March 2022
Horticultural Research (Japan)
Lily bulbs of Oriental hybrid ‘Casa Blanca’ produced in Hokkaido or Niigata were packed in polyethylene bags with wet peat moss and subjected to pre-chilling at various temperatures for various durations from 0 to 20 weeks before storing at –2.0°C. On moving to –2.0°C, bulbs were dissected and the shoot length and Brix of shoot tip juice were measured. Soluble carbohydrate concentrations of the shoot tip were analyzed by a conventional extraction method using hot ethanol with HPLC. After storage at –2.0°C for more than 7 months, they were grown in a glass house kept at a minimum temperature of 15°C to check for the occurrence of black shoots, non-flowering plants, and damaged leaves, which might be caused by long-term storage at –2.0°C. Rates of black shoots, non-flowered plants, and damaged leaves became high when bulbs were subjected to pre-chilling at 1°C for more than 12 weeks. The rise in rates and decrease of the sucrose content occurred simultaneously. Furthermore, changes in the sucrose content were closely related to changes of Brix. When bulbs were pre-chilled at 1, 6, 8, or 12°C for 8 weeks followed by 1°C for 10 weeks, those pre-chilled at 1 or 6°C showed a decreased sucrose content or Brix at the end of pre-chilling and higher rates of non-flowering plants and damaged leaves after storage at –2.0°C for 24 weeks. An extended duration of storage at –2.0°C for 8 weeks induced black shoots and non-flowering plants when bulbs were pre-chilled at 1°C for 18 weeks before moving to –2.0°C. From these results, it was concluded that excessively long pre-chilling of bulbs at low temperatures below 6°C induces black shoots and leaf damage after long-term storage at a subzero temperature.