Colonization by Klebsiella variicola FH-1 stimulates soybean growth and alleviates the stress of Sclerotinia sclerotiorum

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a destructive soil-borne disease leading to huge yield loss. We previously reported that Klebsiella variicola FH-1 could degrade atrazine herbicides, and the vegetative growth of atrazine-sensitive crops (i.e., soybean) was significantly increased in the FH-1-treated soil. Interestingly, we found that FH-1 could promote soybean growth and induce resistance to S. sclerotiorum. In our study, strain FH-1 could grow in a nitrogen-free environment, dissolve inorganic phosphorus and potassium, and produce indoleacetic acid and a siderophore. The results of pot experiments showed that K. variicola FH-1 promoted soybean plant development, substantially improving plant height, fresh weight, and root length, and induced resistance against S. sclerotiorum infection in soybean leaves. The area under the disease progression curve (AUDPC) for treatment with strain FH-1 was significantly lower than the control and was reduced by up to 42.2% within 48 h (P<0.001). Moreover, strain FH-1 rcovered the activities of catalase, superoxide dismutase, peroxidase, phenylalanine ammonia lyase, and polyphenol oxidase, which are involved in plant protection, and reduced malondialdehyde accumulation in the leaves. The mechanism of induction of resistance appeared to be primarily resulted from the enhancement of transcript levels of PR10, PR12, AOS, CHS, and PDF1.2 genes. The colonization of FH-1 on soybean root, determined using CLSM and SEM, revealed that FH-1 colonized soybean root surfaces, root hairs, and exodermis to form biofilms. In summary, K. variicola FH-1 exhibited the biological control potential by inducing resistance in soybean against S. sclerotiorum infection, providing new suggestions for green prevention and control.