High-frequency plantlet regeneration by somatic embryogenesis from mature zygotic embryos of onion

Somatic embryogenesis is a promising approach for plantlet regeneration. In order to establish a high-frequency plantlet regeneration system of onion in vitro, we used mature zygotic embryos as experimental material to improve the culture protocol. The results showed the highest induction rate of embryogenic callus (91%) was found when the NH4+/NO3- ratio in Murashige and Skoog (MS) medium was adjusted to 30/30 mM/mM. Well-proliferated embryogenic calli were observed in a 3 L airlift balloon-type bioreactor. During bioreactor culture, the continuous immersion culture was better. Inoculation density of 5 g/L and 0.1 vvm (air volume/culture medium volume per min) air volume were optimal for embryogenic callus proliferation. In addition, to obtain mature somatic embryos, the effects of sucrose and thiamine (V-B1) were examined. Results showed that 20 g/L sucrose favoured somatic embryo maturation. When the V-B1 concentration in normal MS medium (0.1 mg/L) was increased to 10 mg/L, the rate of somatic embryo germination reached 93.3%. When the mature somatic embryos were inoculated in MS medium without plant growth regulators, whole plantlets regenerated after 15 d of culture. During plantlet acclimatisation, the maximum survival rate (93.8%) was found in the substrate of 1/2 vermiculite and 1/2 perlite.