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I. Arrillaga and S.A. Merkle

A protocol to achieve efficient plant regeneration from juvenile black locust (Robinia pseudoacacia L.) explants is described. Direct adventitious shoots were induced from cotyledon explants on woody plant medium containing 22.2 μm BA and 0.4 μm 2,4-D. Shoots developed and new shoots were induced when the explants were transferred to medium without growth regulators. The effect of dark incubation on shoot regeneration from cotyledons indicated that 15 days of darkness resulted in a high regeneration frequency (91.7%). Adventitious shoot formation also was induced from sections of in vitro-derived leaves cultured in darkness on Murashige and Skoog medium supplemented with 4.4 μm BA and 24.6 μm IBA. A shoot regeneration frequency of 89% was obtained when explants were subcultured on a medium containing 4.4 μm BA and 0.5 μm IAA. Shoots were rooted on Schenk and Hildebrandt medium with or without IBA. Plantlets were acclimatized and grown in the greenhouse. Chemical names used: N -(phenylmethyl)-1H -purin-6-amine (BA); 2,4-dichlorophenoxyacetic acid (2,4-D); indole-3-acetic acid (IAA); indole-3-butyric acid (IBA).

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Dennis P. Stimart and John C. Mather

Cotyledons from developing 6- to 8-week-old embryos of Liatris spicata (L.) Willd. (blazing star) were cultured on Murashige and Skoog medium containing 0, 0.4, 4.4, or 44.4 μm BA or 0, 0.2, 2.2, or 22.2 μm TDZ to induce adventitious shoot formation. The highest percentage of cotyledons forming the most shoots was on medium containing 2.2 μm TDZ. Cotyledon-derived callus cultured on medium containing 4.4 μm BA formed ≈16 times more adventitious shoots than on 2.2 μm TDZ. Adventitious shoots derived from cotyledons or callus produced roots when placed on MS medium containing 5.0 μm IBA. Regenerated plants that flowered in the field appeared homogeneous. Chemical names used: N6-benzyladenine (BA), thidiazuron (TDZ), indole-3-butyric acid (IBA).

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Enio Tiago de Oliveira, Otto Jesu Crocomo, Tatiana Bistaco Farinha, and Luiz Antônio Gallo

A protocol for large-scale Aloe vera (L.) Burm. f. production was established using micropropagation of apical buds. The effects of two chlorine-based disinfectants were evaluated on the survival of the explants in different treatments in a semisolidified Murashige and Skoog (MS) medium in the presence of 6-benzylaminopurine (6-BAP; 2 mg·L−1). During 120 days, 136 green apical shoots bearing axillary buds were multiplied four times at 30-day intervals in the same MS medium, reinoculating seven to nine explants per flask each time. The elongation and rooting processes were carried out in the same MS medium without 6-BAP. A total of 40,495 Aloe vera microplants were obtained, a yield of 300 microplants per apical bud at a rate of 1:5.3 in every multiplication period of 30 days. From that total, 38,480 Aloe vera microplants were successfully acclimatized transferring to 36- and 64-cell polyethylene trays containing proper substrate in two different ex vitro greenhouse conditions. After a 3-month period, fresh and dry matter weights of the Aloe vera plants were determined. All the data from each experimental phase were statistically analyzed. The use of 64-cell (40 cm3/cell) trays represented an economy of 47.37% in greenhouse space and 50% in the amount of substrate per Aloe vera plant.

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Ana Carolina Espinosa, Paula M. Pijut, and Charles H. Michler

A complete regeneration protocol was developed for Prunus serotina Ehrh., an important hardwood species for timber and sawlog production in the central and eastern United States. Nodal sections were cultured on Murashige and Skoog (MS) medium supplemented with 4.44 μm 6-benzylaminopurine (BA), 0.49 μm indole-3-butyric acid (IBA), and 0.29 μm gibberellic acid (GA3). In vitro leaf explants of three genotypes were placed on woody plant medium (WPM) supplemented with 0, 2.27, 4.54, or 6.81 μm thidiazuron (TDZ) in combination with 0, 0.54, 1.07, or 5.37 μm naphthaleneacetic acid (NAA), and on WPM supplemented with 0, 4.44, 8.88, or 13.32 μm BA in combination with 0, 0.54, 1.07, or 5.37 μm NAA. Cultures were maintained either in continuous darkness for 5 weeks, or in the dark for 3 weeks and then transferred to a 16-hour photoperiod. TDZ and the genotype had a significant effect on the number of shoots regenerated. The maximum mean number of shoots regenerated per explant (5.05 ± 1.14) was obtained with 2.27 μm TDZ plus 0.54 μm NAA with the 3-week dark period then light treatment. The highest percent shoot regeneration (38.3) and mean number of shoots (4.13 ± 0.97) was obtained with 6.81 μm TDZ plus 1.07 μm NAA. The highest rooting (27%) of adventitious shoots and number of roots per shoot (2.3 ± 0.2) was obtained with 2.5 μm IBA when shoots were maintained for 7 days in the dark on rooting medium before transfer to a 16-hour photoperiod. The highest rooting (70%) of nodal explant-derived stock cultures and number of roots per shoot (2.7 ± 0.9) was also obtained with 2.5 μm IBA, but when shoots were maintained for 4 days in the dark before transfer to a 16-hour photoperiod. In total, 86% of the plantlets survived acclimatization to the greenhouse and 100% survival after overwintering in cold-storage.

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James A. Kapaun and Zong-Ming Cheng

Plants were regenerated from leaf tissue of greenhouse-grown seedlings of Siberian elm (Ulmus pumila L.). Shoot regeneration was induced on Murashige and Skoog (MS) medium containing 5 to 10 μm of BA. Up to 55% of the leaf explants formed shoots with an average of 2.4 shoots per explant. Addition of 2.5 or 5 μm of IBA failed to enhance regeneration. Thidiazuron at 0.5 or 1.0 μm also induced shoot regeneration, but the shoots failed to elongate as well as shoots regenerated from media containing BA. Incubation in darkness for 7, 14, or 21 d had little effect in promoting shoot regeneration, except that incubation for 21 d increased shoot regeneration on the medium with 5.0 μm BA. Genotypes differed in shoot regeneration potential, with regeneration frequencies ranging from 13% to 55%. Regenerated shoots were micropropagated on Driver and Kuniyuki Walnut medium. Ninety percent of microcuttings rooted directly in potting soil. This regeneration system will be valuable for genetic transformation and cell selection of Siberian elm. Chemical names used: 6-benzylaminopurine (BA); indole-3-butyric acid (IBA); N-phenyl-N′ -1,2,3-thiadiazol-5-ylurea (thidiazuron, TDZ).

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Chiu-Yueh Hung and Jiahua Xie

A method of in vitro plant regeneration for both the selenium-hyperaccumulator Astragalus racemosus ‘Cream Milkvetch’ and the nonaccumulator Astragalus canadensis ‘Canadian Milkvetch’ was developed with two induction media, M1 and M2. The M1 and M2 contain Murashige and Skoog basal medium plus vitamins, 8.07 μm N-(2-chloro-4-pyridyl)-N′-phenylurea, 2.5% (w·v−1) sucrose, 0.7% (w·v−1) agar (pH 5.7), and 0.89 μm or 3.12 μm a-naphthaleneacetic acid, respectively. In vitro cultures were initiated on these two types of media with three types of explants: cotyledons, hypocotyls, and roots. More than 93% of cultured explants from both species could form calli or calli with shoots. With regard to shoot formation, A. canadensis could produce multiple shoots from all types of explants more efficiently than A. racemosus. The highest shoot induction was approximately three shoots per explant in A. racemosus, whereas A. canadensis could reach ≈10 shoots per explant. M1 could induce more shoots than M2 no matter what type of explant was used, but the overall induction rates were no significant difference. Among the three types of explants used, the cotyledons were the best explants for shoot induction in A. canadensis, whereas hypocotyls were the best in A. racemosus. In A. racemosus, shoots could also be obtained from calli on the rooting medium containing Murashige and Skoog basal plus vitamins, 2.84 μm indole-3 acetic acid, 2.5% (w·v−1) sucrose, and 0.7% (w·v−1) agar (pH 5.7). Approximately 43% of A. canadensis shoots and 19% of A. racemosus shoots could be rooted on the rooting medium.

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Yuexin Wang, Zoran Jeknić, Richard C. Ernst, and Tony H.H. Chen

To improve the efficiency of iris plant regeneration, we tested the influence of several combinations of Kin and NAA in culture media on the induction of morphogenesis and the subsequent development of plantlets. The highest rates of regeneration (67%) were consistently observed in induction media containing 0.5 μm NAA and either 2.5 or 12.5 μm Kin. Developing medium containing 1.25 μm BA was optimal for high regeneration rates and a high percentage of plantlets simultaneously developing shoots and roots. Rooted plantlets were easily acclimatized and transplanted to various soil mixtures, then grown in the greenhouse. Under optimal conditions as many as 8000 plantlets could be regenerated from 1 g of cells in ≈4 months. Chemical names used: kinetin (Kin); 1-naphthaleneacetic acid (NAA); N6-benzyladenine (BA).

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Robert L. Geneve, Wesley P. Hackett, and Bert T. Swanson

Exogenous ethylene could not substitute for NAA to induce adventitious root initiation in juvenile petiole explants of English ivy (Hedera helix L.), indicating that the action of auxin-stimulated root initiation was not directly mediated through ethylene production. Mature petioles did not initiate roots under any auxin or ethylene treatment combination. Ethephon or ACC supplied at 50 or 100 μm was inhibitory to NAA-induced root initiation in juvenile petioles. The pattern of ethylene production stimulated by NAA application was significantly different in juvenile and mature petioles. Ethylene evolution by juvenile petioles declined to near control levels during from 6 to 12 days after NAA application. Reduction in ethylene production was due to reduced availability of ACC in juvenile petioles. Mature petioles continued to produce ethylene at elevated levels throughout the course of the experiment. Ethylene does not appear to play a significant role in the differential root initiation response of juvenile and mature petioles treated with NAA. However, ethylene appeared to have an inhibitory effect during root elongation stages of adventitious root development in juvenile petioles. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); 1-napthaleneacetic acid (NAA); 2-chloroethylphosphonic acid (ethephon).

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Gerson R. de L. Fortes and Silvio L. Teixeira

The aim of this work was to study different apple of somatic material as callus and adventitious shoots are concerned, for further utilization in the research of somaclonal variation. The somatic materials were: leaf discs, cotyledons and hypocotyls of Gala apple seedlings, cultivated in a MS medium added by B5 vitamins in addition to (in mg/l): BAP (1,0), NAA (0,5) mio-inositol (100,0) sucrose (30,0 g/l) and solidified in agar (6,0 g/l). The several times of explant exposition to the dark affected the final callus weight. Callus weight derived from leaf discs were higher than those for cotyledons and hypocotyls. Explants exposed directly under light or up to two weeks in the dark showed less percentage of regenerative callus as compared to those of three weeks in the dark. The leaf explants presented the highest percentage of regenerative callus. The least response was obtained for those derived from hypocotyls. The highest number of adventitious shoots was obtained keeping the explants three weeks in the dark as compared to directed light exposition.

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Mohamed F. Mohamed, Paul E. Read, and Dermot P. Coyne

Dry seeds from two lines of common bean (Phaseolus vulgaris L.) and one cultivar of faba bean (Vicia faba L.) were germinated on Murashige and Skoog (MS) medium containing B vitamins, 30 g sucrose/liter, and either 2.5, 5.0, or 7.5 μm benzyladenine (BA). Axenic seed cultures were grown at 22 to 24C in darkness and under continuous light from cool-white fluorescent tubes (40 μmol·m-2·s-1). Explant tissues were prepared from cotyledonary nodes (CN) and primary nodes (PN) of 14-day-old seedlings. Explants were cultured on corresponding seedling growth medium and maintained under continuous cool-white light (40 μmol·m-2·s-1). The percentages of CN and PN (in one line of common bean) explants that regenerated shoots and the number of shoots per explant (in all germplasm) were highest when nodal tissues were prepared from seedlings germinated in darkness. These responses were optimal on medium containing 5 μm BA during seedling growth and subsequent culture of explants. The number of shoots per explant was two to five times higher on explants cultured on medium with 0.25 to 1.0 μm forchlorfenuron (CPPU) or thidiazuron (TDZ) than on medium with 5 μm BA. Higher (2.5 and 5 μm) CPPU and TDZ concentrations inhibited shoot elongation and stimulated callus production. Histological analyses indicated that adventitious meristems formed 6 to 8 days after explant culture. Progenies from regenerated plants appeared similar to plants raised from the original seed stocks. Chemical names used: N- (phenylmethyl) -1 H- purin-6-amine (benzyladenine, BA); N- (2-chloro-4-pyridyl)-N'- phenylurea (forchlorfenuron, CPPU); N- phenyl -N' -1,2,3-thiadiazol-5-ylurea (thidiazuron, TDZ).