Colonization of Endophytic Bacillus velezensis BHZ-29 in Cotton and Its Induction of Resistance to Cotton Verticillium Wilt

Cotton Verticillium wilt is a devastating fungal disease caused by Verticillium dahliae, and biological control has become a safe and efficient strategy for its green prevention and control. In this study, the endophytic strain Bacillus velezensis BHZ-29 was used as the biocontrol material, and rifampicin labeling and greenhouse pot assays were performed to clarify its colonization characteristics and induced disease resistance mechanism in cotton. The results showed that the rifampicin-resistant mutant strain maintained consistent morphological traits, antagonistic activity and biocontrol performance with the wild-type strain, ensuring the reliability of colonization tracing. Strain BHZ-29 could stably colonize the roots, stems and leaves of different cotton varieties, with roots serving as the dominant colonization tissue. Physiological analysis indicated that BHZ-29 inoculation significantly activated the antioxidant and defense enzyme system of cotton, including POD, CAT, SOD, PPO and PAL. The defense enzyme activities of cotton leaves showed a trend of first increasing and then decreasing, and the combined inoculation of BHZ-29 and V. dahliae exhibited the highest enzyme activity. Meanwhile, BHZ-29 treatment significantly increased vitamin C content and reduced malondialdehyde accumulation in cotton, alleviating pathogen-induced oxidative damage. Field pot verification confirmed that BHZ-29 possessed excellent and broad-spectrum biocontrol effects on cotton Verticillium wilt with stable control efficacy across different cotton varieties. This study clarifies the colonization and induced resistance mechanism of strain BHZ-29 against Verticillium wilt, providing a promising microbial resource and theoretical basis for the green biological control of cotton soil-borne diseases.