Crown-cooling Treatment Induces Earlier Flower Bud Differentiation of Strawberry under High Air Temperatures

Global warming is predicted to increase air temperatures. With the aim of ensuring future stable production of strawberry under high autumn air temperatures, we examined the effect of a crown-cooling treatment on flower bud differentiation, flowering characteristics and fruit yield in a June-bearing strawberry (Fragaria×ananassa Duch. cv. Fukuoka S6). We forced strawberries under high air temperature conditions (controlled day/night temperatures of 30/27°C) to simulate future global warming. For approximately 40 d after transplanting in August, strawberry crowns were cooled using a crown-cooling tube filled with water controlled to temperatures of 10, 15, 20 and 25°C. The crown-cooling treatments of 10, 15 and 20°C significantly (P‹0.05) promoted flower bud differentiation in the first inflorescence compared with controls. This earlier differentiation resulted in quicker anthesis, and led to an increase in marketable fruit yield in December. However, continuous cooling treatments of 10 and 15°C after flower bud differentiation negatively affected anthesis and fruit yield. These data suggest that crown-cooling treatment for an appropriate period may be able to stabilize strawberry production under high air temperatures.