Sarhad J. Agric. Vol.29, No.3, 2013 PLANT GROWTH REGULATORS AND NON-INDUCTIVE PLANT ENVIRONMENT EFFECT ON GROWTH AND PLANT HEIGHT OF FACULTATIVE LONG DAY ORNAMENTAL ANNUALS JALAL-UD-DIN BALOCH 1 , MUHAMMAD MUNIR 2* , NAQIB ULLAH KHAN 3 and SAMRIN GUL 3 1. Dept. of Horticulture, Faculty of Agriculture, Gomal University, Dera Ismail Khan - Pakistan 2. Frontier Agriculture, SOYL Division, Recommendations Dept., Newbury - United Kingdom 3. Dept. of Plant Breeding and Genetics, The University of Agriculture, Peshawar - Pakistan *Correspondace author: muhammad.munir@soyl.co.uk ABSTRACT Seeds of facultative long day plants (Snapdragon cv. Coronette, Petunia cv. Dreams and Annual Verbena cv. Obsession) were sown into module trays containing leaf mould compost. After 70% emergence, two experiments were conducted to control plant height. In the first experiment, the plants of each cultivar were treated with standard dose of widely applied plant growth regulators i.e. A-Rest (Ancymidol) 30 ppm, Bonzi (Paclobutrazol) 30 ppm and Cycocel (Chlormequat) 1000 ppm and control. In second experiment, plants of same cultivars were kept under short day (SD) non-inductive environment for 2, 4, 6 and 8 weeks. After each time scale, these plants were then transferred to their long day (LD) inductive environment chamber until flowering. Results revealed that all the three plant growth regulators significantly (p0.05) reduced plant height of facultative long day plants as compared to control. Similarly, plants placed for a short duration (2 weeks) under SD non-inductive environment produced more or less similar results. However, if taller plants are required then this duration can be extended up to 8 weeks to obtain maximum plant height. The advantage of preferring non-inductive environment technique to plant growth regulators is that it is non-hazardous, environment friendly and less expensive. Keywords: Facultative long day ornamental annuals, plant growth regulators, Short and long day inductive environments, plant height Citation: Baloch, J.U.D., M. Munir, N.U. Khan and S. Gul. 2013. Plant growth regulators and non-inductive plant environment effect on growth and plant height of facultative long day ornamental annuals. Sarhad J. Agric. 29(3): 351-357 INTRODUCTION Most of annual ornamentals tend to grow taller than desired height and require using control measures i.e. application of plant growth regulators, cool temperatures, withholding fertilizer and water, to adjust the crop timing to meet the market requirement. However, when deciding the best method, the growers should consider the cost, the effect on crop scheduling and the effect on plant quality, in the retail outlet and with the consumer (Townsley-Brascamp and Marr, 1995; Kelley et al., 2001). The plant growth regulators such as A-Rest, B-Nine, Bonzi, Cycocel, Sumagic and Ethephon are used to control plant height on commercial scale. However, besides reducing height, plant growth regulators can make plants more compact, darken leaf color, curtail new leaf expansion and extend the life of certain species (Holt and Jennings, 1999). The residual effects of the plant growth regulators can even last until the plant’s roots become fully established. Most of the available plant growth regulators are anti-gibberellins and inhibit gibberellin synthesis within the plant that is responsible for cellular elongation (Magnitskiy et al., 2006; Lund et al., 2007; Lykas et al., 2008). Studies revealed that a number of non-chemical methods could control the height of floricultural plants as the hazard and costs of RGRs is increased. Among non-chemical plant height control methods, one of the easiest ways to reduce height and the need for plant growth regulators treatment is to manipulate light environment (Keever and Kessler, 2005; Lykas et al., 2008). Higher light intensity tends to retard plant elongation in most long day plants, resulting in shorter plants at maturity. Interest in non-chemical techniques is also increasing because of the tighter controls placed by the government on the use of agricultural chemicals and the public's negative perception of chemicals in general. Consumer’s interest is also varies from plant to plant such as dwarf sized poinsettia is highly preferred (Heins and Fisher, 1992; Whipker and Hammer, 1994; Clifford et al., 2004) whereas plant height of three times pot diameter of bedding and cut flower plants are ideal for garden or indoor beautification (Schnelle et al., 1992; Incrocci et al., 1994). To cater effectively the preference of consumers, those involved in the production, development or marketing of ornamentals need to be aware of the relative importance of their choice for specific plant height. Keeping in view this objective, present research study was therefore designed to compare chemical (plant growth regulators) and non-chemical methods (duration under non-inductive light environment) and their effect on plant height of facultative long day plants.