Abstract:

In this potted experiment, organic milk cabbage （Brassica campestris ssp. chinensis L.） was used as the test crop. Seven treatments were established, including five rotation treatments without conventional disease management: garlic−milk cabbage（A）, lettuce−milk cabbage（B）, capsicum−milk cabbage（C）, green bean−milk cabbage（D） and coriander−milk cabbage（E）, and two control treatments: continuous cropping of milk cabbage without （F） and with （G） conventional disease management. The effects of different rotation patterns on the yield and quality of organic milk cabbage, the structure of soil microbial community and the control of clubroot disease were investigated. This study sought to unravel the mechanisms underlying the control of clubroot disease by various preceding crops. The results showed that the garlic−milk cabbage rotation（A） and coriander−milk cabbage rotation（E） exhibited the most comprehensive performance in suppressing clubroot disease, markedly reducing disease incidence, with the garlic−milk cabbage rotation（A） resulting in the lowest disease index at only 2.31%. Both rotation treatments significantly increased the α−diversity of rhizosphere microorganisms（as indicated by Chao1 and Shannon indices） and improved soil physicochemical properties. The disease suppression mechanisms differed between the two rotations. When coriander was used as the preceding crop, it enhanced the activity of antioxidant enzymes（e.g., peroxidase, POD）, strengthening the defensive responses of milk cabbage. In contrast, when garlic was the preceding crop, it promoted the synergistic interaction of hormones, such as abscisic acid（ABA） and gibberellic acid（GA₃）, which in turn improved overall plant growth regulation and resistance. However, capsicum−milk cabbage rotation（C） and continuous cropping of milk cabbage without conventional disease management（F） led to reduced microbial diversity and increased disease pressure. Continuous cropping of milk cabbage with conventional disease management（G） did alleviate clubroot disease to a certain extent, but its control efficacy remained significantly inferior to that of the rotation treatments.

Key words: Cruciferous vegetables, Soil?borne diseases, Farming system, Disease index, Yield, Soil microorganism