Proceedings of the 4 th International Conference on Agriculture and Forestry, Vol. 3, 2017, pp. 1-5 Copyright © 2017 TIIKM ISSN 2362-1036 online DOI: https://doi.org/10.17501/icoaf.2017.3201 Corresponding Authors’ Emails: 1 anushab@sltc.edu.lk and 2 gdonkk@yahoo.com APPLICATION OF CYTOKININ AND GIBBERELLIC ACID TO REGULATE FLOWER QUALITY IN Dendrobium ORCHID Anusha Bogahawatta 1 and Kapila Kumara 2 1 Sri Lanka Technological Campus, Sri Lanka 2 Sabaragamuwa University of Sri Lanka, Sri Lanka Abstract: This study was conducted to evaluate the effect of plant growth regulators on enhancing the flower quality of a selected Dendrobium cultivar at the mid country wet zone, Sri Lanka. The sole and combination effects of Gibberellic Acid3 (GA3), 6-Benzylaminopurine (6BAP) hormones and the effect of drench and spray modes of application were tested. The experimental design was Randomized Complete Block Design (RCBD) and each treatment contained five replicates and five plants per replicate. Data on average sepal, petal and labellum lengths and widths and area of the flower were collected on the fourth day after full blooming. Time taken for blooming was counted when the flower bud reached 3 mm diameter to the full blooming stage. Sole application of 125 mg/L GA3 and the combination of 125 mg/L GA3 + 200 mg/L 6BAP were able to reduce the days taken for blooming. Length to width ratio of petal, sepal, and labellum was minimum at 200 mg/L 6BAP and it enhanced the visual appearance. Sole application of 125 mg/L GA3 increased petal, sepal, and labellum lengths, whereas 200 mg/L 6BAP increased the petal, sepal, and labellum widths and area of the flower. Among the modes of applications tested for 200 mg/L 6BAP, spraying was found better than drenching. Study results conclude that spraying 125 mg/L GA3 can be used to achieve early blooming. The area of the flower, petal, sepal, and labellum sizes can be manipulated according to the flower characters and market demand. Keywords: Drench, Flower quality, Plant growth regulators, Spray Introduction Dendrobium orchids are popularly used in cut flower industry as they come in a wide range of vibrant colors, its ability to recurrent flowering and being able to produce a high number of flowers per inflorescence (Aziz, 2009). Among them, white color Dendrobium has a huge demand from florists since they can be sprayed with vibrant colors of artificial floral dyes. The cultivar, D. ‘Jaq Hawaii’ x D. ‘Singapore White’ is extremely popular among Sri Lankan farmers due to its ability to produce a large number of white color flowers per inflorescence and frequent flowering. For the production of beautiful, long-lasting and large size blooms, orchids must produce energy in the form of carbohydrates during the day when the temperature is high and store that energy at night when the temperature drops. Without a Diurnal Temperature Variation (DTV) of 10-12 °Ϲ, the plants will grow plenty of healthy foliage, but flowers produced are small in size or the plant may refuse to flower (Lee and Lin, 1984). In Sri Lanka, due to sudden daytime rain throughout a considerable period of time per year, it has become difficult to provide the plants with relevant day-night temperature fluctuation. This was identified as a huge problem for most of the orchid growers in the mid country wet zone-Sri Lanka. The process of flowering in tropical orchids can be described in two ways: flower induction and floral development. Induction of flower is influenced by genetic, environmental and physiological factors. Following induction, the flower bud will grow and its subsequent growth will depend on the supply of photoassimilates from various sources (Bernier, 1988). The influence of plant hormones in concern of these photoassimilates was that GA3 like plant hormones stimulate the transport of photoassimilate through the phloem, increase sucrose uptake, or act on the metabolism of sucrose and its metabolic products (Arthur and Morris, 1984). The function of Cytokinin in plants is to promote cell division. However, there are specific instances where Cytokinin also