Seed coating with biocontrol bacteria encapsulated in sporopollenin exine capsules for the control of soil-borne plant diseases

Coating seeds with biocontrol agents represents an effective approach for managing soil-borne plant diseases. However, improving the viability of biocontrol microorganisms on the seed surface or in the rhizosphere remains a big challenge due to biotic and abiotic stresses. In this work, we developed a microbial seed coating strategy that uses sporopollenin exine capsules (SECs) as carriers for the encapsulation of the biofilm-like biocontrol bacteria. SECs was extracted from camellia bee pollen, and then characterized by Fourier Transform infrared spectroscopy (FTIR), elemental analysis and thermal gravity analysis (TG). The Paenibacillus polymyxa ZF129, a biocontrol bacterium, was introduced into SECs using the vacuum-incubation method and characterized by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Notably, the ZF129 cell formed a biofilm-like structure inside the SECs, which enhanced their tolerance to acidic stress. As a proof of concept, we applied ZF129-loaded SECs to coat pak choi seeds using a straightforward plate-shaking technique. The coated seeds demonstrated a high control efficacy of up to 60.46 % against clubroot disease. Overall, this study sheds light on the application of SECs as promising carrier for the encapsulation of biofilm-like biocontrol bacteria, further augmenting the biocontrol functionality of microbial seed coating.