カブの花房形成に及ぼす低温処理期間と低温処理後の日長の影響

Abstract

Effects of vernalization and subsequent photoperiod on inflorescence formation in turnip (Brassica rapa L.) were investigated. 1. 'Hikari' plants were exposed to 9°C for 0, 1, 2, and 3 weeks and then grown under 8-, 12-, 16-, and 24-hr photoperiods. The percentage of plants with terminal inflorescences and the number of lateral inflorescences per plant increased, whereas the number of nodes below the terminal inflorescence decreased as the chilling duration and the subsequent photoperiods were lengthened. However, 90% of unvernalized plants formed terminal inflorescence when grown under constant light, whereas in plants vernalized for 3 weeks, the percentage of plants with a terminal inflorescence did not differ between those under 12- and 24-hr photoperiods, and number of nodes below the terminal inflorescence were similar in plants exposed to 8- to 16-hr photoperiod. The number of lateral inflorescences per plant under the 8- to 16-hr day did not differ. 2. When 'Narusawana' plants were grown under the same conditions as 'Hikari', the responses were similar ; i.e., the percentage of plants with a terminal inflorescence and number of lateral inflorescences per plant increased as the chilling duration and the subsequent photoperiods were lengthened. When plants were kept at 9°C for 3 weeks under 12- to 24-hr photoperiods, no differences were found in the number of nodes below the terminal inflorescence. The number of lateral inflorescences per plant exposed to 8- to 16-hr photoperiods were also similar. 3. We proposed the following index to express the effects of vernalization and photoperiods on the inflorescence formation of turnip plants : Flower formation index (%)=Percentage of plants with a terminal inflorescence (%)×(Number of lateral inflorescences per plant+1)/(Number of nodes below the terminal inflorescence+1) Terminal inflorescence is calculated as one node. When this formula was applied to the results of this experiment, effects of the vernalization and photoperiods on the inflorescence formation in 'Hikari' and 'Narusawana' were more precise.