Abstract
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 gamma-irradiation and gibberellic acid should be adopted in breaking Koelreuteria paniculata seed dormancy by farmers.