Biocontrol potential of an artificial synthetic bacterial consortium against peony root rot disease

Tree peony (Paeonia suffruticosa), a traditional Chinese cultivated flowering shrub and a prominent landscaping plant, is subject to root rot. The key symptoms of root rot include black roots and the yellowing of leaves. Biological control is an effective and eco-friendly strategy for managing this disease. This study focused on the isolation, identification, and biological control of the pathogens causing peony root rot. Utilizing tissue isolation, pathogenicity determination, and rDNA-ITS sequence analysis, Fusarium solani and Fusarium oxysporum were determined to be the primary causal agents of peony root rot. Illumina MiSeq high-throughput sequencing of 16 s-rDNA was used to investigate and characterize bacterial community structure and diversity in healthy and diseased peony roots, rhizosphere, and bulk soil. Results indicated that the presence of pathogenic fungi influences the structure of the rhizosphere bacterial community and that peony roots exhibit a strong selective effect on root bacterial colonization. Variations in the composition of the endophytic microbial community in healthy and diseased roots exceeded the variation in the rhizosphere. Proteobacteria and Actinobacteria are the dominant taxa in the rhizosphere and among root endophytes, comprising 90–96 % of the bacterial microbiota. The rhizosphere of healthy plants exhibits a significant enrichment in Proteobacteria (79.6 %) and Actinobacteria (14.9 %), while root endophytes in healthy plats exhibit enrichment in Proteobacteria (83.5 %). In contrast, the rhizosphere and root endophytes in diseased plants are abundant in Proteobacteria (69 % and 66.1 %, respectively). Notably, nine strains of biocontrol bacteria were isolated. Three synthetic bacterial consortia were then constructed based on inhibitory assays and the dissolving rates of phosphorus and potassium exhibited by the candidate bacteria. The synthetic bacterial consortia were evaluated for biocontrol and growth promotion properties. The constructed synthetic consortium with the best performance reduced the average morbidity and mortality of treated plants by 27.59 % and 55.56 %, respectively, compared to the untreated control. In summary, synthetic bacterial consortium I (SCI) exhibited the best disease control and growth-promoting effects on tree peony. Using a synthetic bacterial consortium represents a new and novel approach to the biological control of peony root rot.