Abstract
The state of inflorescence formation in turnip plants (Brassica rapa L.) cultiver ‘Taibyo-hikari’ was investigated to clarify the degree of vernalization by the “flower formation index”. First, germinated seeds were exposed to 0, 3, 6 and 9°C for 7–42 days under darkness. As a result, the index increased as the duration of low temperature lengthened in all plots. However, each plot at 3°C showed a highest index, which was 1.7–47.1% at 14–28 days of low temperature. The indices of 0 or 6°C plots were lower than that at 3°C. The lowest index was the percentage of 9°C which was 0–8.3%. Thus we thought that the most optimal temperature for vernalization was around 3°C. Second, the germinated seeds were exposed in the same way to 3°C for 14–35 days and then the seedlings were grown for 0–50 days under a short photoperiod (8 h at 20°C). As a result, the index decreased as the duration of the short photoperiod lengthened in all plots. However, each plot with a 50-day short photoperiod showed the lowest index. Thus, we thought that effort to promote vernalization was lost as the duration of short photoperiods lengthened, while suppression of vernalization was conversely maintained as the duration of low temperature lengthened.
