A pH- and redox-stimulated responsive hollow mesoporous silica for triggered delivery of fungicides to control downy mildew of Luffa cylindrica.

Background: Downy mildew, a devastating disease of cucurbitaceous crops caused by Pseudoperonospora cubensis. Although a variety of fungicides are used to control downy mildew, choosing an effective product can be challenging. Environmental stimulus-responsive pesticide delivery systems have great potential to improve the effectiveness of disease and pest control and reduce the impact on environmentally beneficial organisms.

Results: In this work, a disulfide bond (SS)-modified and chitosan oligosaccharide (COS)-capped hollow mesoporous silica (HMS) pesticide delivery system was synthesized using a hard template method for the control of downy mildew in cucurbit crops. The synthesized nanoparticles were loaded with dimethomorph (DMM), denoted as DMM@HMS-SS-COS, and the developmental toxicity of these nanoparticles to zebrafish embryos were evaluated. The results showed that the prepared DMM@HMS-SS-COS exhibited excellent dual response properties to pH and glutathione (GSH), with an encapsulation rate of up to 24.36%. DMM@HMS-SS-COS has good ultraviolet (UV) radiation stability and adhesion properties. Compared with dimethomorph suspension concentrate (SC), DMM@HMS-SS-COS was more effective against downy mildew for up to 21 days. Toxicity tests showed that DMM@HMS-SS-COS significantly reduced the effect of DMM on the hatching rate and survival rate of zebrafish embryos.

Conclusions: This work not only demonstrates that DMM@HMS-SS-COS could be used as a nanodelivery system for intelligent control of downy mildew but also emphasizes the necessity of increasing the acute toxicity of nanoformulations to non-target organisms in environmental risk assessment. © 2022 Society of Chemical Industry.