A tale of light and rot: UV-C light induces defence flavonols against Botrytis cinerea

Norwegian strawberry farms are utilising robotic deployment of UV-C light, leveraging its germicidal properties against a variety of fungal pathogens. Low doses of UV-C light are administered regularly throughout the growing season (up to 26 times before harvest), eliminating the need for fungicides. While low doses of UV-C suppress and delay germination of Botrytis cinerea spores, our findings show that these doses are not lethal. The near complete suppression of B. cinerea cannot be explained purely by repeated sublethal doses of UV-C. We hypothesise that UV-C treatment to control grey mould is concurrently inducing an unintended yet advantageous outcome: enhanced immunity in strawberry fruit through priming. Given that UV-C light serves as a mild stressor, we show how farm-level treatment with UV-C light significantly increases kaempferol-based flavonol in strawberry fruit, thereby increasing innate defence compounds. We further confirmed the antimicrobial role of kaempferol by measuring the minimum effective concentration wherein B. cinerea growth is halted at the tip of the emerging hyphae. These results indicate a potential priming effect by UV-C light specifically enhancing flavonol defence compounds. This collaborative effort underscores the hitherto unexplored potential of UV-C technology in Nordic agriculture.