Controlling Poinsettia (Euphorbia pulcherrima Will.) Height with Growth Retardant Application in West Java, Indonesia

A study was conducted to evaluate the effects of the growth retardant cycocel application in the growth and development of poinsettia (Euphorbia pulcherrima) ‘Freedom Red’. Cycocel was applied by spraying plant shoots at the concentrations of 1000, 1500, 2000, 2500 ppm. The increase in cycocel concentrations reduced plant height, leaf size, internodal length, plant spread and the number of fl owering plants. All cycocel concentrations resulted in an ideal potted plant height. The optimum spray concentration of cycocel used to obtain compact and uniformly fl owering plants under tropical West Java environment was 1000 ppm.


Introduction
Poinsettia (Euphorbia pulcherrima), or kastuba (Indonesian local name) is an indigenous plants from Mexico, South America.The colorful and most attractive portions of the plant are actually modifi ed leaves called bracts (Adams et al., 1995).These bracts may be red, pink, white, yellow, speckled or marbled; but the most popular color is red.The actual fl owers are located in the center at the base of the bracts.The fl owers are also known as cyathium and have separate male and female fl owers.Potted poinsettias are ready to market when the cyathia open and the stamens or styles protrude from the fl owers (Kessler, 2005).Poinsettia red bracts and green foliage and is widely used in Christmas fl oral displays (Hartley, 1992).The demand for potted poinsettias in Indonesia increases every year especially during the Christmas season.

Poinsettia pot plants have been produced
commercially in a number of nurseries in West Java, Indonesia.It is classifi ed as a short day plant that is they will fl ower and develops bracts only during long nights or during longer dark durations.However, the critical night period varies with cultivars and temperature.Naturally, poinsettias may grow up to 3 m in height; hence its growth should be controlled if it is grown as an pot plant to allow for a more proportionate pot plant (Krisantini et al., 2014).Tall poinsettia plants could also be a result of tall cuttings; too close spacing and inadequate light during its growth.Therefore, controlling plant size is important for potted ornamental plant production to get attractive and compact pot grown plants, which will ease packing and sleeving, and are more space effi cient for transportation (Krisantini et al., 2014).
Growing poinsettia in the warmer temperatures need growth retardant application to slow down stem elongation as application of plant growth retardant can control plant height through inhibition of biosynthesis of gibberellin, a group of plant hormone that control cell elongation (Rademacher, 1995;De Lucas et al., 2008).Retardants can be applied by spraying the shoots of the plants, or by drenching the potting media (Prue and Gregory, 2002).A study by Lopes and Berg (2003) had shown the effectiveness of several retardants such as A-Rest, B-Nine, Bonzi, Cycocel, or Sumagic to control poinsettia height.In addition, Niu et al. (2002) reported that drenching 100 mL per pot of 1 ppm of paclobutrazol was effective to control poinsettia height.
A preliminary study to evaluate the effects of paclobutrazol on controlling poinsettia 'Prestige' height in the tropics was conducted in 2008 to 2009 showed that paclobutrazol at 1 ppm sprayed twice during the early growth of poinsettia was effective in reducing fi nal plant height (Yulistyo et al., 2009).Paclobutrazol is a plant growth retardant from the triazole group which has strong activity.Paclobutrazol reduced internode elongation to give shorter stems, and was effective in tomato, pepper, fruit trees and
Cycocel or chlormequat (2-chlorethyl) trimethylammonium chloride is less strong compared to the triazole group.Cycocel is widely available in Indonesia and mainly used for ornamentals, including bedding plants and herbaceous crops.
The recommendation rates mentioned by previous researchers were specifi c for temperate climates however, little is known about the effectiveness of these compounds in the tropical regions where plants grow relatively faster due to warmer temperatures.Therefore, the objective of the current study is to determine the effects of cycocel on controlling poinsettia 'Freedom Red' height grown in the tropical West Java environment, and to determine the optimum cycocel concentration to obtain an optimum height of potted poinsettia without affecting its fl owering and bract size.

Materials and Methods
Experiment was conducted in 2010 to 2011 at Saung Mirwan nursery in Sukamanah Village, Pasir Muncang (-7.7200 S, 108.1722E), located in the highland area of West Java, Indonesia.Poinsettia cuttings of six to eight nodes were rooted in styro foam then transplanted into 15 cm pots containing rice hull charcoal and cocopeat media (1:1 v/v).Plants were pinched at two weeks after planting.The different concentrations of cycocel (1000, 1500, 2000 and 2500 ppm) were applied by spraying the shoot until runoff at four weeks after planting.This was done on a weekly basis for a total of nine weeks.In this study there was no untreated plants as it has already established that without growth retardant application poinsettia plants will grow to >1 m in height.
The experiment was set up in a complete randomized block design with the cycocel concentration as a single factor.Every treatment was replicated three times and every replicate consists of three plants.Planting distance were about 35 cm between plants and between rows.Plants were placed in a greenhouse with long-day environment by setting up lighting from 8 pm to 4 am at week 1 to week 8, followed by shortday environment using black polyethylene covers at 4 pm to 8 am daily at week 8 to week 15.
Scoring was conducted on plant height at 11 weeks after planting (WAP), leaf size, internode length, and stem diameter at six WAP, number of fl owering plants and plant spread at 15 WAP.Data was analysed using Statistical Analysis System (SAS) version 9.1.

Results and Discussion
Increased cycocel concentration reduced plant height, leaf size and internode length (Table 1).Cycocel application also affected the generative development of poinsettia.In addition, not all plants that were treated with high concentrations fl owered during the period of this study as only seven percent of the plants fl owered (Table 2).
Plant's spread, measured as the longest distance between the two outer leaves of each plant was reduced with increasing cycocel concentrations (Table 2).The ideal height of a pot plant is generally twice the container height (Kessler, 2005).In this study, all cycocel concentrations produced an ideal proportion of plant to the pot size; however considering that the highest concentration reduced fl owering, lower concentrations of Cycocel is recommended.
In our previous study, 1 ppm paclobutrazol applied as a soil drench during the crop growing period signifi cantly reduced poinsettia height and the diameter of bracts.Cycocel in the current study was equally effective to reduce poinsettia height but with different concentrations and application methods.Cycocel at concentration of >1000 ppm on a weekly interval for nine weeks have been proven to be effective in reducing poinsettia height.According to IFAS (2011) growth retardant application by spraying usually gives greater activity in the warm climates.Niu et al. (2002) reported that drench application may reduce poinsettia bract size, and delayed application may induce this undesired response.
Similar study by Youssef and Abd-El-Al (2013) showed that cycocel and paclobutrazol at similar concentrations were effective in controlling the growth of a popular perennial ornamental pot plant Tabernaemontana montana.Therefore, the results derived from this study are in line with other similar studies reported around the region.

Conclusion
Application of cycocel at 1000 ppm in this study was successful to achieve good plant size with less effect on bract development; thus showing the effectiveness of cycocel to control poinsettia height, reduced internode length, stem diameter and plant spread.A high concentration of 2500 ppm delayed fl owering; however, these results may vary with cultivars, depending on how vigorous the plants are and the climate where poinsettia is grown.

Table 1 .
Vegetative growth of Poinsettia 'Freedom Red' after Cycocel treatment* : 1) Plant height was measured at 11 weeks after planting, whereas leaf size, stem diameter and internodal length was measured at 6 weeks after planting (WAP).The values showing the same letter in the same column are not statiscally different from each other according to Duncan Multiple Range Test (p=0.05).