Biocontrol effects of three antagonistic bacteria strains against Codonopsis pilosula wilt disease caused by Fusarium oxysporum

Codonopsis pilosula wilt disease caused by Fusarium oxysporum poses a serious threat to the commercial quality and yield of C. pilosilua crops in China. In this study, three selected isolates of antagonistic bacteria, Paenibacillus polymyxa YF, Bacillus amyliquefaciens HT, and Bacillus velezensis BQ, were evaluated for their potential ability to control C. pilosula wilt disease. All three strains could colonize the roots of C. pilosula. However, strain BQ had the strongest colonization ability, in that its colonization abundance was stable at 5.2 x 10(3) CFU/g. Pot experiments showed that each of these three strains may contribute to enhancing C. pilosula's growth in terms of its plant height, root length, root fresh weight, and root dry weight. All three antagonistic strains were able to effectively suppress the mycelial growth of F. oxysporum by 45 % to 65 %, with strain YF outperforming the other two strains. Similarly, 1 % sterile supernatant filtrate of each strain was capable of reducing by 40 %similar to 50 % the germination of F. oxysporum conidia. Pot experiments also demonstrated that strain YF was best able to ameliorate symptoms of C. pilosula wilt disease, whereas strain BQ was best able to prevent them. Similar results were obtained from ex vivo experiments, in that the strain YF was superior to the other two strains to ameliorate symptoms, while strain BQ was superior to the other two strains to prevent them. Analysis of resistance enzyme activity revealed that both peroxidase (POD) and phenylalanine ammonia-lyase (PAL) in C. pilosula roots increased significantly, by 4.5-4.7 and 1.7-1.9 times, in response to the three bacterial strain treatments. And resistance enzyme activity of all three bacterial strain treatments were significantly higher than F. oxysporum treatment and the co-treatment group (F. oxysporum + Antagonistic bacteria treatment groups).