Abstract
Pear rootstocks play an important role in intensive orchards by influencing tree vigor, productivity, stress tolerance, and environmental adaptation. However, the response of pear rootstocks used in Kazakhstan to different in vitro culture medium formulations remains insufficiently characterized. This study evaluated six modified Murashige and Skoog medium formulations as complete treatment combinations for shoot multiplication and growth of the introduced clonal rootstocks OH×F₂₃₀ and OH×F₆₉ and the local genotype Pyrus pyraster L. Experiments were conducted during 2024-2025 under controlled in vitro conditions. Aseptic establishment of field-derived Pyrus pyraster explants was evaluated separately. Treatment with 0.2% mercuric chloride for 3.5 and 4 min resulted in the highest regeneration rates, reaching 69.84 ± 8.40% and 64.29 ± 7.14%, respectively. Culture medium formulation significantly affected the multiplication coefficient. The highest mean multiplication coefficient, 3.69 ± 0.25, was obtained on M3, which contained 75% of the standard mineral nitrogen concentration, 0.8 mg L⁻¹ 6-benzylaminopurine, 0.5 mg L⁻¹ gibberellic acid, and 0.1 mg L⁻¹ indole-3-butyric acid. M3 also produced the numerically greatest mean shoot length of 5.13 cm, although shoot-length observations were evaluated descriptively. Genotype-specific responses were likewise interpreted descriptively because genotype and genotype × medium effects were not statistically tested. Because several medium components varied simultaneously, the performance of M3 cannot be attributed to an individual component. M3 was therefore identified as the best-performing complete formulation and a candidate for further factorial evaluation and pilot-scale propagation of the evaluated pear rootstocks.