Bacillus subtilis strain Ydj3 was applied to sweet peppers to understand the influence of this bacterium on the growth, fruit quality, and rhizosphere microbial composition of sweet pepper. The promotion of seed germination was observed for sweet pepper seeds treated with the Ydj3 strain, indicating that Ydj3 promoted seed germination and daily germination speed (131.5 ± 10.8 seeds/day) compared with the control (73.8 ± 2.5 seeds/day). Strain Ydj3 displayed chemotaxis toward root exudates from sweet pepper and could colonize the roots, which enhanced root hair growth. Following the one-per-month application of strain Ydj3 to sweet pepper grown in a commercial greenhouse, the yield, fruit weight, and vitamin C content significantly increased compared with those of the control. Additionally, the composition of the rhizosphere bacterial community of sweet pepper changed considerably, with the Bacillus genus becoming the most dominant bacterial genus in the treated group. These results suggested that B. subtilis Ydj3 promotes seed germination and enhances fruit quality, particularly the vitamin C content, of sweet pepper. These effects may be partly attributed to the B. subtilis Ydj3 colonization of sweet pepper roots due to Ydj3 chemotaxis toward root exudates, resulting in the modulation of the rhizosphere bacterial community.

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Background and Aims: Root-knot nematodes (Meloidogyne spp.) are endoparasitic plant pathogens. The infection seriously reduces the yield and quality of crops and frequently causes continuous cropping obstacles to facility cultivation. Biological control methods have been used to restrict root-knot nematodes, such as the application of crustacean shell powder, which is proposed to increase of chitinolytic bacteria, especially those belonging to Actinobacteriota. However, its influences to soil microbiome remain largely unknown. Methods: We used targeted metagenomics to investigate the changes in soil bacterial community for root-knot nematode-infected cucumber (Cucumis sativus L.) treated by crustacean shell powder with a pot system. Results: The chitin application significantly increased the relative abundances of Firmicutes and Actinobacteriota and reduced the symptoms caused by root-knot nematodes with a dose-dependent manner. Functional prediction suggested that these bacteria may improve chitin hydrolysis and nitrification in the soil, leading to inhibition of root-knot nematodes and growth promotion of cucumbers. On the contrary, the treatment of Streptomyces was less effective than the chitin application as they hardly colonize in the pot system. Conclusion: Chitin application may introduce chitinolytic bacteria and enhance soil nitrification to alleviate the infection of root-knot nematodes and stimulate plant growth.