Endophytes Bacillus amyloliquefaciens AW3 (CGMCC1.16683) improves the growth of Populus davidiana × Populus bolleana (PdPap) and induces its resistance to wilt disease by Fusarium oxysporum Fox68 (CFCC86068)

Populus davidiana × Populus bolleana (PdPap) root rot caused by Fusarium oxysporum is a major disease in China. Controlling this disease requires extensive use of chemicals. The use of plant endophytes, such as Bacillus, may be a suitable alternative to chemical agents. In this study, we isolated a strain of Bacillus amyloliquefaciens (AW3) by thermal stimulation and confrontation method from fleshy tap roots of Brassica rapa L. We then determined its inhibitory effect on the growth of F. oxysporum (Fox68) and how it induces the disease resistance of PdPap. The confrontation area and roots were visualized using an optical microscope and a scanning electron microscope, respectively, and mycelial cell malformation, swelling, and distortion observed. AW3 and F. oxysporum were inoculated in a variety of combinations that reduced the disease level. PdPap defense-related enzymes, such as PAL, PPO, SOD, and CAT, increased significantly. Besides, several genes associated with plant defense and hormonal signal transduction were highly expressed. Under the biological stress of Fox68, AW3 directly acted on the hyphae of Fox68, reducing the infection of PdPap by Fox68 and promoting PdPap growth. AW3 also induced the accumulation of defense-related enzymes/genes that conferred resistance. Therefore, AW3 could serve as a bio-control agent of wilt disease caused by F. oxysporum in PdPap.