ABSTRACT Outbreaks of stem and root rot disease of sweet potato caused by Dickeya dadantii recently occurred in major sweet potato planting areas in China. This study aimed to screen effective Bacillus strains in biocontrol of the bacterial soft rot pathogen. We screened plant-associated Bacillus strains capable of inhibiting D. dadantii using an in vitro overlay culture assay and an in vivo tuber slice assay. All Bacillus strains inhibited D. dadantii growth and maceration of sweet potato tubers. Two strains B. amyloliquefaciens A3 and B. velezensis A2 showed significantly higher rates of in vitro inhibition (55% and 50%) on D. dadantii growth and in vivo reduction (82% and 77%) of the maceration of sweet potato tuber slices by D. dadantii than other Bacillus strains did. They showed broad-spectrum inhibition on growth of soft rot Dickeya and Pectobacterium strains. They protected sweet potato seed tubers from infection by D. dadantii and promoted seedling growth. Their culture supernatants inhibited D. dadantii growth, swimming and biofilms and damaged D. dadantii cells. B. amyloliquefaciens A3 is more effective than B. velezensis A2 in producing surfactins, well-known lipopeptide antibiotics and biosurfactants, and inhibiting D. dadantii. Together, we developed an effective method to screen effective Bacillus strains to control the soft rot pathogen D. dadantii and screened out a strong surfactin producer B. amyloliquefaciens A3, which can be used as a reference strain for further screening of more effective Bacillus strains and to develop an agent to control the stem and root rot disease of sweet potato.

中文翻译：

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甘薯茎根腐病病原菌Dickeya dadantii生防中芽孢杆菌菌株的筛选

摘要 近期我国主要甘薯种植区爆发了由Dickeya dadantii 引起的甘薯茎根腐病病。本研究旨在筛选对细菌性软腐病病原体进行生物防治的有效芽孢杆菌菌株。我们使用体外覆盖培养试验和体内块茎切片试验筛选了能够抑制 D. dadantii 的植物相关芽孢杆菌菌株。所有芽孢杆菌菌株均抑制 D. dadantii 生长和甘薯块茎的浸渍。两种菌株 B. amyloliquefaciens A3 和 B. velezensis A2 对 D. dadantii 生长的体外抑制率（55% 和 50%）和甘薯块茎切片浸渍的体内减少（82% 和 77%）显示出显着更高的比率由 D. dadantii 比其他芽孢杆菌菌株所做的。它们对软腐病 Dickeya 和 Pectobacterium 菌株的生长表现出广谱抑制作用。他们保护甘薯种子块茎免受 D. dadantii 感染并促进幼苗生长。他们的培养上清液抑制了 D. dadantii 的生长、游泳和生物膜，并破坏了 D. dadantii 细胞。B. amyloliquefaciens A3 在产生表面活性素、众所周知的脂肽抗生素和生物表面活性剂以及抑制 D. dadantii 方面比 B. velezensis A2 更有效。我们共同开发了一种有效的方法来筛选控制软腐病病原体 D. dadantii 的有效芽孢杆菌菌株，并筛选出强表面活性素生产者 B. amyloliquefaciens A3，可作为参考菌株进一步筛选更有效的芽孢杆菌菌株和研制一种防治甘薯茎根腐烂病的药剂。