Claudio C. Pasian
The effectiveness of applying a plant-growth regulator as a paint/paclobutrazol mixture coating the interior surface of wedge cells was evaluated. Cuttings of three poinsettia (Euphorbia pulcherrima, Willd. ex Klotzsch) cultivars ('Red Sails,' 'Nutcracker Pink,' and 'Nutcracker White') were rooted in wedge cells painted with a paint/paclobutrazol mix. Significant reductions in cutting heights were observed at most paclobutrazol concentrations. No signs of phytotoxicity were attributed to either paclobutrazol or the paint. These preliminary results suggest that the application of paclobutrazol in paint to the interior of wedge cells may be used to control the height of cuttings while they are being rooted. Chemical name used: b-((4-chlorophenyl) methyl)-a-(1,1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).
Appreciation is expressed to Possum Run Greenhouses for rooting cuttings in their production facilities.
Plant growth regulators are usually applied as drenches or sprays to poinsettia plants to maintain plant height in proportion with container size. Cuttings of vigorous cultivars may grow more than desired during the rooting process, especially if they remain in the wedges too long after rooting (e.g., transplanting delayed by lack of elements such as pots, labor, space, etc., or delayed shipping of the cuttings by the propagator).
Although not widely used, growth regulators in poinsettia cutting production may be very important for cultivars that stretch during the rooting process. The stretch tendency is compounded by crowding of cuttings in the wedges. Overlapping of plant parts reduces light intensity and changes light quality, resulting in light below plant canopies that is richer in near-infrared and far-red which encourages plant stretching. While drenching is the most effective application method for some growth regulators (e.g., paclobutrazol), it is impractical for the rooting of cuttings. Spraying, on the other hand, is possible but has some problems. BonziĆ must be sprayed on the stems in order to be fully effective. Since cuttings are located very close to each other on the rooting wedges, reaching the stems with the sprays is not always easy. Developing a new method of growth regulator application to cuttings may provide growers with a more efficient and cost effective way of using paclo-butrazol on rooting poinsettia cuttings.
The concept of using copper-coated interior containers to control root growth was introduced in the 1970s. Roots exposed to copper-treated surfaces absorb high amounts of copper (Arnold and Struve, 1989). Pasian and Struve (1996) showed that plant growth regulators could also be delivered using containers with coated interiors. They demonstrated that plant height of chrysanthemum [Dendranthema grandiflora (Ramat)] could be controlled using containers whose internal surface is coated with a paint/paclobutrazol mixture. The objective of this study was to determine the response of three poinsettia cultivars to paclobutrazol/paint mix applied to the interior of the wedge.
Paclobutrazol was stirred into two paints - a white interior flat latex paint (water solution of butyl acrylate/vinyl acetate copolymer, titanium dioxide, aluminum silicate, and amorphous silicate) and Spinout (Griffin Corp., Valdosta, Georgia) without the copper active ingredient specially prepared by the manufacturer for this experiment. After mixing each paint and paclobutrazol for 15 minutes, the mix (0.52 and 0.69 ml per cell for latex and Spinout respectively) was brushed uniformly onto the internal surface of plastic wedge cells. After painting, the cells were dried at room temperature for 24 hours before use.
The wedges (Oasis Grower Products, Kent, Ohio) had 17 cells that were filled with Oasis foam-medium with a central hole to support the unrooted poinsettia cutting. Wedge trays were divided into seven treatments - control (no paint and no paclobutrazol), paint only, and five paint/paclobutrazol mixes applied at rates of 12.5, 25, 50, 100, and 200 mg l-1 (6.5, 13, 26, 52, and 104 Fg a.i. per cell, respectively for the flat latex painted cells and 8.6, 17.3, 34.5, 69, and 138 Fg a.i. per cell, respectively for the Spinout painted cells). Poinsettia cuttings 'Nutcracker White' and 'Nutcracker Pink' were rooted during the summer of 1996; cuttings of 'Red Sails' were rooted in the summer of 1997. After sticking the cuttings in the Oasis foam, the wedges were placed on a commercial greenhouse grower's mist bench. Cutting height (the distance from wedge rim to the top of the apical bud) was measured with a ruler when cuttings were rooted. After measurement, cuttings of 'Nutcracker White' and 'Nutcracker Pink' were planted in 15 cm (1750 ml volume) plastic pots using a peat-light mix and located in a growing greenhouse to determine the duration of the plant growth regulator effect on plants.
Rate response to paclobutrazol was determined by regression analysis using the GLM procedure of SAS (SAS Inst., Cary, North Carolina). The same program was used to calculate the least significant difference for comparison among treatments.
Paint and/or plant growth regulator did not negatively affect above-ground appearance of the cuttings. Roots of cuttings rooted in the presence of paclobutrazol were shorter and thicker (larger diameter) than roots of control plants. 'Red Sails' cuttings rooted in cells painted with either paint (latex or Spin-out) without the growth regulator were shorter than control cuttings. This result requires further investigation.
Most cuttings subjected to paclobutrazol were significantly shorter than control cuttings (Table 1). 'Nutcracker White' cuttings were significantly shorter than control cuttings only when rooted in cells with the two highest concentrations of paclo-butrazol. Increasing paclobutrazol concentrations did not produce correspondingly shorter cuttings. This result contrasts with those presented by Pasian and Struve, 1996a and 1996b with chrysanthemums and plugs, respectively. In their work, they found that the rate response was highly significant. No explanation for this difference can be given based on the results presented in this work. Paint type (flat latex paint vs. Spinout) had no effect on 'Red Sails' cutting heights despite the fact that Spinout-painted cells had 32% more active ingredient than flat latex painted cells. Three weeks after pinching, transplanted plants in all treatments had the same heights, indicating that the growth regulator effect was short-lived.
The results obtained with 'Red Sails,' 'Nutcracker Pink,' and 'Nutcracker White' must also be validated with other cultivars. Until this method of application is described on the label of commercial growth regulators, it cannot be used by commercial growers.
| Table 1. Height after rooting of cuttings of three poinsettia cultivars. | ||||
|---|---|---|---|---|
| Treatment | Cutting Height (cm) | |||
| 'Red Sails'z (Latex) | 'Red Sails' (Spinout) | 'Nutcracker Pink' (Latex) | 'Nutcracker White' (Latex) | |
| Control | 7.5 a | 9.1 b | 6.9 a | |
| Paint only | 4.7 b | 5.1 b | 11.4 a | 8.7 a |
| 12.5 ppm | 3.9 bc | 5.0 b | 5.9 c | 6.0 bc |
| 25 ppm | 3.7 c | 4.3 bc | 5.9 c | 5.4 bc |
| 50 ppm | 3.2 c | 3.8 c | 5.2 c | 5.5 bc |
| 100 ppm | 3.5 c | 3.8 c | 5.0 c | 5.2 c |
| 200 ppm | 3.6 c | 3.6 c | 5.0 c | 4.9 c |
| Significance | ||||
| Linear model | ns | ns | ns | ns |
| Quadratic model | ns | ns | ns | ns |
| LSD | 0.995 | 0.994 | 1.26 | 1.23 |
| Height after rooting of cuttings of three poinsettia cultivars - 'Red Sails,' 'Nutcracker Pink,' and 'Nutcracker White.' 'Red Sails' cuttings were rooted in wedge cells painted with flat latex/paclobutrazol mixes. The 'Nutcracker' cuttings were rooted on wedge cells painted with a mix of two paints/paclobutrazol mixes - flat latex paint and Spinout without copper. | ||||
Arnold, A. A. and D. K. Struve. 1989. Cupric carbonate controls green ash root morphology and root growth. HortScience 24(2):262-264.
Pasian, C. C. and D. K. Struve. 1996a. Painted containers: a new method for paclobutrazol application. HortScience 31(4)655.
Pasian, C. C. and D. K. Struve. 1996. Paclobutrazol/Paint Mix on the Inside Surface of Plug Cells to Control Plug Height. Ohio Agricultural Research and Development Center. Special Circular 154. Ornamental Plants: Annual Reports and Research Reviews. January 1997. In partnership with Ohio State University Extension. pp. 66-69.