WALNUT GRAFTING SUCCESS AS AFFECTED BY DIFFERENT GRAFTING METHODS, CULTIVARS AND FORCING TREATMENTS

Persian walnut (Juglans regia L.) is one of the most difficult to propagate species. To find the most suitable procedure for walnut grafting out of season, different bench grafting methods (side stub, omega and whip tongue) were evaluated in four walnut varieties (‘Z₅₃’, ‘Hartley’, ‘Pedro’ and ‘Serr’). In addition, the effect of forcing pre-treatment on grafting components (placing of grafting components in a forcing room at a temperature of 26-28°C and relative humidity of 80-90% for two weeks (rootstocks) or 3 days (scions) before grafting) was assessed using the side stub grafting method in two varieties (‘Hartley’ and ‘Pedro’). All experiments were repeated twice during 2006 and 2007. The grafted plants were covered with moist sawdust, providing a relative humidity of 85-90%, and stored in a humid room with a temperature of 26-28°C for 21 days. The omega grafting method had the highest average callus score (2.61 out of 4), number of callused grafts (82.22%), graft take (71.11%) and graft survival (81.03%). In the second experiment, the effect of stocks and scions pretreatment (forcing) were significant on the callus rate, graft take and graft survival characters. In this experiment, grafted plants treated with the forcing pre-treatments showed the highest callused grafts (82.7%), graft take (73.8%) and grafting survival (71.9%). Treating of grafting components with forcing pre-treatments under controlled conditions increase grafting success considerably.