Huanglongbing (HLB) is a severe disease in Citrus caused by Candidatus Liberibacter asiaticus (CLas) infection, which has brought about substantial economic losses in the global Citrus industry. Recently, HLB has been recognized as a plant immune-mediated disease resulting from the CLas-colonization stimulated immune responses and the excessive reactive oxygen species (ROS) accumulation in Citrus tissues. Here, we reported a manganese oxides nanozyme (MONPs) based strategy to scavenge and regulate the ROS metabolism in HLB infected Citrus, thereby protecting leaf tissues against oxidative stress. Transmission electron microscopy (TEM) imaging revealed that MONPs enable efficient delivery into intercellular space via spraying dispersion on the HLB leaves. ROS detection indicated the direct ROS scavenging ability of MONPs with high efficiency in HLB-Citrus about 60% ROS decreasing. Enzyme activation and gene expression analysis exhibited that the MONPs treatment could regulate ROS metabolism gene in Citrus to alleviate oxidative stress. Current research demonstrated that HLB-Citrus spraying with MONPs showed a noticeable protective effect within 22 days to alleviate the blotchy mottle symptoms. Furthermore, various physiological indexes of MDA, Starch, Total soluble sugar, Carotenoid and Chlorophyll in HLB-Citrus leaves exhibited significant improvement after MONPs post-treatment. This MONPs-based approach provides a promising alternative strategy to modulate and mitigate oxidative stress in HLB-Citrus serving for the Citrus industry.

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