Polygonatum cyrtonema Hua endophytic bacterium Bacillus amyloliquefaciens HJ9 and its degenerate strain dHJ9: Antifungal activity and mechanisms

To control Fusarium -induced root rot in Polygonatum cyrtonema Hua, the endophytic antagonistic bacterium against root rot was screened in this work. Furthermore, antifungal capacity and mechanisms of the obtained Bacillus amyloliquefaciens ( B. amyloliquefaciens ) HJ9 and its degenerate strain dHJ9 were investigated. The obtained data demonstrated that cell-free supernatant (CFS) of B. amyloliquefaciens HJ9 significantly inhibited mycelial growth, spore germination, and biofilm formation of Fusarium sp. F2, whereas CFS of B. amyloliquefaciens dHJ9 exhibited substantially diminished antagonistic activity. The antifungal mechanism studies indicated that B. amyloliquefaciens HJ9 primarily disrupted the cell membrane integrity of Fusarium sp. F2, evidenced by increased membrane damage indicators. Pot trials confirmed that B. amyloliquefaciens HJ9 CFS showed optimal root rot control, superior to bacterial suspensions, whereas B. amyloliquefaciens dHJ9 treatment even exacerbated the disease. The degeneration resulted not only in the lose of key biosynthetic gene clusters, but also in a pronounced reduction in the production of the plant growth substances like indole-3-acetic acid (IAA). This study established a foundation for developing biocontrol agents based on the bioactive metabolites of endophytes from P. cyrtonema Hua. • The biocontrol of Polygonatum sp. root rot using endophytes has been firstly reported. • The strain significantly inhibited mycelial growth, spore germination, and biofilm formation of Fusarium sp. F2. • The strain primarily disrupted the cell membrane integrity of Fusarium sp. F2, and thus showed strong antifungal activity. • The degenerate strain dHJ9 exhibited downregulation of the key lipopeptide gene clusters itu A and bam D.