Crop Rotation with Marigold Promotes Soil Bacterial Structure to Assist in Mitigating Clubroot Incidence in Chinese Cabbage

Clubroot caused by Plasmodiophora brassicae is an economically important soilborne disease of Chinese cabbage worldwide. Integrated biological control through crop rotation is considered a good disease management approach to suppress the incidence of soilborne diseases. In this study, we evaluated the effect of a marigold plant (root exudates, crude extract, and powder) on the germination and death of resting spores of P. brassicae in vitro assays. Additionally, we also performed 16S high throughput sequencing, to investigate the impact of marigold–Chinese cabbage crop rotation on soil bacterial community composition, to manage this devastating pathogen. This study revealed that the marigold root exudates, crude extract, and powder significantly promoted the germination and death of P. brassicae resting spores. Under field conditions, marigold–Chinese cabbage crop rotation with an empty period of at least 15 days enhanced the germination of P. brassicae resting spores, shifted the rhizosphere bacterial community composition, and suppressed the incidence of clubroot by up to 63.35%. Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria, and Verrucomicrobia were the most dominant phyla and were present at high relative levels in the rhizosphere soil of Chinese cabbage. We concluded that crop rotation of Chinese cabbage with marigold can significantly reduce the incidence of clubroot disease in the next crop. To our knowledge, this is the first comprehensive study on the prevention and control of clubroot disease in Chinese cabbage through crop rotation with marigold.