Producers work year-round taking cuttings from herbaceous perennials. This task is difficult because perennials flower at different times of the year. Reproductive tissue on cuttings can inhibit root and vegetative development (Gibson and Cerveny, 2005); therefore, it is highly desirable to keep stock plants in a vegetative developmental state. Herbaceous perennial crops need to produce enough vegetative material to justify the cost of the space they occupy on the greenhouse bench. Furthermore, target uniformity is desired. Perennial producers often prune their plants manually to increase vegetative growth. However, manually pruning perennials to encourage vegetative growth can be labor-intensive (Banko and Stefani, 1996) and can add unwarranted expense (Holland et al., 2007). Producers have sought a more convenient approach to increase vegetative growth. However, PGRs have been less commonly used to enhance vegetative plant growth and remove reproductive tissue (Preece and Read, 1993). However, PGR applications are generally less labor-intensive than manual pruning, although phytotoxicity may be a problem for certain crops (Meijón et al., 2009). Three specific PGRs have been identified for their potential benefits for stock plant production: gibberellic acid, benzyladenine, and ethephon.
The GA4+7 treatment uniformly promotes growth primarily through cell elongation throughout plant tissue (Moore, 1984). Therefore, application of GA4+7 to promote plant growth could result in more propagation material from stock plants. Cytokinins, specifically benzyladenine, have been found to be involved in nearly all aspects of plant growth and development (Leopold and Kriedemann, 1975). Benzyladenine promotes cell enlargement, but not cell elongation as with auxins and gibberellins; therefore, it promotes cell growth in all directions (Preece and Read, 1993). This results in decreased apical dominance if cytokinin levels in the plant are increased (Hartmann et al., 2002). Increasing lateral growth could result in more propagation material from stock plants. Ethephon is an ethylene inducer that enters the plant and breaks down into three molecules: phosphate, chloride, and ethylene. Ethylene has many processes within the plant cell when released into plant systems that affect plant growth and reproductive development (Preece and Read, 1993). Ethephon is widely used to promote auxiliary shoot development without damage to the apical meristem (Hayashi et al., 2001). Increased branching and decreased flower development could result in more vegetative growth for herbaceous perennial stock plants.
Herbaceous perennial responses to PGRs vary across cultural and environmental conditions (Cochran and Fulcher, 2013). Applications of benzyladenine increased branching on ‘Ruby Star’ coneflower (Echinacea hybrid) at rates as low as 300 ppm (Latimer et al., 2011), but ‘Silver Lode’ coral bells (Heuchera hybrid) responded minimally to an application of 600 ppm (Latimer and Freeborn, 2015). ‘Snow Angel’ coral bells and Orange Carpet™ hummingbird trumpet (Epilobium canum ssp. garrettii ‘PWWG01S’) had similar results when treated with GA4+7, but the quality of cuttings had disparities (high quality and low quality, respectively) (Markovic and Klett, 2020). The wide range of possible plant responses indicates the importance of continuing the study of herbaceous perennial responses to PGRs.
Mojave sage (Salvia pachyphylla) and ‘Avalanche’ cape daisy (Osteospermum hybrid) are herbaceous perennials that were used during these experiments. Meetings with greenhouse and nursery operators propagating the two herbaceous perennials resulted in two main production problems with both perennials. These problems were a lack of quality vegetative propagation material from stock plants and low rooting percentage rates during propagation. Based on previous research, it was decided that using PGRs could help resolve these problems.
The main objective of this study was to evaluate vegetative and floral development of mojave sage and ‘Avalanche’ cape daisy after applications of three commercial PGRs with the active ingredients of gibberellic acid, benzyladenine, or ethephon. This study hypothesized that applications of PGRs would result in increased vegetative propagation material with quantity and quality similar to those of mojave sage and ‘Avalanche’ cape daisy stock plants and not affect rooting success.
Ackerman, R. & Hamernik, H. 1994 Gibberellic acid to extend shoots and bud break on Heuchera and Scabiosa Proc. Intl. Plant. Prop. Soc. 44 545 546
Banko, T.J. & Stefani, M.A. 1996 Growth response of large, established shrubs to cutless, atrimmec, and trimcut J. Environ. Hort. 14 177 181 doi: 10.24266/0738-2898-14.4.177
Brown, S.G. & Klett, J.E. 2020 Impacts of growth substrate and container size on cutting production from ‘Snow Angel’ coral bells stock plants HortTechnology 30 185 192 doi: 10.21273/horttech04495-19
Cochran, D. & Fulcher, A. 2013 Type and rate of plant growth regulator influence vegetative, floral growth, and quality of Little Lime™ hydrangea HortTechnology 23 306 311 doi: 10.21273/horttech.23.3.306
Gibson, J.L. & Cerveny, C.B. 2005 Stock plant production and management basics for small greenhouse businesses. Univ. Florida Ext. Bul. ENH1021. 15 Oct. 2020. <http://ufdcimages.uflib.ufl.edu/IR/00/00/17/42/00001/EP28400.pdf>
Grossman, M., Freeborn, J., Scoggins, H. & Latimer, J.G. 2012 Benzyladenine increases branching but reduces root growth of herbaceous perennial liners HortScience 47 1085 1090 doi: 10.21273/hortsci.47.8.1085
Hartmann, H.T., Kester, D.E., Davies, F.T. & Geneve, R.L. 2002 Plant propagation: Principles and practices. 7th ed. Pearson Education, Upper Saddle River, NJ
Hayashi, T., Heins, R.D., Cameron, A.C. & Carlson, W.H. 2001 Ethephon influences flowering, height, and branching of several herbaceous perennials Scientia Hort. 91 305 323 doi: 10.1016/s0304-4238(01)00225-4
Holland, A.S., Keever, G.J., Kessler, J.R. & Dane, F. 2007 Single cyclanilide applications promote branching of woody ornamentals J. Environ. Hort. 25 139 144 doi: 10.24266/0738-2898-25.3.139
Latimer, J.G., Freeborn, J. & Groover, V. 2011 Benzyladenine increases branching of herbaceous perennials Acta Hort. 886 192 198 doi: 10.17660/actahortic.2011.886.21
Latimer, J.G. & Freeborn, J. 2015 Improving quality of containerized herbaceous perennials with a tank mix of Configure and Piccolo E-GRO Alerts 4 5 192 198
Leopold, A.C. & Kriedemann, P.E. 1975 Plant growth and development. 2nd ed. McGraw-Hill, New York, NY
Markovic, S.J. & Klett, J.E. 2020 Increasing stock production of two herbaceous perennials with the application of plant growth regulators HortTechnology 30 421 427 doi: 10.21273/horttech04492-19
Martin, S.A. & Singletary, S. 1999 N-6_Benzyladenine increases lateral offshoots in a number of perennial species Proc. Intl. Plant. Prop. Soc. 49 329 334
Miller, W.B., Mattson, N.S., Xie, X., Xu, D., Currey, C.J., Clemens, K.L., Lopez, R.G., Olrich, M. & Runkle, E.S. 2012 Ethephon substrate drenches inhibit stem extension of floriculture crops HortScience 47 1312 1319 doi: 10.21273/hortsci.47.9.1312
Meijón, M., Rodrıquez, R., Canal, M. & Feito, I. 2009 Improvement of compactness and floral quality in azalea by means of application of plant growth regulators Scientia Hort. 119 169 175 doi: 10.1016/j.scienta.2008.07.023
Pearson, S., Parker, A., Hadley, P. & Kitchener, H.M. 1995 The effect of photoperiod and temperature on reproductive development of cape daisy (Osteospermum jucundum cv. ‘Pink Whirls’) Scientia Hort. 62 225 235 doi: 10.1016/0304-4238(95)00792-r
Preece, J.E. & Read, P.E. 1993 The biology of horticulture: An introductory textbook. Wiley, New York, NY
Rademacher, W. 2015 Plant growth regulators: Backgrounds and uses in plant production J. Plant Growth Regul. 34 845 872 doi: 10.1007/s00344-015-9541-6
Walters, K. & Lopez, R. 2018 The efficacy of ethephon foliar sprays is influenced by carrier water alkalinity and ambient air temperature at application HortScience 53 1835 1841 doi: 10.21273/hortsci13426-18