Mechanism of the antifungal action of chloropicrin fumigation against Panax notoginseng root rot caused by Fusarium solani

Fusarium root rot caused by Fusarium solani severely damages the roots of Panax notoginseng (ginseng) seedlings eventually leading in most cases to the total loss of this valuable crop. Soil fumigants are generally better at controlling soil-borne diseases such as F. solani than fungicides which provide unacceptable control. Therefore, this study aimed at evaluating the efficacy of fumigant chloropicrin (Pic) against F. solani in both laboratory and field. Ultrastructural changes in the mycelia of F. solani in each treatment were indicative of structural changes at the cellular level by transmission electron microscopy (TEM). Bacterial and fungal communities and diversity were targeted for Illumina high-throughput sequencing. Results indicated that chloropicrin inhibited F. solani mycelial growth completely at a concentration of 1.2 μg/l. In addition, ultrastructural studies showed that Pic caused plasmolysis and plasma leakage, indicating that the cell membrane of F. solani was disrupted. In the field trials, Pic at 45 g/m2 yielded an excellent long-term control of target pathogens, and treated plots allowed P. notoginseng plants to maintain vigorous growth compared with the untreated controls. Illumina MiSeq sequencing results revealed that bacterial communities were affected more seriously by Pic than fungi. The beneficial microbes (such as Trichoderma and Chaetomium) gradually increased, and the harmful microbes (such as Fusarium) decreased in fumigated soil. Together, the promotion of beneficial microorganisms and the direct inhibition of F. solani by chloropicrin were the main mechanisms for the prevention and control of soil-borne diseases. Our results provide useful information understanding chloropicrin fumigation against soil-borne disease.