THE EFFECTS OF DIFFERENT IN VITRO AND EX VITRO TREATMENTS ON THE ROOTING PERFORMANCE OF PERSIAN WALNUT (Juglans regia L.) MICROSHOOTS

Rooting is the main limiting factor in the micropropagation of Persian walnut (>I>Juglans regia>/i> L.) due to the poor rooting capacity of this species. A number of experiments were conducted to identify suitable procedures for rooting of walnut microshoots. Rooting was done in two successive phases: A) root induction and B) root development. In the first experiment root induction was done on DKW medium (1/4-strength macronutrients) containing four different concentrations of IBA or NAA (2, 3, 4 and 5 mgl-1) in darkness. After one week, for root development, shoots were transferred to a mixture of hormone free medium and vermiculite (20 ml of medium and 25 cm3 vermiculite). The maximum rooting (37.5%) was obtained on medium containing 4.0 mgl-1 IBA. Treatments containing IBA were better for rooting than those containing NAA. In another experiment for root induction shoots were cultured on DKW medium (1/2-strength macronutrients) containing 0.5 mgl-1 IBA and 3.0 gl-1 activated charcoal for three weeks under lighted conditions. Then, the basal end of shoots were dipped in talcum powder containing different concentrations of IBA and were transferred to Jiffy-7 pots. Maximum rooting (23.25%) was obtained by basal dip immersion of shoots in talcum powder containing 1.5% or 2% IBA. The effects of other in vitro and ex vitro treatments were also studied. The best results were obtained by culturing the microshoots on DKW medium (1/2-strength macronutrients) containing 4.0 mgl-1 IBA for 9 days in darkness and transferring to Jiffy-7 pots for root development without auxin treatment. Using this procedure about 83% of surviving shoots in Jiffy-7 pots rooted, which is applicable for mass propagation of Persian walnut. The use of Jiffy-7 pots allowed rapid development of the root system and improvement in the quality of plantlets (higher number of roots, presence of secondary roots), and root development was synchronised with shoot elongation and development of new leaves. On transferring the plantlets to the greenhouse their growth continued and more than 90% of plantlets survived.