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Gouchen Yang and Paul E. Read

BA, IBA and GA3 were incorporated into softwood tissues to be cultured in vitro or rooted as cuttings by adding the plant growth regulators (PGR) at various concentrations to a forcing solution containing 200 mg/l 8-hydroxyquinoline citrate and 2% sucrose. BA and GA3 helped break bud dormancy in autumn-collected stems and increased percent bud-break. IBA inhibited bud break and shoot elongation. Rooting of forced softwood cuttings was enhanced by IBA in the forcing solution, while GA3 inhibited the rooting of plant species tested. When dormant stems were forced with periodic additions of BA (10 mg/l) in the forcing solution, in vitro shoot proliferation was enhanced. However, inclusion of GA3 in the forcing solution reduced shoot proliferation. A pre-forcing NaOCl soak and a pre-forcing treatment with wetting agents accelerated bud break, size and number of shoots available for both micro- and macro-propagation of the woody plant species tested. The forcing solution protocol described is an effective PGR delivery system and it can be used by the propagator to extend the season for obtaining softwood growth suitable for use as in vitro explants or softwood cuttings.

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Billy J. Johnson

Two separate experiments (one and two applications and dates of treatment) were conducted on plant growth regulator (PGR) injury and seedhead suppression of centipedegrass [Eremochloa ophiuroides (Munro) Hack.]. Mefluidide caused less injury to centipedegrass than either imazethapyr or flurprimidol + mefluidide. Mefluidide applied at 0.56 kg·ha-1 in each of two applications at 2-week intervals suppressed seedheads of centipedegrass for 10 weeks. A single 0.56-kg·ha-1 application of the mefluidide failed to suppress seedheads when applied any time from mid-June until late July. A single treatment with flurprimidol + mefluidide severely injured centipedegrass, and seedhead suppression was poor regardless of date of treatment. Centipedegrass was severely injured when flurprimidol + mefluidide was applied at 1.68 + 0.28 kg·ha-1 in each of two applications, but seedheads were suppressed for 10 weeks. Imazethapyr applied at 0.30 and followed by 0.15 kg·ha-1 suppressed seedheads 10 weeks after treatment in 1987 and 6 weeks after treatment in 1988 without reducing turf density. When this PGR was applied as a single treatment at 0.30 kg·ha-1, seedhead suppression was generally greater for 8 weeks when applied mid- to late July than mid- to late June. Chemical names used: N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]amino]phenyl]acetamide (mefluidide); α -(1-methylethyl)- α -[4-(trifluoromethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol); and (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxlic acid (imazethapyr).

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Sushobitbir Singh Thind, Harmander Pal Singh, and Sukhdev Singh

Peach [Prunus persica Batsch. (L.)] is a major fruit of northern India, which is commercially propagated through stem cuttings. There is a scarcity of information available on the effect of plant growth regulators (PGRs) and time of plantings on rooting of peach stem cuttings. Studies were conducted to learn the effects of various PGRs and planting times on stem cuttings of peach cv. Shan-i-Punjab at the fruit nursery of the Horticulture Department, Khalsa College, Amritsar, India, in 2001 and 2002. The study on stem cuttings, taken from the middle portion of the shoot, compared three PGRs: indolebutyric acid (IBA), indoleacetic acid (IAA), and naphthaleneacetic acid (NAA), each at concentrations of 50, 100, and 200 mg·L-1 and two planting dates (20 Dec. and 20 Jan.). Cuttings were treated for 24 hours before keeping under moist sand for 1 month for callusing. Callused cuttings were planted in the field. Measurements on sprouting percentage, survival percentage, plant height, shoot diameter, number of leaves per plant, leaf size, average root length, and root weight per cutting were recorded. The study showed that, overall, auxins had significant effect on the success and rooting character of peach plants over the control. The greatest sprouting and survival percentage, plant height, leaf area, and shoot diameter was exhibited by IBA followed by IAA and NAA. IBA at 100 ppm proved to be the most suitable PGR for improving success along with other rooting and vegetative characters of the plant. The cuttings planted on 20 Dec. gave a higher percentage of success (55.32%) over those planted on 20 Jan. (33.04 %), during both years of study. The other plant characteristics, such as average root length, plant height, leaf area, and plant height, of cuttings planted on 20 Dec. also showed greater success during both years.

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Katayoun Mansouri and John E. Preece

A factorial combination of gibberellic acid (GA3) and benzyladenine (BA) was applied in 20% white exterior latex paint to large (40 cm long, >2.5 cm diameter) stem segments of Acer saccharinum L. (silver maple) to determine the effects on forcing new softwood shoots in the greenhouse or laboratory and the subsequent growth of these new shoots in vitro. Stem segments were harvested from 10-year-old field-grown coppice shoots. The GA3/BA-paint mixes were applied to the entire stem segments that were forced in plastic flats filled with 1 perlite: 1 vermiculite (by volume) and watered with care so as not to wet the new softwood shoots. The flats and stem segments were drenched weekly with Zerotol (0.18% H2O2). The softwood shoots were harvested when they were at least 3 cm long. After disinfesting and rinsing, the nodal and shoot tip explants were established aseptically in vitro on DKW medium with no cytokinin or with 10-8M thidiazuron. Coppice shoots were harvested, cut, and painted on 9 Sept., 28 Oct., and 12 Dec. 2005. Although there were no significant differences in shoot production among stem segments painted with various combinations of GA3/BA, stems treated with plant growth regulators produced a mean of 2.7, 1.8, or 0.5 shoots for the three harvest dates compared to 0.5, 0.0, or 0.25 shoots on control stem segments. It is well-known that shoot forcing is poor from September through January; however, use of GA3/BA resulted in growth of dormant epicormic shoots. Shoot tip explants produced the most shoots in vitro after 8 weeks if they were harvested from stem segments treated with 0.03 mM GA3, whereas nodal explants produced the most shoots if harvested from segments that had been treated with 0.01 mM GA3.

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Aristidis S. Matsoukis, Ioannis Tsiros, and Athanasios Kamoutsis

The effect of various plant growth regulators on leaf area development of Lantana camara L. subsp. camara was investigated under three photosynthetic photon flux (PPF) conditions (100%, 72%, and 34% light transmittance). The triazole compounds paclobutrazol (0, 50, 100, 200, and 500 mg·L-1) and triapenthenol (175, 350, 700, and 1400 mg·L-1), as well as the onium-type compounds mepiquat chloride (125, 250, 500, and 1000 mg·L-1) and chlormequat chloride (750, 1500, 3000, and 6000 mg·L-1), were applied as foliar spray solutions in each PPF level after pinching the plants. Leaf area, in general, decreased logarithmically as the concentrations of paclobutrazol and triapenthenol increased at all PPF levels. On the other hand, PPF reduction was found to increase leaf area of lantana plants treated with all concentrations of each regulator. Leaf area reduction of the paclobutrazol and triapenthenol treated plants at all PPF levels exceeded 60% compared with that of nontreated plants. However, the corresponding reduction was 22%, up to 51% for the plants treated with mepiquat chloride and chlormequat chloride. These results indicate that the triazole compounds have a greater effect on the reduction of lantana leaf area than the onium-type compounds. Chemical names used: (2RS, 3RS)-1-(4-chlorophenyl)-4, 4-dimethyl-2-(1H-1, 2, 4-triazol-1-yl) pentan-3-ol (paclobutrazol); (E)-(RS)-1-cyclohexyl-4,4-dimethyl-2-(1H-1, 2, 4-triazol-1-yl) pent-1-en-1-ol (triapenthenol); 1,1-dimethyl-piperidinium chloride (mepiquat chloride); (2-chloroethyl) trimethylammonium chloride (chlormequat chloride).

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E.W. Stover and D.W. Greene

Plant response to foliar application of plant growth regulators (PGRs) is often variable, in part due to environmental factors. Weather prior to application is thought to influence cuticle development and thus PGR uptake. For example, in growth chamber studies foliar uptake of 1-naphthaleneacetic acid (NAA) is sometimes increased when fruit trees are placed in low temperature and high humidity several weeks prior to application. Environmental conditions over an extended period of time after application may influence PGR conversion to active form (e.g., ethephon), PGR metabolism, or metabolic factors that affect PGR activity in the plant. The effects of environmental conditions on PGR uptake have been investigated extensively in laboratory studies. In many cases, uptake is clearly increased by high temperatures immediately after application. Laboratory studies report a linear positive correlation between temperature and uptake and greater temperature response above 25 °C (77.0 °F). High humidity and longer drying time often are also reported to increase PGR uptake in laboratory studies. These results are consistent with many grower observations on effects of weather on chemical thinning and have been incorporated into many product labels and extension recommendations. However, relatively few field experiments have been reported in which the relationship between PGR response and environmental conditions were assessed. Wash-off studies have demonstrated that rain shortly after application may reduce efficacy of NAA. Several studies demonstrate environmental interaction with metabolic activity involved in PGR action. For example, shading after thinner application is reported to increase fruitlet abscission and enhance effectiveness of some thinning agents. Chemical thinning of apples (Malus ×domestica) with ethephon is reported to correlate strongly with temperature in the days after application, while studies suggest that higher temperatures after aminoethoxyvinylglycine (AVG) application may reduce control of preharvest drop. However, the stage of fruitlet development at apple thinning often appears to be more important than environmental conditions at the time of PGR application. In addition, field experiments indicate that longer drying times at lower temperatures seem to largely compensate for greater uptake rates at higher temperatures. This paper discusses data from published and previously unpublished experiments in order to understand the effects of environment on PGR response variability.

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Emily A. Clough, Arthur C. Cameron, Royal D. Heins, and William H. Carlson

Influences of vernalization duration, photoperiod, forcing temperature, and plant growth regulators (PGRs) on growth and development of Oenothera fruticosa L. `Youngii-lapsley' (`Youngii-lapsley' sundrops) were determined. Young plants were vernalized at 5 °C for 0, 3, 6, 9, 12, or 15 weeks under a 9-hour photoperiod and subsequently forced in a 20 °C greenhouse under a 16-hour photoperiod. Only one plant in 2 years flowered without vernalization, while all plants flowered after receiving a vernalization treatment, regardless of its duration. Thus, O. fruticosa had a nearly obligate vernalization requirement. Time to visible bud and flower decreased by ≈1 week as vernalization duration increased from 3 to 15 weeks. All plants flowered under 10-, 12-, 13-, 14-, 16-, or 24-hour photoperiods or a 4-hour night interruption (NI) in a 20 °C greenhouse following 15-weeks vernalization at 5 °C. Time to flower decreased by ≈2 weeks, flower number decreased, and plant height increased as photoperiod increased from 10 to 16 hours. Days to flower, number of new nodes, and flower number under 24 hour and NI were similar to that of plants grown under a 16-hour photoperiod. In a separate study, plants were vernalized for 15 weeks and then forced under a 16-h photoperiod at 15.2, 18.2, 20.6, 23.8, 26.8, or 29.8 °C (average daily temperatures). Plants flowered 35 days faster at 29.8 °C but were 18 cm shorter than those grown at 15.2 °C. In addition, plants grown at 29.8 °C produced only one-sixth the number of flowers (with diameters that were 3.0 cm smaller) than plants grown at 15.2 °C. Days to visible bud and flowering were converted to rates, and base temperature (Tb) and thermal time to flowering (degree-days) were calculated as 4.4 °C and 606 °days, respectively. Effects of foliar applications of ancymidol (100 mg·L-1), chlormequat (1500 mg·L-1), paclobutrazol (30 mg·L-1), daminozide (5000 mg·L-1), and uniconazole (15 mg·L-1) were determined on plants vernalized for 19 weeks and then forced at 20 °C under a 16-h photoperiod. Three spray applications of uniconazole reduced plant height at first flower by 31% compared with that of nontreated controls. All other PGRs did not affect plant growth. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); (2-chloroethyl) trimethylammonium chloride (chlormequat); butanedioic acid mono-(2,2-dimethyl hydrazide) (daminozide); (2R,3R+2S,3S)-1-(4-chlorophenyl-4,4-dimethyl-2-[1,2,4-triazol-1-yl]) (paclobutrazol); (E)-(S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pent-1-ene-3-ol (uniconazole).

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Richard H. Zimmerman and George L. Steffens

Tissue-culture (TC)-propagated `Gala' and Triple Red `Delicious' apple trees grown at three planting densities were not treated (CON) or treated with plant growth regulators (PGRs) starting the third or fourth season to control tree size and maximize fruiting. `Gala' and `Delicious' trees budded on M.7a rootstock (BUD) were also included as controls. `Gala' trees were larger than `Delicious' after the first three growing seasons but `Delicious' were larger than `Gala' at the end of 9 years. BUD trees were larger than CON trees the first few seasons hut final trunk cross-sectional area (TCSA) of CON trees averaged 43% greater than BUD trees. Paclobutrazol and uniconazole treatments more readily controlled the growth of `Gala' than `Delicious' and uniconazole was more effective than paclobutrazol in controlling tree size. Daminozide + ethephon sprays (D+E-S) did not influence tree size. Tree size of both cultivars was inversely related to planting density and both triazole PGRs were more effective in controlling tree size as planting density increased. The trees had fewer flowers as planting density increased and BUD trees generally had more Bowers than CON. Triazole PGRs had little effect on the flowering pattern of `Gala' trees but tended to stimulate flowering of young `Delicious' TC trees, although the increases were not sustained. The D+E-S treatment increased flowering of `Gala' trees the last 3 years of the experiment and consistently increased flowering of `Delicious' TC trees. Fruit yields were higher for young `Gala' compared to `Delicious' trees and the final cumulative yield per tree for `Gala' was also greater. Yield per tree decreased as tree density increased and was the same for BUD and CON trees. D+E-S increased cumulative per tree yield of `Delicious' but not of `Gala'. Cumulative yields per tree for triazole-treated TC trees were the same as, or significantly lower than, CON trees. Increasing tree density did not increase yield/ha. Yield efficiency of `Gala' trees was increased by three, and of `Delicious' trees by one, of the triazole treatments, because they reduced TCSA proportionally more than they reduced per tree yield. There was less bienniality with `Gala' than `Delicious' and no difference between BUD and CON trees. Bienniality indices were higher for paclobutrazol-treated `Gala' trees compared with CON `Gala' but only uniconazole applied as a trunk paint increased the bienniality index of `Delicious' trees. Chemical names used: succinic acid-2,2-dimethyl hydrazide (daminozide), (2-chloroethyl) phosphonic acid (ethephon), (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-01 (paclobutrazol), (E)-(l-chlorophenyl)-4,4-dimethyl-2-(I,2,4-triazol-l-yl)-1-penten-3-ol (uniconazole).

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Amy Lynn Bartel and Terri W. Starman

Angelonia angustifolia `Blue Pacific', Asteriscus maritimus `Compact Gold Coin', and Heliotropium aborescens `Fragrant Delight' are three vegetatively propagated species of annuals. The objective of this study was to find which plant growth regulator chemicals could be used to control height and produce compact, well-branched, flowering plants. The plants arrived as rooted plugs and were transplanted to 10-cm plastic containers. When the roots of the transplanted plugs reached the edge of their containers, 15 days after transplanting, the plant growth regulator chemicals were applied. Five different chemicals were used in spray applications at two rates measured in mg/L: ancymidol at 66 and 132; daminozide at 2500 and 5000; paclobutrazol at 20 and 40; ethephon at 500 and1000; and uniconazole at 10 and 20. One drench application of uniconazole at 1 and 2 mg/L and one control (water spray) were also used. Total plant height, plant width, flower number, node number, stem length, internode length, and numbers of days to visible bud were recorded. Ancymidol at both rates caused stunting and flower distortion in asteriscus; however, it was not effective on angelonia or heliotrope. Paclobutrazol and uniconazole sprays were ineffective in controlling height on all three species. Ethephon at both rates was effective in controlling height, and producing well-branched plants in all three species, yet it caused a delay in flowering. Uniconazole drench at both rates was also effective in controlling height but caused stunting. In general, daminozide at 5000 mg/L was most effective in controlling foliage height without a delay in flowering or decrease in flower size or number in all three species.

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Y.D. Park, H.S. Kim, and B.K. Kang

The development of genetic transformation systems has led to remarkable progress in the area of plant molecular biology. This has included the introduction of useful traits, such as resistance to viruses, herbicides, and insects. Transformed plant cells can be selected, using chimeric genes that confer resistance to toxic drugs, such as kanamycin, hygromycin, streptomycin, gentamycin, and bleomycin. Expression of these chimeric genes in the transformed cells confers the ability to survive and proliferate on the selective medium, while non-transformed cells die. In this study, we report a simple and efficient system to regenerate Chinese cabbage plants and study of the effects of plant growth regulators, AgNO3, initial dark treatment, various antibiotics, and herbicide on shoot induction from hypocotyl or cotyledon of Chinese cabbage. Shoots were induced at various combinations of naphtalene acetic acid (NAA) and benzyladenine (BA) levels. The best combination of plant growth regulators was 2.0 mg/L NAA and 1.0 mg/L BA for cotyledon, and 1.0 mg/L NAA and 5.0 mg/L BA for hypocotyl. The experiment investigating the effect of AgNO3 demonstrated that 16.7 mg/L AgNO3 was effective for inducing shoot regeneration from both of explants. Three to five days of initial dark treatments had significant effects for increasing the number of regenerated shoots; however, different growth regulator combinations showed various responses to duration of dark treatments. The effects of kanamycin, hygromycin, cefatoxime, carbenicillin and phosphinothricin (PPT) on shoot induction from cotyledon and hypocotyl were tested. Shoot induction was completely inhibited by kanamycin at 10 mg/L, hygromycin at 5 mg/L, PPT at 5 mg/L or higher, but not by carbenicillin and cefatoxime.