Reusing wasted bioresources for crop protection: Calcinated oyster shell powder enhances rhizospheric microbial-mediated suppression of root-knot nematodes

The root-knot nematode (RKN) Meloidogyne incognita is one of the most destructive plant-parasitic nematodes (PPNs) affecting crop production worldwide. Our earlier study revealed that calcinated oyster shell powder (OSP) effectively suppressed tobacco RKN disease. However, the suppression mechanism of OSP against RKNs remain unknown. Our study revealed that calcinated OSP reduced the tobacco root-knot index by more than 38% by inhibiting the migration of second-stage juveniles of Meloidogyne incognita (J2) in the soil. Furthermore, OSP reduced the J2 density in the tobacco rhizosphere by 43.69% and significantly increased the soil pH by 0.68; moreover, OSP increased the contents of soil exchangeable calcium (ExchCa) and exchangeable magnesium (ExchMg) by more than 50%. Moreover, soil properties, including ExchMg, ExchCa and pH, enhanced the microbial-mediated suppression of J2. Specifically, Proteobacteria and Gemmatimonadota dominated the microbial community suppressing RKN, and fungal richness contributed to the suppression of RKNs; in addition, Chloroflexi and Acidobacteria dominated the microbial community promoting RKN prosperity. Our study revealed that the reuse of wasted oyster shell powder as an innovative antagonist is a promising avenue for ecofriendly RKN management strategies. IMPORTANCEThere is increased demand for ecofriendly RKN management strategies, and this study is the first to propose that the reuse of wasted oyster shell powder as an innovative antagonist against RKNs is effective, and calcinated oyster shell powder can reduce tobacco root-knot index and Meloidogyne incognita (J2) density by inhibiting the migration of J2s and enhancing the microbially mediated suppression of J2s in the tobacco rhizosphere. Moreover, several soil microbial and physicochemical indicators, including the contents of soil exchangeable calcium, exchangeable magnesium, pH and the relative abundance of Proteobacteria, Gemmatimonadota, Chloroflexi and Acidobacteria in plant rhizosphere were suggested to guide the development of ecofriendly PPN management strategies.