The Impact of Biocontrol Bacteria on  Cotton Resistance and Their Effects on Signaling Pathways Related to Defense Against Verticillium Wilt Infection

Abstract

This study prepared a mixed fermentation broth using two strains of Bacillus and investigated its inhibitory effects on the cotton Verticillium wilt pathogen, as well as its impact on the signaling pathways related to defense against Verticillium wilt infection in cotton.Biocontrol bacteria can effectively defend against plant diseases by competitively inhibiting pathogens and inducing plant immunity. Through plate confrontation assays, antimicrobial tests using mixed microbial fermentation broth and its dilutions, and their impacts on cotton seed germination, this study explores the defensive potential of the mixed fermentation broth.During the study, it was discovered that The mixed microbial fermentation broth could produce lipopeptide substances. The cotton's immunity against Verticillium wilt, following treatment with this broth, was assessed using DAB and trypan blue histological staining methods. Furthermore, the study involved monitoring the induced expression of resistance-related genes (PR1, PR5, NPR1), as well as the effects on the activities of defense-related enzymes in cotton (SOD, CAT, PPO, POD).The results indicate that The combination of two biocontrol bacterial strains exhibited a certain inhibitory effect on the cotton Verticillium wilt pathogen. Root drenching with the mixed fermentation broth significantly enhanced the transient burst of reactive oxygen species in cotton's defense signaling pathways, inducing an immune response. This response increased the sensitivity of cotton's hypersensitive response (HR), induced the expression of disease resistance-related genes, and heightened the activity of enzymes involved in reactive oxygen species scavenging, thereby enhancing systemic acquired resistance (SAR) in cotton. This study reveals that the mixed fermentation broth improved cotton's resistance to Verticillium wilt, significantly affecting the defense signaling pathways in response to the pathogen, with varying effects on induced resistance in different resistance genotypes of cotton.