A two-in-one molybdenum disulfide-chitosan nanoparticles system for activating plant defense mechanisms and reactive oxygen species to treat Citrus Huanglongbing.

Citrus Huanglongbing (HLB) poses an enormous challenge to Citrus cultivation worldwide, necessitating groundbreaking interventions beyond conventional pharmaceutical methods. In this study, we propose molybdenum disulfide-chitosan nanoparticles (MoS-CS NPs) through electrostatic adsorption, preserving the plant-beneficial properties of molybdenum disulfide (MoS), while enhancing its antibacterial effectiveness through chitosan modification. MoS-CS NPs exhibited significant antibacterial efficacy against RM1021, and the closest relatives to Candidatus Liberibacter asiaticus (CLas), Erwinia carotovora, and Xanthomonas citri achieved survival rates of 7.40 % ± 1.74 %, 8.94 % ± 1.40 %, and 6.41 % ± 0.56 %, respectively. In vivo results showed, CLas survival rate of 10.42 % ± 3.51 %. Furthermore, treatment with MoS-CS NPs resulted in an increase in chlorophyll and carotenoid content. Concomitantly, a significant reduction in malondialdehyde (MDA), soluble sugar, hydrogen peroxide (HO), and starch contents was also observed. Mechanistically, MoS-CS NPs enhanced the activity of antioxidant-related enzymes by upregulating the expression of antioxidant genes, thereby galvanizing the antioxidant system to alleviate oxidative stress. Collectively, this dual functionality-combining direct antibacterial action with the activation of plant defense mechanisms-marks a promising strategy for managing Citrus Huanglongbing and suggests potential agricultural applications for MoS-based antibacterial treatments.