Root exudates of potato onion are involved in the suppression of clubroot in a Chinese cabbage-potato onion-Chinese cabbage crop rotation

Clubroot, caused by Plasmodiophora brassicae, has emerged as a serious disease threatening cruciferous crop production throughout the world. Crop rotation with non-host species is commonly practised to avoid clubroot, but it is not known whether rotation crops can control clubroot when the resting spores of P. brassicae remain unaffected. Pot experiments were performed to investigate the response of clubroot in Chinese cabbage to crop rotation with potato onion. The results showed that Chinese cabbage rotated with potato onion exhibited less clubroot disease than Chinese cabbage monoculture. Compared with residues from potato onion, the addition of root exudates from potato onion significantly decreased the disease incidence and index of clubroot (p ≤ 0.05). Potato onion root exudates decreased the number of secondary plasmodia of P. brassicae and the expression of the PRO1 gene of P. brassicae. These results suggest that root exudates from potato onion may play an important role in suppressing clubroot in a Chinese cabbage-potato onion-Chinese cabbage rotation system.