Delayed degradation of tapetal cells causes the male sterility in Lagerstroemia speciosa 'Zichan'

• First detailed division of anther development in Lagerstroemia into 14 stages. • Delayed tapetal cell degradation identified as cause of male sterility in Lagerstroemia speciosa 'Zichan'. • Tapetal delay disrupts enzyme secretion, preventing timely microspore release. • Male sterility in Lagerstroemia speciosa 'Zichan' linked to abnormal expression of key callose genes. • Normal pollen wall development occurs despite abnormal microspore collapse. The degradation of tapetum and tetrad callose plays crucial roles in the development and maturation of microspores. Lagerstroemia speciosa 'Zichan' is a new cultivar of Lagerstroemia speciosa characterized by pollen sterility and continuous flowering. In this study, abnormal anther development with the delayed degradation of tapetal cells was identified in L. speciosa 'Zichan'. Cytological observation revealed that the degradation of the tapetal cells was delayed after tetrad formation. Histochemistry showed that callose persisted until the early unicellular stage. RT-qPCR analysis indicated that the expression of callose synthase genes was already abnormal at the microsporocyte stage, and the expression level of callose-degrading enzyme-related genes was abnormally low at the tetrad stage. RT-qPCR indicated that as early as the microsporocyte stage, the expression of callose synthase genes in L. speciosa 'Zichan' was already abnormal, and the expression of callose-degrading enzyme-related genes was lowest at the tetrad stage. Taken together, we hypothesize that the delayed degradation of tapetal cells inhibits the release of callose-degrading enzyme at the tetrad stage, further affecting the degradation of callose and microspore release at the right time, finally leading to microspore failure and male sterility in L. speciosa 'Zichan'.