The cross compatibility and endogenous hormone variation of distant hybridization between lagerstroemia indica and lythrum salicaria

• Varying degrees of pre-fertilization barriers exist in the reciprocal hybridization between L. indica ‘Fenjing’ and L. salicaria . • Spraying 250 mg·L⁻¹GA 3 solution was the potential way to prevent abscission of fruit in crossing L. indica and L. salicaria . • Insufficient IAA content and increased ABA and SA content may be the cause of abnormal embryonic development and excessive abscission of fruit. • Hybrid incompatibility responses involve marked changes in specific phytohormones including CKs, Auxin, JAs, ABA, and GAs. Distant hybridization, a widely utilized technique in plant breeding, can enhance the genetic diversity and integration of desirable traits. However, the presence of reproductive isolation often leads to incompatibility issues at various stages of hybridization. To elucidate the barriers and potential strategies for overcoming distant hybridization between Lagerstroemia indica and Lythrum salicaria , this study investigated pre-fertilization compatibility, the optimal concentrations of GA₃ and 6-BA solutions for fruit retention, and the dynamic changes in endogenous hormones within the ovary during different hybridization stages. Fluorescence microscopy analysis of pollen tube growth revealed distinct pre-fertilization barriers in reciprocal hybridizations between L. indica and L. salicaria , resulting in varying degrees of fruit abscission. Fruit retention experiments of L. indica × L. salicaria demonstrated that a 250 mg·L⁻¹ GA₃ solution was most effective in reducing fruit abscission, achieving a fruit-setting rate of 78 % by the 30th day post-pollination. Quantitative analysis of endogenous hormones using Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS) indicated that, on the first day post-pollination, insufficient IAA levels, coupled with elevated ABA and SA concentrations, may contribute to abnormal embryonic development and excessive fruit abscission. In contrast, following GA₃ treatment, IAA and GA₃ levels increased significantly, while ABA content decreased markedly on the first day post-pollination. Hybrid incompatibility responses involve marked changes in specific phytohormones including CKs, Auxin, JAs, ABA, and GAs. Notably, exogenous GA₃ application in cross pollination has shown efficacy in restoring these hormonal concentrations to levels comparable with those detected during self-pollination events. Cluster analysis further revealed that the concentrations of Auxin, GAs and CKs in the ovaries of the GA₃-treated hybrid pollination group exhibited significant variations at 1, 7, and 14 days after pollination.