Acibenzolar-S-methyl activates stomatal-based defense against Pseudomonas cannabina pv. alisalensis in cabbage

Abstract

Pseudomonas cannabina pv. alisalensis (Pcal), which causes bacterial blight of brassicaceous plants, is an economically important pathogen worldwide. Copper fungicide and antibiotics are major strategies to manage the disease caused by Pcal; however, a Pcal strain resistant to these chemicals has already been found, and severe outbreaks of bacterial blight have been reported on cabbage in Japan. Therefore, there is an urgent need to develop new Pcal management strategies. Plant defense activators could be useful not only to protect plants against invading pathogens, but also to reduce the amount of copper fungicides and antibiotics applied. However, the mechanisms by which plant defense activators contribute to controlling diseases remains unclear. In this work, we focused on cabbage and acibenzolar-S-methyl (ASM), a well-known plant defense activator. Expression profiles revealed that ASM induced expression of systemic acquired resistance (SAR) marker genes including PR1, PR2, and PR5 in cabbage plants. We also demonstrated that a soil drench with ASM 2 h before transplanting clearly reduced bacterial blight symptoms and reduced Pcal bacterial populations in cabbage. ASM application was also able to prime cabbage for Pcal resistance by activating stomatal-based defense. Our findings highlight that ASM protects plants from bacterial pathogens by activating stomatal-based defense.