Removing Mechanical Dormancy Improves Seed Germination and Early Growth of Walnut ‘Chandler’

Improving sexual propagation is an important aspect for preserving genetic resources. Seed germination of many walnut varieties such as ‘Chandler’ is low even after long moist-chilling periods. The aim of this study was optimizing seed germination of walnut ‘Chandler’ by changing growing medium and removing mechanical dormancy. Fourteen treatments were tested in the experiment. None of the seeds without any treatment on shell, and the seeds placed in manure germinated. Germination percentage of cracked seeds (CS) and cracked with toothpicks-inserted seeds (CTS) without stratification period reached up to 66.1% and 83.7% with mean germination time (MGT) of 0.73 and 0.98, 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 also significantly increased after cracking. Based on the results, mechanical dormancy was suggested as the main limiting factor of poor seed germination of walnut ‘Chandler’. Therefore, rate and percentage of seed germination and seedling early growth of walnut will be improved if the removal of mechanical dormancy is also considered in seed stratification.