Re-examination on the role of vernalization and photoperiod in the flowering of Brassica crops under controlled environment.

Flowering response of 7 cultivars belonging to 3 different varieties of Brassica campestris were explored in their relation to vernalization, photoperiod and gibberellins (GAs) under controlled environment using growth cabinets. In 5 Japanese cultivars (Nozawana, Uzuki-Komatsuna, Shin-Santosai, Bansei-Mana and Shigatsu-Shirona) out of 7 ones tested, flowering did not occur under 8hour photoperiods even though they had been vernalized (20 days) and received GA3 although it induced stem elongation. In those cultivars GAs are likely to play a direct role in the bolting but probably are not directly functional in initiating flowering. Two Chinese cultivars tested here were unique for their flowering responses. Tsai Hsin was a day neutral cultivar wlth low vernalization requirement ; it flowered either under 24 and 8hour photoperiods in both of vernalized and nonvernalized plants. Hong Tsai Tai was a typical long-day plant and it did not require vernalization under 24hour photoperiod. On the other hand, vernalization substituted the long-day requirement since seed-vernalized plants flowered even under short-days. Application of GA3 induced the flowering in nonvernalized plants under 8hour photoperiod and that of Ancymidol, an inhibitor of GA biosynthesis, inhibited the flowering of vernalized plants. In this cultivar, GAS Seem to play some role not only in the bolting but also in the ffowering itself.