Objective To elucidate the mechanism underlying female sterility in the new Lagerstroemia speciosa cultivar ‘Zichan’, and to provide a theoretical basis for the utilization and innovation of Lagerstroemia germplasm resources.

Method Histological analysis was employed to observe the morphological structure of embryo sac development in L. speciosa ‘Zichan’, and physiological and biochemical approaches were used to assess stigma receptivity, nutrient content and enzyme activity in flower buds.

Result In L. speciosa ‘Zichan’, the megaspore mother cells ceased embryo sac development after the formation of eight-nucleate embryo sac, accompanied by the degradation of egg cells and synergids. The embryo sac became vacuolated and eventually degenerated. In comparison with fertile L. speciosa, L. speciosa ‘Zichan’ flower buds accumulated lower levels of soluble sugars and starch at corresponding developmental stages, whereas the soluble protein content was higher during the mature embryo sac stage. At the eight-nucleate and embryo sac degradation stages, the superoxide dismutase (SOD) activity in L. speciosa ‘Zichan’ was significantly lower than that in L. speciosa by 66.14% and 40.20% respectively, the peroxidase (POD) activity was significantly higher by 139.20% and 348.65% respectively (P<0.05), and the catalase (CAT) activity showed a decreasing trend, opposite to that observed in L. speciosa.

Conclusion Female sterility in L. speciosa ‘Zichan’ is attributed to the degeneration and collapse of the embryo sac following the eight-nucleate formation stage. It is speculated that insufficient nutrient accumulation and abnormal antioxidant enzyme levels in flower buds may represent intrinsic sterility factors.