Abstract Optimization of medium components in in vitro cultures is very difficult because of having multifactor nature. To optimize the plant growth regulator concentrations (BA, IBA, GA3) for shoot proliferation of apple cv. ‘Abbasi’ a threefactor experiment was designed and performed in 20 points (20 treatments) using Design Expert software based on the response surface method. A completely randomized design using eight auxin combinations (IBA+NAA) was also carried out for in vitro rooting of microcuttings. Proliferated shoot number was linearly and positively affected by the BA factor, while the response of the leaf number was linearly and negatively affected by BA. The effect of GA3 on proliferated shoot length was negative and linear. The abnormal shoot percentage in a quadratic model was influenced by all three types of PGRs, i.e. BA, IBA and GA3; positively and linear by BA, positively and quadratic by IBA and negatively and quadratic by GA3. According to the results of this experiment, the optimum concentrations for BA, IBA and GA3 combination were 1.5, 0.1 and 0.02 mg L-1, respectively, which resulted in the proliferated shoots with a rate of 2.5 shoots per explant, with 0.9 cm in length, 4.3 leaves per shoot and 4% abnormal shoots. The percentage of shoot-tip necrosis was not affected by the evaluated factors. NAA was more effective than IBA for rooting microcutings. The medium supplemented by 1 mg L-1 IBA or 0.5 mg L-1 NAA can be used successfully for rooting of apple cv. ʽAbbasiʼ shoots in vitro.

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