2020 年 64 巻 3 号 p. 107-112
Mustard (Brassica juncea L.) is an important vegetable worldwide. Its floral initiation has been reported to be related to the basic vegetative growth phase, a low-temperature, and a long-day requirements. Late flowering is required for year-round production when mustard is cultivated as a leaf vegetable, but many aspects of the flowering response are unclear. Herein, we investigated the responses of mustard genetic resources, collected from a tropical and/or sub tropical area of Myanmar under natural conditions, grown in an experimental field and under different temperature and day-length conditions, controlled by a phytotron. A total of 22 accessions from Myanmar were grown in a field in Tokyo, and the earliest accessions, M39 and M109, bolted at 38 days, M116 bolted at 71 days. The number of days from sowing to bolting varied widely among the accessions, up to 33 days. Regarding low-temperature requirements, we classified the accessions into three types: low requirement for low temperature (M44), high requirement for low temperature (M15), and neutral requirement for low temperatures (M36, M42, M96, P1). We observed that accessions J1, P2, M15, M36, M42, M44, and M96 could bolt without low temperature under certain long-day conditions. Conversely, we observed that J2 was a very late-maturing cultivar that did not bolt without low temperature even under long-day conditions．The critical day length of M15, M36, M42, M44, M96, J1 and P2 was estimated to be approx. 12 hr.
