June-bearing commercial strawberries (Fragaria ×ananassa) are preferable to everbearing ones for Japanese consumers due to their high quality. The June-bearing strawberry is typically a short day and low temperature (SDLT) type plant, and its harvesting time under natural conditions is from March to May or from November to May under a heating system during the winter. Autumn is the off-season, however, not only for consumers, but also confectionery makers who desire the June-bearing type in autumn. SDLT types can initiate flowering under 15 °C (or 17 °C) regardless of the photoperiod conditions, but inhibition of flowering occurs at high temperature (25 to 26 °C) conditions even under a short photoperiod (Bradford et al., 2010; Taylor, 2002; Verheul et al., 2006).
A super-forcing cultivation system has been developed in Japan for producing SDLT type strawberries from September to November (Yamasaki et al., 2003). The SDLT plants are grown in the field during daytime (average 31.2 °C), but they are placed into a curtained tunnel tent with air cooling (15 °C) from 1700 hr to 900 hr for 30–35 d to induce flower buds (Nakajima et al., 2014). As the system consumes a lot of energy, energy saving technology is strongly desired in Japan, especially after the Great East Japan Earthquake on 11 Mar. 2011.
Previously, we clarified that a reduction of FaTFL2 expression is a key signal for flowering in SDLT type commercial strawberries, and its expression seems to be regulated by temperature rather than photoperiod (Nakajima et al., 2014). In this study, we showed the reduction of FaTFL2 expression could be used as an indicator for flower initiation, and also demonstrated a new super-forcing cultivation system under a higher temperature condition than the previous condition, which leads to energy saving.
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