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Chemical promotion of branching and stem elongation of Poinsettia

In its native environment, poinsettia (Euphorbia pulcherrima) grows as a weak shrub or small tree that can reach 3 to 4 m and has red narrow bracts. Commercial growers have been able to capitalize on years of plant breeding to introduce refined cultivars that are shorter, fuller, and more visually appealing, while still possessing the intense colors of pink, orange, yellow, light green, white, and the hallmark holiday reds in the bracts. These attributes have made poinsettia one of the most economically important potted plants sold in the United States, with wholesale sales of more than $157 million, and have made poinsettias a staple of holiday d├ęcor and landscaping.

Traditionally, young poinsettia plants are pinched to remove the shoot tip, which forces the lower nodes to branch out. This results in a wider and fuller plant, but mechanical pinching is labor-intensive and may not be economically feasible in high-density production.

In a new study, researchers have documented a novel method for enhancing the growth of poinsettia plants. The study, conducted at North Carolina State University, explored chemical intervention approaches that could promote branching and stem elongation in poinsettias.

Through carefully controlled experimentation and data analysis, researchers showed that specific chemical compounds ( benzyladenine (BA), gibberellins [GA(4+7)] and dikegulac sodium) stimulate elongation and branching without compromising plant health or aesthetics.

When used properly, BA+GA(4 + 7) was found to be a good tool for increasing plant height, especially when used to offset the overapplication of PGRs. BA+GA(4+7) can be applied early in the crop season to increase height; however, for most cultivars, there will be a tradeoff with a delay in flowering. Drench applications of BA+GA(4 + 7) were less effective than foliar sprays, possibly because of the presence of bark in the substrate.

The use of dikegulac sodium proved effective in promoting lateral branching on nonpinched poinsettia plants and, in some cultivars, produced a plant similar in appearance to mechanically pinched plants. The best application time of was1 week before the standard pinching date of poinsettia. Caution should be taken with use of dikegulac sodium because it can significantly delay floral development, but this effect was variable and dependent on cultivar.

Comparison of dikegulac sodium applications with mechanical pinching on poinsettia growth and flowering times.

Comparison of dikegulac sodium applications with mechanical pinching on poinsettia growth and flowering times.

Cultivar

Treatment

Shoot #

Inflorescence #`

Days to flowering

Jubilee Red

Pinched

6.0

4.8

95

800 ppm once

9.0

4.4

93

1600 ppm once

11.00

5.4

99

800 ppm twice

13.0

6.0

94

Noel Red

Pinched

7.7

5.4

99

800 ppm once

15.7

5.2

100

1600 ppm

20.7

6.2

106

800 ppm twice

25.0

6.6

107

Prestige Red

Pinched

6.7

4.6

95

800 ppm once

10.0

4.2

94

1600 ppm

9.3

5.6

99

800 ppm twice

12.3

5.8

99

Prima Red

Pinched

7.3

5.0

99

800 ppm once

12.3

5.8

101

1600 ppm

14.7

6.0

100

800 ppm twice

18.3

7.2

101

Stargazer Red

Pinched

7.3

5.0

100

800 ppm once

11.0

6.8

103

1600 ppm once

14.0

6.4

105

800 ppm twice

16.3

5.8

102

Titan Red

Pinched

7.3

5.2

84

800 ppm once

11.3

5.4

84

1600 ppm once

11.0

5.2

90

800 ppm twice

12.0

6.6

86

Growers are advised to carefully assess the potential side effects of employing these chemicals, which can vary depending on the Poinsettia cultivar. It is essential to evaluate the specific cost-to-benefit ratio when selecting cultivars for production. As a precautionary measure, producers should conduct small-scale trials before integrating treatments into large-scale production operations, as is customary with any new production practice.

According to the author, "The greenhouse industry is always looking for ways to make production more efficient while still growing a high quality plant that lasts a long time for consumers. The research can help producers with the issues of pinching millions of plants as well as when plants are too short."

John Dole is a Professor of Horticultural Science at North Carolina State University.

Read the entire article on the ASHS HortTech electronic journal website at: https://doi.org/10.21273/HORTTECH05186-23

For more information:
American Society for Horticultural Science (ASHS)
ashs.org

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