カブの花芽形成における温度と日長の相互作用に対する品種間差異

Abstract

The interactions between vernalization and photoperiodic effects on the flowering of 12 turnip varieties were examined under controlled environment. Seedlings of all varieties bolted and flowered under a long-day condition of 24 h day-length (LD) when the germinated seeds had been pre-exposed to low temperature at 3 °C (LT) for 30 days. Under the LD condition, the ratio of flower formation of all the varieties except for 'Tennoji' significantly decreased as the duration of LT treatment was shortened to less than 7 days. With LT treatment of more than 14 days, 80 to 100% of plants in all varieties formed flower buds under LD. When the seedlings were subjected to either LT and subsequently grown under a short-day condition of 8 h day-length (SD) or LD without LT treatment, the number of plants that formed flower buds substantially decreased. Furthermore, the effect of seed vernalization was counteracted by subsequent SD conditions under which the vernalized seedlings were grown throughout the experiment. Namely, flower formation and bolting of the vernalized seedlings were significantly inhibited when the LT-treated seedlings were subsequently grown under SD. These flowering responses of turnip plants to temperature and photoperiod significantly differed among the varieties used. We have classified the turnip varieties into five groups. 'Tennoji', 'Shogoin', and 'Hakatasuwari' strongly responded to the single treatment of either LD or LT, resulting in a high ratio of flower formation (Type I), whereas either treatment hardly induced the formation of flower bud in 'Yorii', 'Hinona', 'Ohnobeni', and 'Kanamachi' (Type II). 'Ohyabu', 'Ohmi', and 'Atsumi' showed an intermediate degree of flowering ratio between the Type I and II in repsonse to either LD or LT treatment (Type III). In 'Yamauchi', LD itself did not induce flower formation of non-vernalized plants, but the LT caused a high ratio of flower formation even under SD (Type IV). By contrast, 'Narusawana' showed a substantial ratio of flower formation due to LD without LT treatment, while the seedlings treated with LT did not flower under the following SD in this variety (Type V). Thus, the flowering of turnip plants is dramatically influenced by photoperiod as well as by temperature, and the responses to the two factors significantly differ among the varieties.