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A. M. Richwine, J. Tipton, and G. Thompson

Hesperaloe parviflora is a useful xeric landscape plant. Two methods of shoot culture initiation were developed. Shoots were initiated indirectly through the use of callus derived from pieces of young inflorescences. Callus was initiated on modified Murashige and Skoog medium with 4.52 μM 2,4-dichlorophenoxyacetic acid and 2.32 μM kinetin. Callus produced shoots when placed on modified MS medium with 6.0 μM zeatin riboside. Direct initiation of shoots was also accomplished using the bottom four floral buds of young inflorescences. Buds were placed on modified MS media containing either benzylaminopurine or kinetin at 0.1, 1.0, or 10.0 μM or zeatin riboside at 6.0 μM. The most shoots were produced by the medium containing 6.0 μM zeatin riboside. Preliminary results indicate optimum shoot production with 2.0 to 4.0 μM BA or 6.0 μM zeatin riboside.Hesperaloe parviflora micro-shoots were rooted on one quarter strength MS medium and ex vitro.

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Dennis P. Stimart and John C. Mather

Cotyledons from developing embryos 6 to 8 weeks old of Liatris spicata (blazing star) were cultured on Murashige-Skoog (MS) medium containing 0, 0.4, 4.4, and 44.4 μ M benzyladenine (BA) or 0, 0.2, 2.2, and 22.2 μ M thidiazuron (TDZ) to induce adventitious shoot formation. The highest percent of cotyledons forming shoots with highest shoot counts was on medium containing 2.2 μ M TDZ. Vitreous shoots formed on medium with 22.2 μ M TDZ. Callus derived from cotyledons and cultured on medium containing 4.44 μ M BA or 2.2 μ M TDZ formed adventitious shoots with highest shoot counts on 4.44 μ M BA. Adventitious shoots derived from cotyledons and callus were rooted on MS medium with 5.0 μ Mindole-3-butyric acid, acclimatized and grown ex vitro. All micropropagated plants appeared similar to each other.

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Richard K. Kiyomoto and Mark H. Brand

Experiments were conducted on tissue proliferation (TP) development and in vitro and ex vitro growth of tissues from plants with (TP+) and without TP (TP-). In 1993 the increase in TP in one-, two-, and three-yr-old `Holden' and `Besse Howells' was 3%, 52%. and 32% and 10%, 26% and 21%, respectively. No differential mortality was observed. Shoot tip cultures initated from TP+ and TP- `Montego' showed 10-12 mo were required for miniaturiziation and multiplication in TP- shoot tips and 4 mo in TP+ shoot tips. TP- cultures require 10 uM 2-iP for normal shoot proliferation; whereas TP+ cultures had to be transferred to hormone-free medium after 6 mo to maintain normal shoot morphology. Cutting propagation from TP- and TP+ plants older than 5 yr, showed persistence of morphological aberrations associated with TP+ plants.

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M.T. Vidal, C. Azcón-Aguilar, J.M. Barea, and F. Pliego-Alfaro

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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Xiaoling Yu and Barbara M. Reed

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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Fouad Mohamed, Harry Jan Swartz, and George Buta

In previous abstracts (HortScience 23:707;24:121), ABA when added throughout the in vitro production cycle, reversed the tissue culture-induced rejuvenation of the day neutral strawberry `Fern'. Compared to benzyl adenine (BA) proliferated plants, ABA treated tissue culture-produced plants flowered earlier and had more adult leaf patterns. In the present study, we analysed endogenous ABA concentrations in the apices and unexpanded leaves of BA treated tissue culture-propagated plants, selved seedlings and propagated adult runner tip plants at 3, 7 and 15 weeks ex vitro, after germination or after runner tip propagation. Using pentadeuterated standards and single ion monitoring, ABA concentrations in tissue culture produced and juvenile seedling plants were significantly lower than adult plants at 3 and 7 weeks. By 7 weeks, only the adult plants were flowering. At 15 weeks, no differences in ABA concentration were significant and all three types flowered.

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José M. Iriondo, Carmen Moreno, and César Pérez

Micropropagation methods for six rockrose species (Cistus albidus L., C. clusii Dunal, C. ladanifer L., C. laurifolius L., C. psilosepalus L., and C. salvifolius L.) were established. Cultures, initiated from nodal segments of seedlings, were grown on MS medium, alone, or supplemented with 0.88 μm BAP or 0.93 μm Kin. Multiple shoot formation was obtained after the first subculture (30 days) from which new nodal segments were taken and grown on the same culture medium to maintain proliferation. Shoots obtained at the third subculture were rooted alone or supplemented with different concentrations of IBA. The plantlets of the six species, thereby obtained, were successfully acclimatized to ex vitro conditions. Chemical names used: 6-benzylaminopurine (BAP), indole-3-butyric acid (IBA), 6-furfurylaminopurine (Kin).

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R. Lowe and D. Donnelly

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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Charlotte R. Chan and Robert D. Marquard

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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Rida A. Shibli, M. Ajlouni, A. Jaradat, and M. Shatnawi

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.