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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

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.

Free access

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

Abstract

Three Typha species were micropropagated successfully using immature inflorescence segments as the explant. Plantlet production via organogenesis was optimum when the explants were first placed on LS medium + 5.0 mg°liter−1 2,4-D to initiate callus production, and after 9½ weeks the callus was recultured on LS + 1.0 mg°liter−1 benzyladenine (BA). Of three species tested, T. glauca produced callus and new shoots more readily than T. latifolia or T. angustifolia. As inflorescences matured, an increased level of an auxin-like plant growth regulator, picloram, was necessary for callus induction. Excision and separate culture of green “spots” or clumps that formed on the calli enhanced shoot regeneration from the callus. Chemical names used: (2,4-dichorophenoxy)acetic acid (2,4-D) and A-(phenylmethyl)-1H-purin-6-amine (BA).

Open Access

Abstract

Leaf explants from ‘Sugar Daddy’ and ‘Sugar Plum’ petunia (Petunia hybrida L.) were pretreated in solutions of 0, 200, 400, and 800 mg/liter 6-benzylamino purine (BA) and were placed in a cytokinin-free modified Murashige and Skoog (MS) medium, to which 0.05, 0.1, or 0.2 mg/liter naphthaleneacetic acid (NAA) were incorporated to test interaction. NAA at 0.05 or 0.1 mg/liter increased shoot number, fresh weight, and shoot quality rating for ‘Sugar Daddy’, while in ‘Sugar Plum’ addition of NAA increased shoot fresh weight and improved shoot quality rating without any effect on shoot number.

Open Access

Abstract

Shoots harvested from the first and 2nd reculture of azalea (Rhododendron sp.) accession 800374 shoot tip cultures grown under 16 hr photoperiod from cool-white fluorescent light were taller and achieved higher quality ratings than shoots from 24 hr daily photoperiod. The number of shoots produced during the first reculture was the same for both 16 and 24 hr photoperiod, whereas significantly more shoots were harvested from cultures grown under 16 hr in the 2nd reculture. Similarly, 24 hr light inhibited elongation of shoots and decreased quality rating from in vitro-derived shoot cultures without any effect on the number of shoots per culture. Photosynthetic photon flux density (PPFD) of 30 and 75 μmol s−1m−2 (400–700 nm) increased number, length, and quality rating of shoots harvested from in vitro-derived shoot explants when compared to a 10 μmol s−1m−2 PPFD. However, recultured in vitro-derived shoot explants produced similar number and length of shoots under 10, 30, and 75 μmol s-1m-2, whereas the quality rating was reduced in cultures under 75 μmol s−1m−2. The highest percentage of rooting occurred in microcuttings harvested from cultures grown under 10 and the lowest under 75 μmol s−1m−2. Increasing the PPFD from 10 to 75 μmol s−1m−2 reduced shoot length and quality rating of rooted microcuttings, as well as root length and quality rating.

Open Access

Abstract

Sphagnum peat (peat) media (adjusted to pH 4.0, 4.6, 5.5, 6.6, and 7.4 with ground dolomitic limestone) and unadulterated peat (pH 3.6) were tested for their effectiveness on rooting of hardy deciduous azalea (Rhododendron sp.) microcuttings in high-humidity chambers. Rooting of more than 90% occurred in media with pH 4.0, 4.6, and 5.5; however, a) shoot height and quality rating and b) root length and quality rating were superior at pH 4.0. Clonal differences in rooting percentages were found for 3 clones of azalea microcuttings rooted in 5 soilless mixtures. A mixture including equal parts (v/v) of peat and either sphagnum, vermiculite, or perlite, or a combination of 2 peat : 1 vermiculite : 1 perlite (by volume) increased rooting percentages over peat alone for all 3 azalea clones examined.

Open Access