2003 Volume 72 Issue 4 Pages 329-334
The effects of high temperature interruption during low temperature treatment on inflorescence formation in turnip plants (Brassica rapa L. cv. Hikari) were investigated. Plants were exposed to 9°C (low temperature treatment) with interruptions of 17°C, 24°C or 30°C for 4, 6 or 8 hr per day. After the treatment, flower formation indices (%) were calculated. Based on these data, the total hours of vernalization, and hours of vernalization or devernalization per day were estimated. Flower formation indices were lower in the group of plants exposed to high temperature interruption than in the group of plants exposed to continuous low temperature. Moreover, the higher the interruptive temperature became and the longer its duration per day, the lower the flower formation index became. The indices were particularly low, when turnip plants were exposed to temperatures of 24°C or 30°C for 6 or 8 hr per day. The influence of high temperature interruption during the low temperature treatment was determined quantitatively by measuring the estimated hours of vernalization and devernalization per day. For example, vernalization effect of 9°C was diminished by 50 %, when the plants were exposed to 17°C for 8 hr per day during the low temperature treatment or to 24°C or 30°C for 4 hr per day during the low temperature treatment. Moreover, the vernalization effect of low temperature treatment was diminished by 90 % when plants were exposed to 24°C or 30°C for 8 hr per day during the 9°C treatment.
