Dark interruption with red or blue LEDs mitigates powdery mildew and enhances bioactive compound accumulation in organically grown strawberries

Disease attack of powdery mildew (Podosphaera aphanis) is a major concern in organic strawberry production in tunnels or greenhouses production. We examined the impact of dark period interruption with light from blue and red LEDs on the occurrence of powdery mildew in organically grown strawberries, plant performance and on berry quality. Strawberry cultivars (Fragaria × ananassa cvs. Honeye and Faith) were grown in a climate chamber for two months in pots filled with peat based growing media certified for organic production. The plants were drip irrigated and fertilized with liquid organic fertilizers. They were exposed to a control treatment with 18 h light using white (polychromatic) LEDs and 6 h darkness or with treatments involving white LED treatment for 14 h, followed by darkness, interrupted after 2 h by 4 h of monochromatic blue or red LED exposure and additional 4 h of darkness. A three-factorial experiment including strawberry cultivars, light regimes and pathogen inoculation was performed using six replicates (pots) per cultivar and treatment. Light regime influenced the biomass of strawberry plants irrespective of cultivar, and dark period interruption with using red or blue LEDs promoted fresh biomass of the canopy and roots as compared to the control regime. Dark interruption using blue LEDs enhanced the accumulated berry yield, increased the antioxidant activities and reduced the disease incidence as compared to the control regime and the dark period interruption using red LEDs. Blue LED treatment favored the performance of the strawberry cultivars. The obtained results are of interest for organic strawberry production to be implemented in integrated control strategies for powdery mildew with potential to replace the use of pesticides and enhance product quality.