Screening of a Bacillus Strain GXMZ-G3 Exhibiting Induced Systemic Resistance and Its Biocontrol Efficacy Against Banana Fusarium Wilt
YIN Dou-Dou1,*, SHEN Nai-Kun1,*, HUANG Xiao-Tian1, LUO Yan-Xin1, HUANG Yi-Hui1, LI Bao-Shen2, ZHANG Hong-Yan1,**
1 Guangxi Key Laboratory for Polysaccharide Materials and Modification/School of Marine Sciences and Biotechnology, Guangxi Minzu University, Nanning 530006, China; 2 Biotechnology Research Institute, Guangxi Academy of Agricultural Sciences, Nanning 530006, China
Abstract：Banana Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), represents a severe threat to global banana (Musa nana) cultivation industry. To develop environmentally sustainable strategies for managing this devastating disease, this study aimed to screen and characterize bacterial biocontrol agents capable of inducing systemic resistance in banana plants. Candidate strains were selected based on their ability to enhance the activity of key defense-related enzymes, including polyphenol oxidase (PPO), peroxidase (POD), and superoxide dismutase (SOD), in banana seedlings. The most promising strain was rigorously identified using integrated taxonomic approaches, encompassing morphological, physiological, and biochemical characterization, as well as phylogenetic analysis of the 16S rRNA gene sequence. Subsequently, its optimal culture conditions were systematically optimized. Antagonistic activity of the selected strain against Foc TR4 was evaluated through dual-culture plate assays and co-cultivation experiments with conidial suspensions to assess inhibition of mycelial growth and spore germination. Its capacity to induce systemic resistance in banana plants was further validated via root drench inoculation under controlled conditions. The results revealed that a single isolate, designated GXMZ-G3, was identified as Bacillus sp. This strain effectively induced systemic resistance in banana plants. In vitro assays demonstrated that GXMZ-G3 exhibited a 62.63% inhibition rate against Foc TR4 mycelial growth and suppressed conidial germination by 85.66%. Microscopic observation revealed severe morphological abnormalities in the inhibited Foc TR4 hyphae, including twisting, knotting, and fragmentation. Following root drench application of the GXMZ-G3 suspension, the activities of key defense-related enzymes (PPO, POD, and SOD) were elevated in banana leaves. Moreover, hydrogen peroxide (H2O2) accumulation and callose deposition were markedly enhanced in treated leaves. Jasmonic acid (JA) levels peaked at 0.48 ng/mL at 12 h post-inoculation, representing a 20.00% increase relative to the untreated control. In pot experiments, GXMZ-G3 achieved an 89.48% disease control efficacy against banana Fusarium wilt. In summary, the biocontrol strain GXMZ-G3 exerts a dual mode of action. It directly inhibited Foc TR4 hyphal growth and spore germination, while simultaneously priming systemic resistance in banana plants. These findings highlight GXMZ-G3 as a promising microbial resource for the biological control of banana Fusarium wilt disease.
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