Browning is prevalent in tissue cultures of Paeonia lactiflora Pall. (herbaceous peony), and severely affects and restricts the growth and differentiation of the explants. In this study, dipping excised explants in a sodium chloride (NaCl) solution as a pretreatment, adding polyvinyl pyrrolidone (PVP) to the culture medium, storing planted explants at 4 °C for 24 h, and transferring planted explants to a new medium after 24 h were considered as browning-suppression methods in tissue cultures of herbaceous peony ‘Festival Maxima’. The treated petal explants were cultured in a culture room with a 16-hour photoperiod, 25 °C temperature, and 80% relative humidity in darkness for 4 to 8 weeks. The results demonstrated that dipping excised explants in a 0.5 g·L⁻¹ NaCl solution, adding 0.5 g·L⁻¹ PVP to the medium, storing planted explants at 4 °C for 24 h, and transferring planted explants to the same fresh medium after 24 h could effectively inhibit browning. Adding PVP to the medium led to the greatest browning suppression percentage of 95%. Storing planted explants at 4 °C for 24 h reduced the effectiveness of other treatments in suppressing browning. After 8 weeks, dipping excised explants in a NaCl solution resulted in the highest callus induction percentage of 75%, while storing explants at 4 °C for 24 h suppressed callus formation. It was observed in all treatments that decreases in browning was accompanied with higher levels of phenols and lower activities of phenylalanine ammonia-lyase (PAL) and polyphenoloxidase (PPO). Overall, the results suggest that dipping in a NaCl solution was effective in alleviating the browning issues of herbaceous peony tissue cultures, and had positive synergistic effects with PVP on browning suppression and callus induction.

The effects of silicon (Si) on root development, mineral content, and expression of Si transporter genes in Euphorbia pulcherrima Willd. ‘Flame’, ‘Mable Bell’, ‘Green Star’, ‘Pink Bell’, and ‘Peach Bowl’ cultivars were investigated in this study. Stem cuttings in a propagation bench were drenched regularly with a solution containing either 0 (control) or 50 ppm of silicon (Si treatment) from potassium silicate (K₂SiO₃), with a 25 °C mean air temperature and 80% relative humidity (RH) under 70% shading. The results showed that the ‘Flame’ treated with Si had a significantly higher survival ratio as compared with that of the control (P ≤ 0.05) and that the Si treatment improved number of roots, length of longest root, fresh root weight, and dry root weight in all cultivars except ‘Mable Bell’. Supplementary Si increased the content of magnesium (Mg) and decreased the content of boron (B) and zinc (Zn) in the roots. The content of sulfur (S) in the shoots was increased by supplementary Si. The relative expression of Lsi1 and Lsi2 was higher in ‘Peach Bowl’, while it was lower in ‘Mable Bell’ and ‘Green Star’, which may be caused by the differing accumulation of Si in the shoot. Overall, supplementary Si had beneficial effects during cutting propagation of poinsettia cultivars, although these effects were cultivar-dependent.