Trichoderma harzianumInoculation Reduces the Incidence of Clubroot Disease in Chinese Cabbage by Regulating the Rhizosphere Microbial Community

Clubroot is a disease of cruciferous crops that causes significant economic losses to vegetable production worldwide. We applied high-throughput amplicon sequencing technology to quantify the effect ofTrichodermaharzianumLTR-2 inoculation on the rhizosphere community of Chinese cabbage (Brassica rapasubsp.pekinensiscv. Jiaozhou) in a commercial production area.T. harzianuminoculation of cabbage reduced the incidence of clubroot disease by 45.4% (p< 0.05). The disease control efficacy (PDIDS) was 63%. This reduction in disease incidence and severity coincided with a drastic reduction in both the relative abundance ofPlasmodiaphora brassicae, the causative pathogen of cabbage clubroot disease, and its copy number in rhizosphere soil. Pathogenic fungiAlternariaandFusariumwere also negatively associated withTrichodermainoculation according to co-occurrence network analysis. Inoculation drastically reduced the relative abundance of the dominant bacterial generaDelftiaandPseudomonas, whilst increasing others includingBacillus. Our results demonstrate thatT. harzianumLTR-2 is an effective biological control agent for cabbage clubroot, which acts through modulation of the soil and rhizosphere microbial community.