Abstract
A study was carried out to develop a forcing culture of Japanese butterbur using one-year-old rootstocks ‘Haruibuki’ and ‘Mizubuki’ (the latter a native cultivar of Gunma pref.) with the objective of harvesting spikes between January and February and petioles in March. In the initial phase of this experiment, rootstocks with spikes were dug out in December, and kept in cold storage, then rootstocks with spikes were planted in a hotbed after removing them from the refrigerator in January, February and March. When rootstocks were immediately taken from the refrigerator, the color of bracts was too light for the spikes to be marketed. The color of bracts became deep green and the quality was improved by exposure to sunlight for six days after planting rootstocks in a greenhouse hotbed. When rootstocks were planted in March, spikes were loose since bracts were opened. When rootstocks were planted in a hotbed in January, it was possible to harvest S-size petioles (length: 40~50 cm) in March after harvesting spikes in January. It was thought that ‘Haruibuki’ was more suitable than ‘Mizubuki’ for forcing culture using one-year-old rootstocks, judging from the total spike and petiole yield.
