Mesorhizobium huakuii 7653 R regulates the endophytic bacterial communities and disease resistance pathways to promote clubroot resistance in Brassica napus

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Clubroot is a global soilborne disease caused by Plasmodiophora brassicae that severely affects cruciferous crops. Currently, there are no effective control measures to completely eliminate pathogens in the field. Pot experiments have shown that treatment with Mesorhizobium huakuii 7653 R can relieve clubroot symptoms. However, whether M. huakuii 7653 R can be used in the field to control clubroot disease is unclear, and the mechanism of its resistance remains largely unknown. We conducted two seasons of field trials with Brassica napus and found that M. huakuii 7653 R treatment significantly reduced clubroot disease severity, and that the agronomic traits at the seedling, flowering, and harvesting stages were significantly improved compared to the control group. The average yield per hectare, thousand grain weight, and oil content increased by 83.1%, 10.4%, and 3.7%, respectively. M. huakuii 7653 R also enhanced the resistance and yield of the cruciferous plant Brassica campestris var. purpuraria to clubroot. We characterized the composition and structure of the endophytic microbiota using bacterial 16S sequencing, and showed that treatment with M. huakuii 7653 R shaped the structure of endophytic bacterial communities. The relative abundances of Actinobacteria and Bacteroidetes, which are resistant to oxidative stress, were enriched in the co-inoculation with M. huakuii 7653 R and P. brassicae on B. napus. Transcriptome data indicated that genes related to plant immunity, nitrogen uptake and metabolism were significantly up-regulated by co-inoculation with M. huakuii 7653 R and P. brassicae. Our findings provide a theoretical basis for the widespread application of M. huakuii 7653 R in clubroot biocontrol.

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