Simple SummaryThe study found thatBacillus velezensisHN-Q-8 has an antagonistic effect onAlternaria solani. After being pretreated with strain HN-Q-8, which can induce potato plant resistance to early blight by regulating defensive enzyme activities and trig-gering the JA/ET pathway, as well as promote growth by regulating the contents of indole acetic acid, gibberellic acid 3 and abscisic acid, enhancing the chlorophyll content, and stimulating root activity. In addition, live bacteria and secondary metabolites should be used together for the best results. Thus,B. velezensisHN-Q-8 strain is an effective bacterial biocontrol agent, and our study can provide vital information for the research and development of biocontrol bacteria.AbstractBacillus velezensisHN-Q-8, isolated in our previous study, has an antagonistic effect onAlternaria solani. After being pretreated with a fermentation liquid with HN-Q-8 bacterial cell suspensions, the potato leaves inoculated withA. solanidisplayed smaller lesion areas and less yellowing than the controls. Interestingly, the activity levels of superoxide dismutase, peroxidase, and catalase in potato seedlings were enhanced by the addition of the fermentation liquid with bacterial cells. Additionally, the overexpression of key genes related to induced resistance in the Jasmonate/Ethylene pathway was activated by the addition of the fermentation liquid, suggesting that the HN-Q-8 strain induced resistance to potato early blight. In addition, our laboratory and field experiments showed that the HN-Q-8 strain can promote potato seedling growth and significantly increase tuber yield. The root activity and chlorophyll content of potato seedlings were significantly increased along with the levels of indole acetic acid, gibberellic acid 3, and abscisic acid upon addition of the HN-Q-8 strain. The fermentation liquid with bacterial cells was more efficient in inducing disease resistance and promoting growth than bacterial cell suspensions alone or the fermentation liquid without bacterial cells. Thus, theB. velezensisHN-Q-8 strain is an effective bacterial biocontrol agent, augmenting the options available for potato cultivation.