Available online freely at www.isisn.org Bioscience Research Print ISSN: 1811-9506 Online ISSN: 2218-3973 Journal by Innovative Scientific Information & Services Network RESEARCH ARTICLE BIOSCIENCE RESEARCH, 2018 15(3):2237-2246 OPEN ACCESS Gamma irradiation and gibberellic acid for improving of seed germination and seedling growth of koelreuteria paniculata laxm Hamdy M.A. El-Bagoury 1 , Mohamed M. M. Hussein 1 , Magdy A. El-Essawy 2 , Mahmoud F. Noby 2 and Noha K. El-Shahawy 2 * 1 Department of Ornamental Horticulture, Faculty of Agriculture, Cairo University, Egypt. 2 Plant Research Department, Nuclear Research Center, Atomic Energy Authority, Egypt. *Correspondence: nkhaled495@yahoo.com Accepted: 09 Sep2018 Published online: 26 Sep. 2018 Koelreuteria paniculata Laxm. (golden rain–tree) is propagated by seeds. However, natural germination is delayed because of morphological dormancy and physiological dormancy in seed coat and seed embryo. In this paper, the different methods for breaking seed dormancy were investigated. The treatments included different doses of gamma irradiation (0.0, 100, 150 and 200 Gy) and gibberellic acid (0.0, 50, 100, 200 and 400 ppm). Data were recorded on germination including; germination percentage, germination velocity, germination capacity, germination period and germination rate index. Furthermore, data on seedling growth after germination were recorded including plant height, number of main branches, shoot fresh and dry weights and root length. The chemical components (total carbohydrates, Chlorophyll-a, -b, total carotenoids, total soluble indoles and total soluble phenols) also were determined. The obtained results revealed that, there is a significant difference among the various methods used in breaking dormancy in seeds of Koelreuteria paniculata Laxm tree. Gamma irradiation and gibberellic acid stimulate germination and seedlings growth parameter and chemical components of Koelreuteria paniculata. Gamma irrradiation at 150 Gy was the optimum dose for improving the seedling growth, germination and chemical components. Moreover, gibberellic acid at 100 ppm was considered as suitable for improving germination parameter, seedling growth parameter and chemical component compared to control. From these results the use of γ-irradiation and gibberellic acid should be adopted in breaking Koelreuteria paniculata seed dormancy by farmers. Keywords: Koelreuteria paniculata, Germination, Seedling growth, Chemical component, Gamma radiation, Gibberellic acid, γ-irradiation. INTRODUCTION γ-irradiation influence plant growth by stimulation of morphological and physiological changes in tissues and cells (Moussa et al., 2015). Radiation has significant effects on both the size and the weight of plants. These effects depend on the intensity of radiation or the method in which the total dose in fractioned. Mainly, the biological influence of γ-irradiation is due to the free radicals formation by water hydrolysis, which may result in the modulation of an anti-oxidation system, accumulation of chlorophyll pigments and phenolic compounds (Wi et al., 2007; Ashraf, 2009 and Moussa et al., 2015). Treatment seeds of trees with low dose of γ-irradiation have been found to enhance seed germination and characteristic of seedling growth (Iglesias-Andreu et al., 2012 and Moussa, 2009). Koelreuteria paniculata Laxm (golden rain-tree) is a deciduous tree, because of beautiful yellow flowers which