Compositional and functional comparison on the rhizosphere microbial community between healthy and Sclerotium rolfsii-infected monkshood (Aconitum carmichaelii) revealed the biocontrol potential of healthy monkshood rhizosphere microorganisms

Southern blight of monkshood (Aconitum carmichaelii Debx.) caused by Sclerotium rolfsii is one of the most destructive diseases causing tuber rot in the monoculture system. No studies have explored the differences of rhizosphere microbial communities between healthy and S. rolfsii-infected monkshood plants. Further, it remains unknown whether the rhizosphere microorganisms are associated with plant resistance to S. rolfsii infection. Therefore, in this study, the relationship between rhizosphere microorganisms and plant health of monkshood was assessed after S. rolfsii infection. High-throughput sequencing and culture-dependent methods were used to analyze the rhizosphere microbiome of healthy and diseased monkshood plants. Petri dish assays were performed to determine the effects of 10 dominant isolates from healthy or diseased samples on the growth of S. rolfsii hyphae and melon seedlings (as a model plant to test the plant growth promotion effect of these isolates). Two synthetic communities were constructed to verify the effects of dominant isolates on the growth and resistance of monkshood plants in pots after infection. The results showed that there were pronounced structural and functional differences in the bacterial and fungal communities between the rhizosphere soils of healthy and diseased plants. The diluted culture filtrates of some dominant isolates from diseased samples (such as Humicola fuscoatra and Fusarium commune) either promoted hyphal growth of S. rolfsii or inhibited seedling growth of melon; the synthetic community showed an inhibitory effect on monkshood growth and leaf L-phenylalanin ammonia-lyase activity, resulting in early and severe symptoms. Conversely, the diluted culture filtrates of some dominant isolates from healthy samples (such as Trichoderma hamatum and Streptomyces fungicidicus) inhibited S. rolfsii growth while promoting melon growth; the synthetic community elicited an improvement of monkshood growth and defense enzyme activity, resulting in mild symptoms. The results provide new insight into the role of rhizosphere microorganisms in plant health and open new avenues for controlling southern blight of monkshood.