Optimization of in vitro pollen germination and pollen viability testing in Bombax ceiba

Bombax ceiba has high ornamental, ecological, and economic values. In recent years, the kapok fiber obtained from B. ceiba fruits has become a research hotspot. Pollen morphology and viability are critical for kapok fiber yield; thus, we aimed to complete the palynological information of B. ceiba , determine the optimal conditions for in vitro germination, and obtain a method for assessing the viability of B. ceiba pollen by staining. B. ceiba pollen grains are oblate, with an average diameter of 40.16 ± 2.00 μm, with 3-colporate and reticulate pollen surface sculptures. For germination tests through single-factor and orthogonal experiments, the most effective conditions for in vitro B. ceiba pollen germination include 50 g/L sucrose, 0.2 g/L boric acid(H 3 BO 3 ), 0.2 g/L calcium chloride(CaCl 2 ), and 10 g/L polyethylene glycol 1500 (PEG-1500), at 30 °C. 2,3,5-triphenyl tetrazolium chloride(TTC) and 2,5-diphenyl monotetrazolium bromide (MTT) can effectively distinguish viable from unviable B. ceiba pollen. Evaluating the staining methods revealed a linear relationship between MTT staining and pollen germination; however, in the assessment of low-vitality pollen, the MTT staining significantly higher values compared to the pollen germination. This study has identified optimal media and a method to estimate B. ceiba pollen viability.