Objective To clarify the cytological and physiological mechanism of the incompatibility of distant hybridization between peony species, and provide theoretical and experimental basis for distant hybridization of peony.

Method Using P. ostii ‘Feng Dan’ as the female parent and Paeonia baokangensis Z. L. Dai et T. Hong sp. Nov. as the male parent, the compatibility of distant hybridization and pollination was studied for exploring the relationship between the changes of pistils protect enzyme activity, soluble substance content and endogenous hormone content after pollination, pollens germination and pollen tubes growth.

Result The results showed that the cytology of Paeonia baokangensis Z. L. Dai et T. Hong sp. Nov. and P. ostii ‘Feng Dan’ distant hybridization was poor as a result of slow pollens germination, corpus callosum deposition in pollen tubes, severe twisting and entanglement, disordered growth and branching, and only part of the pollens could pass through the style to the ovary. After pollination, the rapid increase of SOD activity was beneficial to pollens stigma recognition and pollen tubes growth; The rapid increase of MDA content was not conducive to the elongation and growth of pollen tubes in distant hybridization; Distant hybrid pistils had higher soluble protein and soluble sugar content than selfed pistils, which is manifested by enhanced stigma recognition and pistils rejection; The content of IAA in selfed pistils was significantly higher than that of distant hybridization, high levels of IAA, GA₃ and IPA were helpful for pollens germination and pollen tubes growth; The ABA content of distant hybrid pistils was significantly higher than that of selfed pistils, high levels of ABA and JA showed an inhibitory effect on the growth of pollen tubes, induced the deposition of callosum, and the pollen tubes twisted and twisted to grow disorderly.

Conclusion Pre-fertilization barriers exist in distant hybridization of P. ostii ‘Feng Dan’ and Paeonia baokangensis, which is closely related to the changes of enzyme activity in the pistil, the dynamic changes of endogenous hormone content and the content of soluble substances.