Hexyl Gallate Loaded Microgels Enable Efficient Protection Against Citrus Canker

The development of efficient and environmentally friendly plant protection systems is one of the major challenges for a sustainable agriculture of the future. Citrus canker caused by the pathogen Xanthomonas citri subsp. citri (X. citri) affects all cultivated citrus species worldwide and is responsible for enormous economic losses and restrictions in international trade. Currently used commercial copper-based formulations are the origin of contamination for soil and groundwater, affecting local ecosystems and human health. A copper-free sustainable microgel-based plant protection system able to efficiently combat X. citri is developed. Microgels decorated with anchor peptides exhibit strong non-covalent attachment to the surface of orange leaves and have the ability to release hexyl gallate, which inhibits the growth and spreading of pathogens. The tailored design of the microgel network allows high loadings of hexyl gallate (up to 40 wt.%) and a controlled release of gallates from microgels that provide long-term protection. The antibacterial activity of the hexyl gallate-loaded microgels is demonstrated by various in vitro assays as well as on orange plants in greenhouse settings. The experimental results suggest that the developed sustainable microgel-based plant protection system for citrus trees allows efficient abatement of X. citri and reduces environmental pollution caused by copper formulations.