Effects of Pretreatment, Day Length and Temperature on Induction and Breaking of Dormancy in Strawberry Plants

Effects of pretreatment, growing temperature and day length on dormancy of strawberry plants were investigated. ‘Hoko-wase’ strawberry plants were pretreated with various day lengths in the glasshouse (minimum night temperature, 20°C) from October 21, 1981 to March 3, 1982. As the pretreatment, twenty plants each were grown under short day (natural day length), long day (16 hours) and long day+GA, respectively. Four plants were chosen from each pretreatment plot and transferred to the phytotron on March 3. Twelve plants each were cultivated at 15, 20 and 25°C in the phytotron under natural day length until September 22. Results were as follows.1. In the case of the higher growing temperature (25°>20°>15°C), dormancy was induced earlier and was also broken earlier in the short day pretreatment than in the long day and the long day+GA pretreatments.2. Judging from the elongation of petioles, we observed that the higher the growing temperature (25°>20°>15°C), the weaker the degree of dormancy becomes.3. In the case of the higher growing temperature (25°>20°>15°C), the elongation of petioles was observed even under the shorter day length condition and accordingly dormancy was broken a little earlier than expected.4. From these results, it is deduced that the lower the growing temperatures of 15, 20 and 25°C, the larger is the inductive effect toward dormancy. Furthermore, at the same growing temperature, short day has an inductive effect toward dormancy and long day has a breaking effect on dormancy.