Dormancy relations and flowering of the strawberry cultivars Korona and Elsanta as influenced by photoperiod and temperature

Dormancy and flowering responses of the strawberry cultivars Korona and Elsanta have been studied in controlled environments. After short day (SD) floral induction for 5 weeks at temperatures ranging from 9 to 27 °C, long photoperiods only were required for optimal leaf and inflorescence growth and development at 18 °C, with no additional effect of chilling. However, with extended SD treatment for 10 or 15 weeks at 15 °C the plants entered the usual semi-dormant state typical for strawberry plants in late autumn, and subsequent long day (LD) conditions could not fully reverse the restrained growth habit. Extended SD treatment at 6 °C did not bring about this dormant state, indicating that the dormancy-inducing effect of SD is continuously nullified by such low temperature. When SD induced plants were forced under continued SD conditions, leaf and inflorescence growth were strongly restrained even in plants that had been chilled for up to 6 weeks. The restrained plant growth habit attained in SD, proved not to be a reliable indicator of the dormant state of the plants as it occurred also at low temperature. Floral induction in ‘Korona’ and ‘Elsanta’ was shown to have an obligatory SD requirement at temperatures ranging from 9 to 21 °C, while SD floral induction was marginal at 27 °C. The floral inducing effect of SD was also strongly reduced at temperatures below 9 °C. Application of these findings for multiple cropping of inherently single-cropping strawberry cultivars in winter season greenhouse production systems is discussed.