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Carole H. Saravitz, Frank A. Blazich, and Henry V. Amerson

Adventitious shoots developed on cotyledons of Virginia pine (Pinus virginiana Mill.) excised from seeds subjected to H2O2 treatment for 3, 6, or 9 days and cultured on media containing 0.5 to 10 mg BA/liter. Shoot regeneration was greatest (42 shoots per embryo) on cotyledons from seeds treated with H2O2 for 6 days and placed on medium containing BA at 10 mg·liter-1. Excised shoots elongated on medium lacking BA. Following elongation, shoots were placed on media containing IBA at 0 to 40 mg·liter-1 for 14 days followed by transfer to the same medium lacking auxin. Without IBA treatment, rooting was 3%, and increased to 50% for 5 to 40 mg·liter-1. Rooted shoots averaged 2.0 roots per shoot without auxin incorporation, 3.3 roots when treated with 5 mg IBA/liter, and the number of roots increased linearly with increased IBA concentration up to 40 mg·liter-1 (4.5 roots). Plantlets were transferred to growing medium and acclimated successfully to greenhouse conditions. Chemical names used: N- (phenylmethyl)-1 H- purine-6-amine (BA), 1 H- indole-3-butyric acid CBA).

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Dennis P. Stimart and James F. Harbage

The role of the number of adventitious roots of Malus domestics Borkh. `Gala' microcuttings in vitro on ex vitro root and shoot growth was investigated. Root initiation treatments consisted of IBA at 0, 0.15, 1.5, 15, and 150 μm in factorial combination with media at pH 5.5, 6.3, and 7.0. IBA concentrations significantly influenced final root count and shoot fresh and dry weights, but not plant height, leaf count, or root fresh and dry weights at 116 days. Between 0 and 0.15 μm IBA, final root counts were similar, but at 1.5, 15, and 150 μm IBA, root counts increased by 45%, 141%, and 159%, respectively, over the control. The pH levels did not affect observed characteristics significantly. There was no significant interaction between main effects. A significant positive linear relationship was found between initial and final root count. The results suggest a limited association between high initial adventitious root count and subsequent growth. Chemical name used: 1 H -indole-3-butyric acid (IBA).

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Benyamin Lakitan, David W. Wolfe, and Richard W. Zobel

Greenhouse experiments were conducted in 1987 and 1988 to evaluate the effect of timing of a 4-day flooding stress on growth and yield of snap bean (Phaseolus vulgaris L. cv. Bush Blue Lake 274, BBL). Plant survival was reduced when flooding was imposed at postflowering growth stages, but most plants survived when flooded before flowering or when reproductive development was prevented by deflowering. Early yields of surviving plants were very low in all flooded treatments, regardless of timing, in both years. Total yield response to timing of flooding was linear in 1987, with lowest yields when flooding was imposed at later growth stages. The trend was not linear in 1988, but in both years the latest flooding treatment (36 days after planting) had few surviving plants and no measurable pod yield. Additional greenhouse experiments revealed that leaf conductance of BBL and another bean cultivar, Luna (LN), declined within the first day of flooding. This decline was concomitant with one in leaf water potential and photosynthesis (Pn) in BBL, but decline of these responses occurred 1 to 2 days later for LN. After 4 days of flooding, Pn fell to near 0 for BBL, and to 15% of the prestress value for LN. Pn of both cultivars had recovered to 18.5 μmol·m-2·s-1 10 days after termination of flooding. LN had a larger adventitious root biomass, higher percentage of adventitious roots, and a consistently lower leaf: root ratio than BBL during recovery.

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Wenhao Dai and Victoria Jacques

Periwinkle, a perennial commonly used as a summer bedding plant, is known as the source of vinca alkaloids used to treat lymphocytic leukemia and Hodgkin's disease. It is also one of the natural hosts of many phytoplasma diseases, such as X-disease of major Prunus species, aster yellows, and ash yellows diseases. Therefore, periwinkle is an ideal plant species for phytoplasma disease research, such as disease transmission, species resistance, and resistant gene screening. Periwinkle tissue culture was established by incubating sterile seeds in hormone-free Murashige and Skoog (MS) medium. Plants were successfully regenerated from in vitro leaf tissues of periwinkle. Adventitious shoots were induced when leaf tissues were cultured on Murashige and Skoog (MS) medium or woody plant medium (WPM) supplemented with benzyladenine (BA) and naphthaleneacetic acid (NAA). Nearly 75% of leaf explants produced shoots in both media with 10–20 μm BA and 1 μm NAA. A mean of 4.3 shoots was produced from each explant cultured on WPM, whereas only 2 shoots were produced on MS medium under 16-h photoperiod. Leaf explants under dark treatment for 2 weeks produced big callus only, indicating that light is necessary for shoot formation. Most adventitious shoots were induced from the joint of leaf blade and petiole. In vitro shoots (>1.5 cm) were easily rooted in half-strength MS medium. Addition of NAA dramatically increased root number, with more than 20 roots being induced in 5 μm NAA medium. Rooted plants were transferred to potting medium and grown in a greenhouse.

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Steven T. McNamara and Cary A. Mitchell

The relative contributions of auxin and ethylene (C2H4) in stimulating the initiation of adventitious root primordia (ARP) and their subsequent development into adventitious roots (ARs) by flooded tomato (Lycopersicon esculentum Mill. PI 406966) seedlings were evaluated using TIBA and STS. Flooded plants treated with STS (F + STS) produced ≈ 40% as many emerged ARs as plants that were flooded only (F). Only 7% of the ARP initiated by F + STS plants developed enough to emerge through the epidermis by 120 hours of treatment compared with 95% emerged for F plants. A band of TIBA applied below the lowest leaves of flooded plants (F + TIBA) virtually eliminated AR formation. Plants with two or four leaves below the TIBA band produced 16- and 35-fold more ARs, respectively, than those with no leaves below the TIBA band. Relative to nonflooded (NF) plants, F + STS plants exhibited a nearly 40-fold increase in C2H4 evolution, while F and F + TIBA plants exhibited about a 5-fold increase in C2H4 production. These results suggest that auxin accumulation at or above the floodline is essential for ARP initiation and that auxin action is not mediated through C2H4. Ethylene may be required for elongation of flood-induced ARP leading to their emergence as ARs. Chemical names used: 2,3.5 -triiodobenzoic acid (TIBA): silver thiosulphate (STS).

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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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J.T.A. Proctor, T. Slimmon, and P.K. Saxena

Ginseng is an herbaceous perennial that grows in the understorey of deciduous hardwood forests and is also cultivated for its highly valued root. The primary method of propagation of ginseng is by seed which requires the breaking of dormancy by stratification, a process which takes 18–24 months. Investigation of factors controlling the growth and development of ginseng plants is a prerequisite to the development of a more efficient system of ginseng propagation. We have recently modulated the morphogenetic potential of geranium roots and stimulated de novo development of shoots and embryo-like structures which later formed whole plants using thidiazuron (TDZ). Our objective was to investigate the morphological changes in seedling and mature ginseng plants induced by TDZ, particularly in relation to root and shoot morphogenesis and economic yield. Applications of TDZ (0.22 and 2.20 ppm), either as foliar sprays or soil watering to greenhouse-grown seedlings over 18 weeks (2 weeks after sowing to 20 weeks when plants were harvested) induced similar effects. These responses included increased stem length and diameter, and shoot and root weight (economic yield). Single foliar applications of TDZ at 62.5 and 125 ppm to 3-year-old field-grown ginseng plants 3 months before harvest increased root biomass (economic yield) by 19% to 23%. Roots of TDZ-treated seedlings and 3-year-old field-grown plants developed thickened secondary roots on the upper part of the taproot. The root-like structure of these secondary roots was confirmed by histology. In addition, TDZ treatments induced adventitious buds on the shoulder of 3-year-old roots. These buds developed into shoots to give multi-stem plants following a period of dormancy, which was overcome with GA3 (gibberellic acid) treatment before planting.

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Michael A. Arnold and Eric Young

Bare-root Malus × domestica Borkh. seedlings were chilled for 0, 600, 1200, or 1800 hours at 5C (CH). Seedlings were then placed with roots and/or shoots in all combinations of 5 and 20C forcing conditions (FC) for up to 21 days. Virtually no growth occurred at 5C FC. When the whole plant was forced at 20C, all measures of root and shoot growth increased in magnitude, occurred earlier and at a faster rate with increasing CH. Thus, roots and shoots responded similarly to chilling. When shoots or roots were subjected to 20C FC, while the other portion of the plant was at 5C, the responses were reduced in magnitude and delayed. However, the overall growth enhancement by chilling was not negated. Root and shoot growth enhancement by chilling appeared to be increased if the other portion of the plant was actively growing also, but not dependent on it. Growth of adventitious shoots on roots (root suckers) was greatly enhanced with increasing CH on plants subjected to 5C shoot and 20C root FC. While total root and shoot bark protein levels on a per-seedling basis were similar, protein concentrations were lower in root bark than in shoot bark. During chilling, total protein per seedling generally increased until just before the time that chilling requirements for vegetative budbreak were satisfied. Protein degradation then began, resulting in lower protein levels through 2300 CH. Rapid protein breakdown (1200 to 1800 CH, roots; 1000 to 1800 CH, shoots) occurred at about the same time that root (1000 to 1800 CH) and shoot (800 to 1800 CH) growth responses to chilling were increasing. Warm FC resulted in increased protein breakdown with increased CH and forcing time.

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Carole H. Saravitz, Frank A. Blazich, and Henry V. Amerson

Adventitious shoots developed on cotyledons of Virginia pine (Pinus virginiana Mill.) excised from seeds germinated for 3, 6, or 9 days and cultured on media containing 0.5 to 10 mg/liter benzyladenine (BA). Shoot regeneration was greatest (46 shoots per embryo) on cotyledons from seeds germinated for 6 days and placed on medium containing 10 mg/liter BA. Shoots were excised and elongated on medium lacking BA. Following elongation, shoots were placed on media containing 0 to 40 mg/liter indolebutyric acid (IBA) for 14 days followed by transfer to the same medium lacking auxin. Without IBA treatment, percent rooting was 3% and increased to 50% for concentrations of 5 to 40 mg/liter. Rooted shoots averaged 2.0 roots per shoot without auxin treatment, 3.3 roots when treated with 5 mg/liter IBA and root number increased linearly with increased IBA concentration up to 40 mg/liter (4.5 roots). Plant lets were transferred to growing medium and acclimated successfully to greenhouse conditions.

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Carole H. Saravitz, Frank A. Blazich, and Henry V. Amerson

Adventitious shoots developed on cotyledons of Virginia pine (Pinus virginiana Mill.) excised from seeds germinated for 3, 6, or 9 days and cultured on media containing 0.5 to 10 mg/liter benzyladenine (BA). Shoot regeneration was greatest (46 shoots per embryo) on cotyledons from seeds germinated for 6 days and placed on medium containing 10 mg/liter BA. Shoots were excised and elongated on medium lacking BA. Following elongation, shoots were placed on media containing 0 to 40 mg/liter indolebutyric acid (IBA) for 14 days followed by transfer to the same medium lacking auxin. Without IBA treatment, percent rooting was 3% and increased to 50% for concentrations of 5 to 40 mg/liter. Rooted shoots averaged 2.0 roots per shoot without auxin treatment, 3.3 roots when treated with 5 mg/liter IBA and root number increased linearly with increased IBA concentration up to 40 mg/liter (4.5 roots). Plant lets were transferred to growing medium and acclimated successfully to greenhouse conditions.