The Effect of Gibberellic Acid and Chilling Stratification on Seed Germination of Eastern Black Walnut (Juglans nigra L.)

Eastern black walnut (Juglans nigra L.) is used as a rootstock for the Persian walnut (Juglans regia L.) in some parts of the world and also has an important role in forestry and wood industry. Due to the deep physiological dormancy, the seed often shows an inconsistent or low germination percentage, making establishment difficult. This experiment was carried out as a completely randomized design with eight treatments and 16 replicates in a controlled greenhouse. The objective of this study was to determine the best treatment of breaking dormancy. Treatment groups consisted of seed priming with GA3 (400 and 800 ppm) solution for 24 hours, chilling stratification (one month and two months) and the combined treatments of chilling stratification and GA3. Results showed that the germination rate for separate application of both concentrations of GA3 and one month chilling treatment was zero, as no seeds germinated. The highest percentage of seed germination (69.27 %) was recorded with the combined treatment of two months chilling and GA3 (400 ppm). Also, this treatment showed significant differences for morphological, physiological and biochemical parameters compared to other treatments. It was found that the application of the combined treatment of chilling stratification and GA3 was effective in increasing seed germination percentage and rate as well as improving growth parameters of Eastern black walnut seedlings.