Effects of hormones, carbon sources, and photoperiod on bulblet development in Lilium fargesii Franch during in vitro culture

Lilium fargesii Franch is a slow-growing species endemic to China with small-sized bulbs; however, the factors affecting bulblet enlargement remain unclear. Here, we show that 60 g·L^− 1 sucrose and darkness are optimal conditions to increase the weight and expansion of bulblets. Both the weight gain and expansion rates of bulblets were further promoted by exogenous indole-3-butyric acid (IBA), the gibberellin (GA) inhibitor paclobutrazol (PBZ), and the jasmonic acid (JA) inhibitor diethyldithiocarbamic acid (DIECA), and were inhibited by exogenous benzylaminopurine (6-BAP) and methyl jasmonate (MeJA) under a 16-h light/8-h dark photoperiod. Exogenous application of GA₃, 6-BAP, and MeJA, but not IBA, increased internal hormone contents; the inhibitors kynurenine (Kyn), PBZ, and DIECA decreased internal hormone levels, whereas the cytokinin inhibitor lovastatin had no effect. The weight gain and expansion rates of bulblets were promoted by high internal IBA and 6-BAP contents and low internal MeJA content. The roots number of bulblets was promoted by decreased IBA and increased GA₃, and was inhibited by increased IBA and deceased 6-BAP. Endogenous GA₃ or 6-BAP levels influenced the proliferation and total weight of daughter bulblets but not the formation of new leaves. Bulblets enlargement was positively associated with the proliferation and total weight of daughter bulblets and negatively associated with internal MeJA content. The number of new leaves was significantly negatively correlated with the weight gain, expansion, and roots of bulblets. These findings provide valuable insights for the in vitro preservation of L. fargesii to facilitate the protection and utilization of wild germplasm resources.