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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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James T. Brosnan, Adam W. Thoms, Gregory K. Breeden, and John C. Sorochan

, whereas soil compaction negatively alters soil physical properties ( Carrow and Petrovic, 1992 ). Plant growth regulators (PGRs) have been defined as organic compounds that alter turfgrass growth or development by targeting the actions of plant hormones

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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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Josh B. Henry, Ingram McCall, and Brian E. Whipker

limit plant height and promote overall compactness. Growers typically manage excessive stem elongation with chemical growth regulators such as PGRs ( Whipker, 2017 ). A concern associated with PGRs is that they are not labeled for all crops. PGRs also

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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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Zhongjie Ji, James J. Camberato, Cankui Zhang, and Yiwei Jiang

, reduced Na + uptake, and maintenance of K + uptake ( Munns and Tester, 2008 ). Hence, salinity tolerant plants often have higher K + and lower Na + accumulation under salinity stress ( Tang et al., 2013a , 2013b ) PGRs are strongly involved in the

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Kellie J. Walters and Roberto G. Lopez

specifications for shipping, and produce compact, well-branched, and aesthetically appealing plants, greenhouse growers use a wide variety of chemical plant growth regulators or retardants (PGRs) ( Blanchard and Runkle, 2007 ; Currey et al., 2016a ). The most

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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.

Open access

Irfan Ali Sabir, Xunju Liu, Songtao Jiu, Matthew Whiting, and Caixi Zhang

the density of pollenizer trees are two cultural practices that growers may use to address problems with pollenizers and low fruit sets. Applying PGRs to extend the successful pollination period is an additional or complementary solution to enhance

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Leo G. Albrigo and Ed W. Stover

fruit on the tree ( Ali-Dinar et al., 1976 ; Ferguson et al., 1982 ). Thus, auxins and other plant hormones such as GA affect citrus physiology and the effects of endogenous plant hormones can be mimicked by PGRs. Measurement of ethylene levels in