Growth characteristics of somatic embryogenic cell- derived bulblets of an Oriental lily 'Casablanca' in greenhouse

Experiments have been carried out to determine the growth characteristics of somatic embryogenic cell-derived bulblets (EB) in greenhouse. Embryogenic cells were induced from the bulb scales of Lilium Oriental hybrid 'Casablanca' in MS agar medium supplemented with 2 mg L^‑1 picloram and 0.5 mg L^‑1 BA and proliferated in 5-L bioreactor. Micro bulblets were produced from the cells in a regeneration medium, solidified MS medium with 0.3% Gelrite. To determine an optimum period of low temperature storage, the EBs were stored at 4°C for different periods from 0 to 8 weeks with 2 weeks of intervals and planted in the raised bed filled with 8 cm depth of a soil mix for lily (Coco pit:peat moss:perlite = 7:2:1: Sing sung Co.) in greenhouse, and sprouting rates and plantlet growth were measured. EBs of various sizes in circumference were also compared for the sprouting and growth. Optimum plating dates and effect of summer harvest and low temperature storages were investigated in multiple cultivation trials, in which bulblets were planted either in January or March, and with or without low temperature storage during hot summer months (July, August). The EBs stored for seven and eight weeks at 4°C began to sprout 4 weeks after planting, which is faster than other treatments. The EBs, not treated with low temperature, sprouted mostly 16 weeks after planting with 75% of the highest sprouting rates. Since bulblets were planted and cultivated during winter months, the EBs stored less than 6 weeks in cold room were naturally exposed to the low temperature of greenhouse and sprouted as a consequence. Therefore, eight weeks of cold storage is the optimum for the sprouting of EBs and the rate of sprouting reaches up to 80%. In the experiments to determine the minimum size of EBs good for acclimatization cultivation, EBs of various sizes in circumference were planted and their growth was measured six months after planting. Highest ratio of sprouting (60%) was obtained in EBs larger than 30 mm and lower rates for smaller EBs, However, even the EBs smaller than 5 mm produced bulblets 4-6 cm in circumference and larger bulblets reached up to 8 cm, which indicates that EBs can be used as beginning materials like the bulblets produced traditionally from scale tissue cultures. In conclusion, the EBs are required to be stored 8 weeks at 4°C, and those as small as 15 mm in circumference can grow up to 6 cm bulblets in 6 months and 8 cm 10 months after planting. During the hot summer months, cold storage did not result in better growth of bulblets, compared to those without the summer cold storage. The results indicate that EBs can be an efficient propagation in proliferation compared to the bulblets produced traditionally from scale tissue culture.