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 of Trichodermaharzianum LTR-2 inoculation on the rhizosphere community of Chinese cabbage (Brassica rapa subsp. pekinensis cv. Jiaozhou) in a commercial production area. T. harzianum inoculation 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 of Plasmodiaphora brassicae, the causative pathogen of cabbage clubroot disease, and its copy number in rhizosphere soil. Pathogenic fungi Alternaria and Fusarium were also negatively associated with Trichoderma inoculation according to co-occurrence network analysis. Inoculation drastically reduced the relative abundance of the dominant bacterial genera Delftia and Pseudomonas, whilst increasing others including Bacillus. Our results demonstrate that T. harzianum LTR-2 is an effective biological control agent for cabbage clubroot, which acts through modulation of the soil and rhizosphere microbial community.

Fusarium crown rot and wheat sharp eyespot are major soil-borne diseases of wheat, causing serious losses to wheat yield in China. We applied high-throughput sequencing combined with qPCR to determine the effect of winter wheat seed dressing, with either Trichoderma atroviride HB20111 spore suspension or a chemical fungicide consisting of 6% tebuconazole, on the fungal community composition and absolute content of pathogens Fusarium pseudograminearum and Rhizoctonia cerealis in the rhizosphere at 180 days after planting. The results showed that the Trichoderma and chemical fungicide significantly reduced the amount of F. pseudograminearum in the rhizosphere soil (p < 0.05), and also changed the composition and structure of the fungal community. In addition, field disease investigation and yield measurement showed that T. atroviride HB20111 treatment reduced the whiteheads with an average control effect of 60.1%, 14.9% higher than the chemical treatment; T. atroviride HB20111 increased yield by 7.7%, which was slightly more than the chemical treatment. Therefore, T. atroviride HB20111 was found to have the potential to replace chemical fungicides to control an extended range of soil-borne diseases of wheat and to improve wheat yield.