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Wilhelm Rademacher and Toni Bucci

Plant growth regulators (PGRs) account for only a few percent of the worldwide sales of crop protectants. In recent years, most companies have drastically reduced their activities in the PGR area. The factors that have been of major relevance in this development are: a) Finding, developing and marketing a new PGR is more difficult and requires a considerably higher input as compared to other types of crop protectants, b) many segments of the market are fairly saturated with competitively priced products, and c) intensified legislation for the registration of new, and the re-registration of established products, has become a severe constraint, due to its absorbing large working and financial capacities. For these and other reasons, new types of PGRs will be economically viable only under certain circumstances, such as: a) A sufficiently large and profitable market guarantees a reasonable return on investment, b) costs for registration can be reduced by developing naturally occurring compounds, which may require considerably less toxicological and eco-toxicological studies, and c) PGR-like side activities of an existing herbicide, fungicide or insecticide can be exploited, which would, again, significantly reduce the costs for registration.

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Diane M. Camberato, James J. Camberato, and Roberto G. Lopez

Chemical PGRs are commonplace in the horticulture industry, having been used commercially since the 1940s ( Nickell, 1994 ). In high-value floriculture crops, PGRs are used in combination with cultural and environmental control methods to produce

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Duane W. Greene

Plant growth regulators that are made available to University researchers usually come with an indication of biological activity, based upon in-house work by chemical companies. Often a practical use of the PGR is suggested. The PRG is applied at a range of concentrations at a timing that is appropriate to get the desired response. Undesirable side effects are noted. Follow up experiments are designed, usually altering concentration, time of application, or formulation, to maximize a response or to overcome and alleviate undesirable side effects. If the PGR is labeled, refinements for its use and grower recommendations are prepared. Critical in the development process is communication and interaction among researchers and industry personnel. This is exemplified by the exchange of ideas, sharing of data, and brain-storming that has occurred over the past 25 years at the Northeast Plant Growth Regulator Working Group meetings. Budget reductions and down sizing of programs at the University have forced researchers to depend more upon grant-in-aid support from companies. Several case studies will be presented to show the commercial development of some PGRs, including: Accel, cultar, Apogee, and ReTain. The evolving role of researches in the development of PGRs will be discussed.

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John M. Ruter

Decline of certain container-grown ornamental species during the hottest months of summer is a common problem for nurserymen in the southeastern United States. When roots are killed due to high root-zone temperatures and growth ceases, production of plant hormones also decreases. A study was conducted with Early Harvest PGR (Griffin LLC, Valdosta, Ga.), which contains cytokinins, gibberellic acid, and indole butyric acid, to determine if this product would improve the growth of five ornamental species that typically decline during the summer in south Georgia nurseries. The species used were Cotoneaster dammeri Schneid. `Coral Beauty', Cotoneaster salicifolius Franch. `Green Carpet', Spiraea japonica L. `Shirobana', Thuja occidentalis L. `Little Giant', and Weigela florida (Bunge) A. DC. `Minuet'. The treatments (control, 1.5 and 3.0 mL Early Harvest PGR/1125 mL water) were applied every 2 weeks from mid-June until mid-Sept. 1999 as a foliar drench. Treatment of both Cotoneaster species and the Thuja with Early Harvest PGR resulted in little influence on plant growth. While growth indices did not increase, shoot dry mass of Spiraea and Weigela increased 17% and 26%, respectively, when treated with Early Harvest PGR at the medium rate. Plant quality ratings for Spiraea increased when the 1.5-mL rate of Early Harvest PGR was applied. A rate of 3.0 mL of Early Harvest PGR on Spiraea decreased shoot and root dry mass, total biomass, root ratings, and final plant quality. Root ratings and plant quality were highest for Weigela grown with the 1.5-mL Early Harvest PGR treatment. These results indicate that treatment of woody ornamentals with Early Harvest PGR for positive results is both species- and rate-dependent.

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Derek D. Woolard*, Judy Fugiel, F. Paul Silverman, and Peter D. Petracek

Tables, graphs, and photographs can effectively convey detailed results of a PGR experiment. However, we have observed that demonstrating PGR treatment effects by time-lapse video creates a strong impact on both scientists and non-technical audiences. Time-lapse video also provides a method for obtaining a continuous visual record that can be used to establish the precise chronology of a slow process. Recent advances in notebook computers, inexpensive digital cameras (e.g. 3Com HomeConnect™), and time-lapse software (e.g. Picture WorkLive™) allow scientists and teachers to inexpensively prepare time-lapse videos. Important considerations for the production of quality time-lapse videos include: 1. treatment effects should be substantial, consistent, and visible, 2. digital camera images should be clear, 3. lighting should be constant and provide adequate brightness and proper color, 4. camera movement such as those due to vibrations should be minimal, 5. camera placement should simplify composition. Time-lapse videos of PGR treatment effects will be shown, and methods of production will be discussed.

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Jeffrey S. Beasley, Bruce E. Branham, and Loretta M. Ortiz-Ribbing

Trinexapac-ethyl (TE) [4-(cyclopropyl-a-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] effects on turfgrass root architecture are not known. It has been postulated that PGR application could cause photoassimilate that is normally used for shoot growth to be funneled to root growth. This study evaluated the effects of a single TE application on kentucky bluegrass (KBG) root and shoot growth for seven weeks. Individual KBG plants were grown in a hydroponic system and harvested weekly. At each harvest, tiller height, tiller number, and color ratings were recorded. Estimates of total root length (TRL), root surface area (SA), and average root diameter were measured using the WinRhizo system. Trinexapac-ethyl reduced plant height for 4 weeks followed by a period of postinhibition growth enhancement. Trinexapac-ethyl increased tiller number over the course of the study and slightly enhanced plant color. Trinexapac-ethyl reduced TRL and SA 48% and 46% at 1 week after treatment (WAT) followed by an accelerated growth rate 1 to 4 WAT. Trinexapac-ethyl had no effect on root diameter. On a tiller basis, TE initially reduced TRL and SA 30% and 31%, respectively. Total root length per tiller and root surface area per tiller were reduced by TE treatment, but by 7 WAT, those differences were no longer significant. Initial reductions in TRL and SA per tiller may reduce tiller competitiveness for water and nutrients. Based on data for TRL and SA per tiller, shoot and root growth must be considered in total to fully understand TE effects on plant growth. Field research is needed to corroborate results from hydroponic-studies and examine the effect of various TE rates and multiple applications on turfgrass root and shoot growth.

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James P. Syvertsen

, and other plant growth regulators (PGRs) affect root–shoot communication, growth and quality of individual plants and their populations. Examples of root–shoot communication include tree fruits, crop plants, succulents, native plants, and the model

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Benjamin Wherley and Thomas R. Sinclair

, J.B. 1973 Environmental and cultural preconditioning effects on water use rate of Agrostis palustris Huds., cultivar Penncross Crop Sci. 13 424 427 Syngenta Professional Products 2008 Primo MAxx® pgr linked to fuel and

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Alexander D. Pavlista

Nitroguanidines are a new family of synthetic plant growth regulators (Speltz, Walworth, and Pavlista 1986. US Patent #4, 594, 092) These compounds have cytokinin-like activity such as delaying senescence. Three compounds are AC239, 604, AC243, 419 and AC132, 654 The first two are phenyl and the latter is a benzyl nitroguanidine. Examples of anti-senescence activity of these compounds are: 1. sunflower leaves, 2. tobacco leaves, 3. leafy lettuce, 4. kale, 5. collards, and 6. Swiss chard. The senescence of cut ornamental flowers is also inhibited. Examples are gladiolus and daffodils. Along with delaying senescence, AC239, 604, for example, increased leaf size, thereby, increasing yield of leaf crops such as tobacco (Pavlista and Templeton. 1987. PGRSA Proc.) and lettuce.

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Rebecca E. Scoville and Todd P. West

The objective of this study was to investigate the effects of multiple nutrient salt formulations and different plant growth regulator concentrations on initiation and proliferation of axillary shoot culture of tropical hibiscus (Hibiscus rosa-sinensis L.). Combinations of five thidiazuron (TDZ) concentrations (0, 10-6, 10-7, 10-8, or 10-9 M) in conjunction with two 6-benzylaminopurine (BA) concentrations (0, 10-5 M) and two indole-3-butryic acid (IBA) concentrations (0, 10-5 M) were compared to determine which plant growth regulator combination(s) would stimulate the proliferation of the most viable axillary shoots. Also, five nutrient salt formulations (MS, 1/2 MS; Macro MS, WPM, LP, or DKW) ranging from high to low salt formulations were studied to determine a suitable nutrient medium formulation for axillary shoot proliferation. Nodal explants that were 2 cm in length were used to initiate cultures and were maintained on the various medium treatments plus 30 g·L-1 sucrose and 7 g·L-1 agar at a pH of 5.8. Explants were incubated about 30 cm beneath cool-white fluorescent lamps that provide a photon flux of about 40 μM·m-2·s-1 for a 16-hour photoperiod at 25 ± 3 °C. Nodal explants were transferred every 3 weeks for a total culture period of 12 weeks. At each transfer date data were collected on node number, axillary shoot number and length. Initial results indicate that high nutrient salt formulations coupled with low TDZ concentrations performed better at axillary shoot initiation. Poor shoot elongation was observed and further research needs to be performed to address this issue.