Optimizing Seed Germination and Growth of Seedlings in Persian Walnut

The efficiency of conventional stratification methods for seed germination of walnut (Juglans regia L.), which uses long moist-chilling periods, is low. This experiment was conducted during winter to spring 2014 to optimize the seed germination of walnut ‘Chandler’ via changing growing media and removing seed mechanical dormancy. Fourteen treatments were tested. None of the seeds germinated without any treatment on shell or while they stored in manure. Germination percent of cracked seeds (CS) and cracked with toothpicks inserted seeds (CTS) without any stratification period reached up to 66.1% and 83.7% with mean germination time (MGT) of 0.73 and 0.98 day, respectively. Considering a 45-day cold storage period improved germination percentage of CS and CTS up to 88.3% and 94.1% with MGT of 1.02 and 1.12, respectively. Seedling growth parameters significantly increased after the cold storage period. Based on the results, mechanical dormancy was suggested as the main limiting factor for walnut seed germination. Therefore, rate and percentage of seed germination and seedling growth of walnut can be improved if the removal of mechanical dormancy is also considered in seed stratification.