Reducing chill through night-break lighting and gibberellic acid application to achieve year-round UK strawberry production

Year-round production of strawberries is becoming increasingly important in the UK with heightened awareness of issues associated with climate change and national food security. So far, the UK strawberry growing season has been extended from six weeks in the 1980s to nine months (March-November). Despite this, strawberry imports have increased by 124% over the last 20 years to meet demand, largely during the winter. This highlights the need for further research into methods to enable production from December to February to support food security and sustainability of UK food production. A series of experiments was carried out to investigate the growing conditions for optimising winter glasshouse strawberry production. One key factor preventing early winter production of strawberries is their chill requirement. Hence, this series of experiments focussed on potential factors to supplement the amount of chill required to break dormancy and promote earlier flowering and fruiting. These factors included application of gibberellic acid (GA₃) and night-break lighting (NBL). The experiments were carried out in temperature-controlled glasshouse compartments in ambient lighting or with supplementary LED lighting and automatic photoperiod control. The plants were maintained under a constant 16-h day length and an initial 22/12°C day/night temperature regime which was reduced to 16/12°C prior to fruit-set. The experimental treatments consisted of one application of 50 ppm GA₃ versus a water control, application of 7 weeks of 10 W m^‑2 NBL for 15 min h^‑1 (10 pm-4 am) versus no NBL and an LED-lit versus ambient light environment. The greatest overall yield and Class 1% was produced in the LED-lit environment with NBL and no GA₃. Further analysis will pay particular attention to the optimal environmental manipulation methods for chill reduction to achieve the combined earliest and greatest fruit yield and quality for out-of-season glasshouse production.