wangenh.) C. Koch]. Explants from the micropylar region of the ovule were more embryogenic when removed from fruits in the liquid endosperm stage than were intact ovules from less-mature fruits or from cotyledonary segments of more-mature fruits. Explants conditioned on medium containing auxin alone or auxin + cytokinin produced more somatic embryos than medium containing cytokinin alone. Under the conditions of this study, frequency of embryogenesis, as well as the germination of somatic embryos leading to plant development, indicated appreciable variation among cultivars. Plant development was greatest by far from somatic embryos of `Schley' than other cultivars studied.

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Bernhard Bessler

Some species of the genus Tillandsia (Bromeliaceae) are highly endangered in their natural habitats. This report introduces a method for induced lateral shoot development in atmospheric Tillandsias using the cytokinin BAP. Spraying or dipping the plants with BAP-solutions induced many lateral shoots. Even difficult-to-propagate species like T. cacticola L.B.SM developed up to 30 times more usable shoots than the control. Applying low concentrations (1 and 5 mg·L-1) over a longer period of time (10 weeks, 3 times a week) produced results similar to those using higher concentrations (50 mg·L-1) for shorter periods (2 weeks, 3 times a week). Chemical name used: 6-benzylaminopurine (BAP).

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Barbara M. Reed and Ana Abdelnour-Esquivel

Explants of mature pot-grown Vaccinium corybosum L. cultivars were tested for initiation of new shoots using two growing conditions and four cytokinin treatments. Initiation tests with 12 genotypes showed significantly higher rates of new shoot growth on modified woody plant (MWPM) medium with 4 mg zeatin/liter at 25C under low light intensity than on any other treatment. Explants at 25C in light with 10 or 15 mg 2iP/liter initiated at a moderate rate, but significantly lower rates were found for all controls and at 4C in darkness. To determine the utility of zeatin for initiation of diverse genotypes, 96 Vaccinium accessions from the National Clonal Germplasm Repository, representing 22 species and 44 cultivars, were screened using 25C and low light intensity. Initiation rates higher than 60% were achieved for 89 of 96 accessions tested. Chemical name used: N6-[2-isopentenyl] adenine (2iP), 6-[4-hydroxy-3-methylbut-2-enylamino]purine (zeatin).

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D.M. Glenn and R. Scorza

In reciprocal grafts of tall (`Elberta' and `Loring') and dwarf (`Empress' and `Juseito') peach (Prunus persica Batsch.) phenotypes, we measured dry-matter partitioning, resistance to root system water flow, and phytohormone content of xylem exudate. Scion characteristics determined the phenotype and growth characteristics of the tree irrespective of the rootstock. Tall phenotypes had higher dry weight and lower root resistance to water flow than dwarf phenotypes. Cytokinin-like activity and auxin levels in xylem sap were higher in dwarf than in tall phenotypes; whereas gibberellin-like activity was unaffected by either rootstock or scion. The scion of peach influenced phytohormone levels and resistance to water flow in the root system in addition to root and shoot growth.

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Maria Papafotiou and Aekaterini N. Martini

studied using explants of different origin (seedlings grown in vitro, mature, native, and greenhouse plants) for culture establishment, testing various cytokinins for shoot growth and proliferation, as well as examining various IBA concentrations and