Co-application of dazomet and azoxystrobin reconstructs soil microbial communities and suppresses the violet root rot...

Violet root rot (VRR) is a devastating soil-borne disease that severely affects Codonopsis tangshen (C. tangshen) production, with limited effective control strategies available. This study aimed to develop an effective method for controlling VRR and explore its underlying mechanisms. A 2-year field experiment was conducted to investigate the impact of dazomet fumigant alone (D) and in combination with azoxystrobin (DA) on the yield, VRR incidence, medicinal component level, soil biochemical properties, and rhizosphere microbial community structure of continuously cropped C. tangshen. The results showed that both D and DA significantly increased the yield by 112.3% and 173.8% in 2019, and by 179.1% and 520.9% in 2020, respectively. Moreover, D and DA significantly reduced the VRR incidence by 87.9% and 100.0% in 2019, and by 14.7% and 100.0% in 2020, respectively. Furthermore, treatments D and DA changed the levels of certain medicinal components, altered partial soil biochemical properties (including pH, enzyme activities, and nutrient levels), and shifted the soil microbial community structure. Notably, the DA treatment significantly decreased the abundance of potential soil-borne pathogen Helicobasidium, while increasing the abundance of potential pathogen-suppressive microbes like Rhodanobacter, Saccharimonadales, Acidothermus, and Tetracladium, in both 2019 and 2020. The reduced pathogen abundance and restructured microbial community may collectively contribute to the complete suppression of VRR under DA treatment. This study offers an effective strategy for controlling VRR in C. tangshen under continuous cropping systems, contributing to the sustainable development of the C. tangshen industry.IMPORTANCEAs a valuable medicinal and edible plant, Codonopsis tangshen significantly contributes to rural economies in China's mountainous areas. However, its cultivation faces severe threats from violet root rot (VRR), a devastating soil-borne disease lacking effective control measures. Our study demonstrated that combined soil fumigation and azoxystrobin application (DA) completely prevented VRR occurrence for 2 years while simultaneously reducing pathogen abundance and restructuring the soil microbial community, which may be key factors in disease suppression. This study provides novel insights into the mechanisms underlying the complete control of VRR by DA treatment and is beneficial for the high-quality development of the C. tangshen industry.