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Some factors that affect the in vitro conservation of wild pear (Pyrus syrica) microshoot cultures were studied. Sorbitol and mannitol at 0.2 to 4.0 M reduced growth significantly and extended the subculture intervals to 5 months when cultures where kept at 15°C. Increasing sucrose to 12% in the medium was not highly effective and the subculture intervals did not exceed 3.0 months. After 2 years of maintaining cultures on slow-growth medium, cultures grew slowly when transferred to fresh control medium. Shoots started to proliferate after three subcultures (6.0 weeks apart) on medium containing 1.0 mg/L BA and 0.1 mg/L NAA. New microshoots were rooted on medium containing 2.0 mg/L IBA and rooted microshoots gave 90% survival when acclimatized ex vitro under intermittent mist.

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Idaho's population of Pacific dogwood (Cornus nuttallii Audubon) has declined. Propagation of disease-resistant clones would be useful to horticulturists and conservation biologists. In vitro-derived microshoots, incubated for 1 month on woody plant medium supplemented with 6.04 mm calcium gluconate and 4.44 μm benzyladenine, produced an average of 3.1 axillary microshoots per explant. Up to 62% of the elongated microshoots had rooted ex vitro 5 weeks following a 4.5%IBA talc dip. Plantlets resumed shoot growth within 2 months of acclimatization, and 70% survived after 1 year. This protocol is more rapid and efficient than propagation by layering or rooting the difficult-to-root stem cuttings of this species. Chemical names used: 2,3,4,5,6-pentahydroxy-caproic acid (calcium gluconate), benzyladenine (BA), 3-indolebutyric acid (IBA).

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Micropropagated plantlets of avocado (Persea americana Mill.) exhibit a very slow rate of growth during the acclimatization phase, possibly because mycorrhizae are absent. Inoculation of plantlets with the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatum (Thaxter sensu Gerd) Gerd and Trappe improved formation of a well-developed root system that was converted into a mycorrhizal system. Introduction of the mycorrhizal fungus at the time plantlets were transferred from axenic conditions to ex vitro conditions improved shoot and root growth; enhanced the shoot: root ratio; increased the concentration and/or content of N, P, and K in plant tissues; and helped plants to tolerate environmental stress at transplanting. Inclusion of soil as a component of the potting medium appeared to favor mycorrhiza formation and effectiveness. Thus, mycorrhiza formation seems to be the key factor for subsequent growth and development of micropropagated plants of avocado.

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Somatic embryogenesis was induced from internodal callus of `Scania', `Improved White Sim', and `Sandra' carnation (Dianthus caryophyllus L.). The optimum protocol for the induction of somatic embryogenesis included initiation of callus in liquid basal Murashige and Skoog medium supplemented with 3.0 μm 2,4-D followed by transfer to liquid basal medium lacking 2,4-D for embryo development. Somatic embryos originated from single cells and early embryonic development proceeded conventionally (i.e., via globular, heart-shaped, and torpedo stages), but clearly developed apical or root meristems were not always formed. A few embryos developed into seedlings and were acclimatized to ex vitro conditions. Chemical name used: 2,4-dichlorophenoxyacetic acid (2,4-D).

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Three-dimensional polypropylene enclosures have been fabricated for the in vitro culture and ex vitro growth of Cattleya orchid propagules. The enclosures consist of: 1) microporous polypropylene membrane for nutrient transfer between liquid media and the growing tissue. 2) molded polypropylene side wall sized for growth of Cattleya orchid plants and flanged to allow heat seals with membranes, and 3) polypropylene membrane(s) top member for light and gaseous transmission. Three commercial clones of Cattleya have been sealed into these enclosures and grown for eight months on unmended MS medium. Contaminated liquid media was effectively isolated from the propagules within the sealed enclosures, and following a bleach treatment with sterile rinses, propagules were returned to aseptic culture. Greenhouse growth of plant tissues in these enclosures will be discussed. Optimization for growth of Cattleya has begun with studies of gas, light and temperature regimes within the sealed enclosures and a comparison of growth on two different nutrient formulations.

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Shoots of greenhouse-grown Pothos were surface disinfested and explanted on modified Murashige and Skoog (MS) medium. Later they were treated with pulsed XeCl excimer laser radiation for 30 sec. Cultures treated with 12 or 25 pulses of excimer laser radiation showed only 23% and 10% contamination, respectively, versus 75% control. Inaddition, we demonstrated that pulsed XeCl excimer laser radiation affected the subsequent growth and regenerability of in vitro plants. The reason for this increased growth needs further investigation. Both BA and TDZ were important for increasing the number of shoots generated from a microshoot as well as inducing shoot organogenesis from Pothos callus. Of the 50 rooted ex vitro plants from this experiment only 30% were variegated like parental clone. The others were either pure green or albino, suggesting chimeral segregation.

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Shoots of greenhouse-grown Algerian ivy (Hedera canariensis L.) were surface disinfected and explanted on modified Murashige and Skoog (MS) medium supplemented with BA (10 μm) and NAA (2.5 μm). One month later the shoots were transferred to MS proliferation medium supplemented with TDZ (0.1 or 0.5 μm) and NAA (40 μm). An average of three microshoots developed on each stem treated with TDZ. Pruned shoots grown on MS medium supplemented with GA3 (20 μm) and BA (20 μm) branched better than unpruned shoots (3.7 vs. 1 per explant, respectively). Rooted shoots grown ex vitro grew and developed a shape suitable for commercial sale in 3 months. Chemical names used: N -(phenyl-methyl)-l H -purine-6-amine (BA); gibberellic acid (GA3); 1-naphthaleneacetic acid (NM); N -phenyl-W-1,2,3-thiadiazo-5-yl urea (Thidiazuron, TDZ).

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Minituber production was investigated using ex vitro `Norland' plantlets in a rockwool-based hydroponic system. Productivity was evaluated for 12- and 16-h photoperiod pre-treatment, planting density (two, four, and six plantlets/slab), vertical or horizontal orientation, pinching, and hilling. Total yield differences did not result from photoperiod pre-treatments, but 12-h pre-treatment increased the number of minitubers in the desirable 10- to 40-g size range. Increased planting density reduced yield per plant but caused small increases in yield per slab. Planting orientation, pinching, or hilling had no effect on overall fresh weight yield, number, or size distribution. Short photoperiod pre-treatment, and planting densities of four to six plantlets/slab, oriented vertically, are recommended.

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Traditional seed propagation (warm/cold stratification) was compared to embryo culture of Chionanthus virginicus L. to determine if germination could be promoted and time necessary to produce a sizable plant could be reduced. Embryos of C. virginicus were extracted from immature fruit collected 9, 16, and 23 Aug. 1995 and grown in vitro on Anderson's rhododendron medium. They germinated in 4 weeks and were transferred ex vitro to flats. Mature fruit from the same source were grown simultaneously using warm/cold stratification. The two groups were evaluated periodically over a 2-year period for percent germination, plant size, and seedling success. The embryo-cultured plants had a lower survival rate (16% vs. 44%) and were more labor intensive. After 2 years, embryo-cultured plants were 13.4-fold the mass and 4.7-fold taller than traditionally grown plants. Ten-month-old cultured plants were comparable in size to 2-year-old plants grown traditionally.

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A micropropagation system was developed for hazelnut cultivars. Grafted greenhouse-grown plants produced many more viable explants than upper branches of mature field-grown trees. Shoots from grafted greenhouse-grown plants collected March through July and suckers of mature field-grown trees collected in July produced the most growing explants (46% to 80%). Three- to five-fold multiplication was obtained after 4 weeks of culture on NCGR-COR medium supplemented with 6.7 μm BA and 0.04 μm IBA. Roots were produced on 64% to 100% of shoots grown on half-strength NCGR-COR mineral salts and 4.9 μm IBA for 4 weeks. Ex vitro rooting by a brief dip in 1 or 5 mm IBA was equally successful. Transplant survival was 78% to 100%. Chemical names used: N 6-benzyladenine (BA); indole-3-butyric acid (IBA).

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