Effects of Soil Disinfection Using Chlorine Dioxide on Soil Fungal Communities in Apple Replant Fields and the Growth of Malus hupehensis Rehd. Seedlings

The effectiveness of chlorine dioxide as a soil disinfectant for the prevention and control of apple replant disease (ARD) remains largely unexplored. This study aimed to determine the optimal concentration of chlorine dioxide for soil disinfection and to evaluate its impact on the prevention and control of ARD. The experimental results indicated that a high concentration of 600 mg·L−1 chlorine dioxide exhibited a potent lethal effect on both the hyphae and spores of pathogenic Fusarium. Results from pot experiments demonstrated that, compared with the replant control, the height, ground diameter, fresh weight, and dry weight of Malus hupehensis Rehd. seedlings treated with 600 mg·L−1 chlorine dioxide increased by 27.20%, 15.95%, 100.70%, and 76.28%, respectively. Additionally, the root length, surface area, volume, and number of root tips of the seedlings increased by 31.74%, 96.54%, 257.29%, and 85.29%, respectively. The activities of root-protective enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), also increased to varying degrees, whereas the malondialdehyde (MDA) content was significantly reduced compared with the control treatment. Furthermore, the number of soil fungi treated with chlorine dioxide and the concentration of phenolic acid compounds in replant soil were significantly reduced. Treatment with 600 mg·L−1 chlorine dioxide significantly decreased the detected copy number of genes associated with soil-borne pathogenic Fusarium, optimized the soil microbial community structure, and reduced the relative abundance of pathogenic fungi. In summary, disinfection of replant soil using 600 mg·L−1 chlorine dioxide can enhance the growth of M. hupehensis Rehd. seedlings, inhibit the growth and reproduction of pathogenic Fusarium fungi, improve the soil environment, and effectively prevent and control ARD.