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  • Author or Editor: Paul E. Read x
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Abstract

Dipping the basal inch of cuttings in 2500 ppm succinic acid 2,2-dimethylhydiazide (SADH) solutions for 15 sec promoted rooting of carnation (Dianthus caryophyllus L.) and poinsettia (Euphorbia pulcherrima Wild). Materials such as (2-chlorethyl)trimethylammonium chloride (chlormequat), N-pyrrolidino-succinamic acid (SAPL), gibberellic acid (GA), abscisic acid (ABA), 2-chloroethylphosphonic acid (ethephon) and ethylhydrogen 1-propylphosphonate (EHPP) either decreased or had little effect on rooting.

Open Access

Seeds from three phenotypes of Yucca glauca were germinated using two pre-germination treatments for each phenotype. Treatments were: a 10% NaOCl (10 NaOCl) soak for 15 minutes and a 50% NaOCl (50 NaOCl) soak for 24 hours. Seeds were then placed on Linsmaier-Skoog (LS) medium in darkness for two weeks at 27-28 C. All radicles were emerging through the seed coats at the end of 50 NaOCl as compared to no visual difference in the seed appearance after 10 NaOCl. At the end of the two incubation periods, seeds from 50 NaOCl exhibited shoot development and elongation while seeds from 10 NaOCl exhibited little or no shoot development or elongation. Seeds from 10 NaOCl exhibited contamination and/or “bleeding” (phenolic exudates) within 4 weeks. All seedlings were transferred to fresh LS medium and cultured for 6, 12 and 18 weeks. Seedlings that received the 50 NaOCl developed fibrous roots at 8-10 weeks and the beginnings of a tap root at 16-20 weeks. Ten seedlings from 50 NaOCl were transplanted 9 months after germination.

Free access

Juvenile Yucca glauca plants, with a fibrous, woody rhizomatous root still connected to the mother plant and well developed basal fibrous roots that were present when they were transplanted prior to tap root development, exhibited faster recovery from transplant stress and earlier bloom as compared with juvenile plants transplanted with fully developed immature taproots. All juvenile transplants exhibited >90% survival as compared with mature transplants with fully developed taproots, none of which survived. Juvenile transplants with no taproot development prior to transplanting recovered and produced flower stalks with full bloom within 2 years of transplanting. Juvenile transplants with taproot development took 3 years from transplant to recover and produced flower stalks with full bloom.

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Authors: and

Ethanol has been used as a disinfestation agent for in vitro studies and micropropagation purposes. A previous study indicated that ethanol may have effects similar to those of bleach solution on bud break of woody species (Yang and Read, 1992). Research was therefore conducted to determine ethanol effects on the breaking of bud dormancy. The basal one third of dormant lilac, privet and spirea stems was soaked in different concentrations of ethanol solution (0, 25, 50, 75 or 95%) for 15 minutes before placement in the forcing solution. The results demonstrated that the pre-forcing ethanol treatments hastened bud break for lilac and privet while delaying bud break for spirea. The percentage of bud break and shoot elongation for lilac and privet were also promoted. Generally speaking, 75% ethanol was the best treatment. Quality softwood growth was therefore produced in the off-season. Such new growth can then be used either as explant materials for micropropagation or as cuttings for rooting.

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Authors: and

Plant growth regulators (PGR) in the forcing solution have been demonstrated to influence the bud break and shoot elongation for a wide range of woody plant species (Yang and Read, 1989). However, it was not clear how PGR in the forcing solution modified the breaking of bud dormancy at the molecular level, in terms of protein expression. Dormant stems of spirea and privet were forced in forcing solution containing 200 mg 8-hydroxyquinoline citrate per liter and 2% sucrose, plus different concentrations of BA, IBA or GA 3 . New softwood growth was harvested for protein analysis. The preliminary results suggest that total protein expression was stimulated by adding BA or GA 3 to the forcing solution for spirea and privet. The protein expression was not well correlated with the concentration of IBA in the forcing solution. However, a slight increase of total protein expression was noticed when a higher concentration of IBA was added to the forcing solution for privet. Results of this research will be discussed in relation to development of a better understanding of the physiology of bud dormancy.

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Native plants are often ignored in horticulture because they may lack major ornamental traits and many of them are difficult to propagate. Creamy indigo (Baptisia bracteata Mnhl.) is a North American legume with considerable potential as a container-grown or ornamental plant for managed landscapes. Nodal explants from aseptically germinated seedlings were evaluated for axilary shoot and leaf development. The explants were cultured on Murashige and Skoog medium (MS) containing adenine sulfate at 80 mg•L-1, 30% sucrose, and different levels of N-6-benzyladenine (BA) (0.5,1.0,2.0 mg•L-1) supplemented with indole-3-acetic acid (IAA) (0.05, 0.1 or 0.5 mg•L-1) or with IAA omitted. Shoot regeneration occurred within 2 to 3 weeks. The best medium for shoot regeneration was MS supplemented with BA at 1.0 mg and IAA at 0.1 mg•L-1. Shoots were transferred onto rooting medium consisting of Ω MS supplemented with 1.0 mg alpha-naphthaleneacetic acid (NAA) and 1.0 mg indole-3-butyric acid (IBA)/L and 20% sucrose. Rooting took place within 3 to 5 weeks. Plantlets were then planted in soil mix, placed under a polyethylene tent for 2 weeks, and transferred into the greenhouse for further growth.

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American chestnut (Castanea dentata) is one of the United States' most valuable resources for its nuts and timber. Many scientists are exploring genetic transformation techniques to improve chestnut blight resistance in addition to conventional breeding. In vitro shoot production must be first obtained and optimized in order to establish an efficient transformation system. Although shoot proliferation has been achieved, chestnut is still considered difficult for tissue culture with poor rooting. Therefore, this research has focused on improving rooting ability of micropropagated chestnut shoots. In vitro shoot production was established and maintained in WPM supplemented with 0.1 mg/l BA, 3% sucrose, and 0.7% agar with the pH adjusted to 5.8. The shoots were then transferred to rooting medium containing the same components as for shoot proliferation plus an auxin at various concentrations. Right after placing shoots onto rooting medium, a very thin layer (5 ml) of the same auxin (diluted) was added to provide a quick stimulation of rooting. Detailed discussion will be presented.

Free access

The American Chestnut Foundation (ACF) has conducted a breeding program aimed at developing blight-resistant chestnut trees exhibiting the phenotype of American Chestnut (Castanea dentata). We developed a protocol for in vitro micropropagation and multiplication of candidate blight-resistant plants from the ACF breeding program. The protocol included forcing dormant shoots to budbreak, culture establishment, shoot multiplication, inducing a functional root system on the microcuttings produced by this system and establishment of autotrophic plants. Because Castanea spp. is recalcitrant to rooting, a unique bilayer method of rooting was developed. The unique bilayer consisted of a clear basal medium of 50% DKW and 50% WPM (Long and Preece), with a continuous level of 0.01 mg IBA/L and 0.2 mg BA/L. The clear basal medium was over-laid with an opaque layer. Rooting response occurred for 27 of the 31 genotypes at various frequencies. Rooted plantlets were planted in 50% peat: 50% perlite in order to become autotrophic and acclimated. Acclimated trees were planted in 10″ × 2″ Deepots® and placed in the greenhouse. These trees exhibited a very vigorous functional root system. Acclimated trees were hardened off, placed in cold storage (≈4-5 °C) for 5 months. All trees placed in cold storage broke dormancy for spring growth and ≈100 trees were sent to ACF for planting into field trials.

Free access

Abstract

Shoot tips of azalea (Rhododendron spp.) accessions 620014, 800057, and 800374 multiplied rapidly when cultured on a Murashige and Skoog (MS) medium modified by reducing concentrations of NH4NO3 and KNO3, adding (NH4)2SO4 (to give an NH 4 + : NO 3 ratio of 1:1), omitting KI, and replacing Na2EDTA and FeSO4 with FeNaDTPA. The organic constituents were in mg/liter: thiamine-HCl, 0.4; myo-inositol, 100; sucrose, 20,000; agar, 6,000; N6-(Δ2-isopentenyl)-adenine (2iP), 5, 10, or 20 and the pH varied from 4.0 to 6.0 with 5.0 the most effective. An average 4-to-6-fold multiplication rate for the different clones was achieved after 10 weeks culture in this medium and weekly subculturing was unnecessary and detrimental. The harvested shoots could be rooted either in a soilless medium or recultured on fresh medium. The tissue remaining after shoot harvest, when recultured on fresh medium, produced 11–34 shoots for additional harvests at 6-week intervals. Additions of 1 mg/liter indoleacetic acid (IAA) in the medium in such recultures increased the number of usable shoots and improved their quality.

Open Access

Abstract

Differences were observed in microcutting harvests from 5 shoot tip explant sequential recultures of the hardy deciduous azalea (Rhododendron spp.) accessions 800374, 620014, and 800057. In general microcutting production increased and then declined over reculture times in a nearly bell-shaped curve for all 3 clones tested. Maximum numbers of usable microcuttings were harvested in the 3rd and 4th recultures. Productivity varied among the 3 clones, with accession 800374 the most prolific and accession 800057 the least. The microcutting height was the same for all 5 recultures of accessions 800374 and 620014, whereas, in accession 800057 the height declined from the 1st through the 5th reculture. The microcutting quality rating was similar throughout all recultures of accessions 800374 and 620014, but accession 800057 produced higher quality microcuttings in the 3rd reculture than in the 5th reculture. Rooting of microcuttings in soilless medium increased from the 1st to the 5th reculture for all 3 clones, reaching more than 97% for the last 2 harvests.

Open Access