Objective   Developments of flower buds and pollen grains, optimum medium for stamen callus induction, and proper conditions for seedling propagation and differentiation of Paeonia delavayi were investigated.

  Method  Dominant pollen grain development stages were examined under an optical microscope on the paraffin sections of red P. delavayi hard buds with visible color. On an MS solid medium, various plant growth regulators in different concentrations were added to determine the optimal formulation for the induction, proliferation, and differentiation of stamen callus.

  Result  (1) The prevailing stage of pollen grain development for the redP. delavayi, Y2-Y4, occurred in the mid-mononuclear period when the bud diameter was 10-17 mm but the color had yet to show. At T1-T2, the bud grew to a diameter ranging from 12 mm to 15 mm with less than 30% of the bud showing its color. That was in the single-core sideline period. When the diameter of a stamen reached 15-19 mm with a colored area greater than 30%, the T3-T4 stage was in the binuclear period. (2) The stamens were most effectively disinfected with running water for 30min followed by a rinse with 1% sodium hypochlorite for 8min. (3) The stamen could be optimally induced during the single-core sideline period. (4) The medium for optimal stamen callus induction was formulated with MS + 0.2 mg NAA·L⁻¹ + 0.5 g PVP·L⁻¹, and that for the proliferation MS + 0.5 mg NAA·L⁻¹ + 0.25 mg 6-BA·L⁻¹ + 0.5 mg GA₃·L⁻¹ + 1 g PVP·L⁻¹.

  Conclusion  This study clearly revealed the floral bud size, appearance, and dominant pollen grain development stages of the red P. delavayi and determined the optimal medium formulations and culture conditions for inducing, proliferating, and differentiating the stamen callus.