Development of an in vitro bulbil-induction system for Lilium lancifolium and the impact of exogenous auxin on bulbil formation

• A stable and reliable experimental platform were provided for bulbil formation study. • The histological process of bulbil formation in lily was described in detail. • The effects of auxin and its inhibitors on bulbil formation were studied. • A lower IAA/ZR ratio may be advantageous for bulbil initiation. Lilium lancifolium is one of the most widely cultivated lily species in China, valued for its ornamental, edible, and medicinal properties. Bulbils, which are specialized vegetative organs formed in the leaf axils of L. lancifolium , play a crucial role in its reproduction. However, the mechanisms underlying bulbil formation in L. lancifolium have not been elucidated. In this study, we established an efficient and stable in vitro induction system for bulbil formation using the bulbs of L. lancifolium sprouted at 4 °C as materials. Additionally, we systematically investigated the effects of exogenous auxins and auxin inhibitors on bulbil development through a combination of morphological and histological observations, as well as analyses of hormone levels and gene expression. The results indicated that low concentrations of exogenous IAA not only increased the number of bulbils formed per leaf axil but also reduced the time required for bulbil initiation. Conversely, auxin inhibitors suppressed this process, with 2,3,5-triiodobenzoic acid (TIBA) exhibiting the most pronounced inhibitory effect. Phytohormone analysis reviewed that auxin (IAA), cytokinin (ZRs) and gibberellin (GA3) may be involved in bulbil formation. Early auxin signaling is required for the initiation of axillary meristem formation during bulbil development, while the formation of bulbil primordia necessitates lower concentrations of auxin accumulation. Cytokinin appears to promote bulbil formation, and a lower IAA/ZR ratio may be advantageous for axillary meristem (AM) development. Gene expression data suggest that auxin- and cytokinin-related genes are implicated in bulbil initiation. The present study provided a viable system for investigating the mechanisms underlying bulbil formation in lilies. And the results laid solid foundation of the regulation of bulbil formation in plants.