Effects of Scion Cultivar, Rootstock Age and Hormonal Treatment on Minigrafting of Persian Walnut

The experiment was carried out during 2015-2016, with the aim of investigating the effects of scion cultivar, rootstock age and hormonal treatments on the success of walnut minigrafting. Analysis of results showed that all studied factors were effective on graft-take and survival of minigrafted walnuts and other growth traits of the scions. The highest graft-take was observed on one-year-old rootstocks in hormonal treatments of 20 mg/L BA + 12.5 mg/L IBA for ‘Jamal’ and 80 mg/L BA + 50 mg/L IBA for ‘Chandler’. The highest survival rate was observed on one-year-old rootstocks in control treatment and the lowest was on two-year-old rootstocks in hormonal treatment of 80 mg/L BA + 50 mg/L IBA. The highest growth rate of scion belonged to the scions of ‘Jamal’ on one-year-old rootstocks in hormonal treatment of 20 mg/L BA + 12.5 mg/L IBA and the lowest was in scions of ‘Chandler’ on two-year-old rootstocks in hormonal treatments of 20 mg/L BA + 12.5 mg/L IBA and 80 mg/L BA + 50 mg/L IBA. In addition, diameter of the graft union on two-year-old rootstocks was more than on one-year-old ones. Histological studies showed that increase in the diameter of the graft unit on two-year-old rootstocks was due to dead and necrotic tissues at the upper parts of it which acted as a barrier against passage of water and minerals from the rootstock to the scion and reduced the growth of the scion on two-year-old rootstocks.