Field application of star polymer-delivered chitosan to amplify plant defense against potato late blight

The application of environmentally-friendly fungicides, such as elicitors and botanical fungicides, to minimize the risk of exposure to the ecosystem has become a global trend. However, the bioactivity and absorbency of elicitors are critical factors that limit the large-scale field application. With the objective of exploring a sustainable method for controlling plant diseases, a star polymer (SPc) was constructed to deliver plant elicitors/botanical fungicides with a low production cost. The SPc could be complexed with chitosan through hydrogen bond and Van der Waals forces. The complexation of SPc with chitosan decreased chitosan particle size from 144.61 nm to 17.40 nm in an aqueous solution. The SPc could activate the endocytosis pathway of plants by a nano-delivery system to amplify the defense responses induced by the chitosan elicitor. The nano-sized chitosan/SPc complexes exhibited enhanced control effects against potato late blight, which is considered one of the most destructive crop pathogens threatening global food security. Similar to chitosan, the eugenol could assemble with SPc through electrostatic interactions, and the toxicity of eugenol delivered by SPc was also improved against potato late blight. As an adjuvant, SPc could be applied to increase chitosan and eugenol’s control efficacies in the field. Here we report the first application of a nano-delivery system to improve plant defenses to the best of our knowledge. The SPc adjuvant’s application appears to be suitable for delivering plant elicitors/botanical fungicides, which is beneficial for improving bioactivity and decreasing the application quantity and frequency of conventional fungicides.