Organic hydroponics induces systemic resistance against the air-borne pathogen, Botrytis cinerea (gray mould)

Here, we propose that organic hydroponics trigger induced systemic resistance (ISR) in lettuce against air-borne Botrytis cinerea, which causes gray mold. We compared effects of organic and chemical hydroponics, assessed presence of ISR elicitors in the hydroponic nutrient solution, and investigated molecular mechanism of ISR. Organic hydroponics significantly reduced gray mold lesions in lettuce (cultivated hydroponically) and cucumber (cultivated in soil and foliar sprayed with nutrient solution). The 1-aminocyclopropane-1-carboxylic acid synthase gene in lettuce and lipoxygenase and ethylene receptor-related gene in cucumber showed heightened expression, suggesting that the jasmonic acid/ethylene (JA/ET)-signaling pathway was involved in ISR for both crops. Low salicylic acid beta-glucoside levels confirmed role of the ISR signaling pathway. ISR in both lettuce and cucumbers indicated that elicitors in organic hydroponics were nonhost-specific and that the JA/ET pathway was activated without microbe-root interaction. Thus, organic hydroponics can be an effective method for both soil-borne and air-borne disease control.