Application of vermicompost and biochar suppresses Fusarium root rot of replanted American ginseng.

Soil sterilization integrated with agronomic measures is an effective method to reduce soilborne replant diseases. However, the effect of vermicompost or biochar application after soil sterilization on soilborne diseases is poorly understood. A pot experiment was conducted in American ginseng to investigate the effects of vermicompost (VF), biochar (BF), and a combination of vermicompost and biochar (VBF) applied after soil sterilization on the incidence of Fusarium root rot using natural recovery (F) as control. After one growing season, the disease index of root rot, the phenolic acids, and the microbial communities of American ginseng rhizosphere soil were analyzed. The disease index of VF, BF, and VBF decreased by 33.32%, 19.03%, and 80.96%, respectively, compared with F. The highest bacterial richness and diversity were observed in the rhizosphere soil of VBF. Besides, VF and VBF significantly increased the relative abundance of beneficial bacteria (Pseudomonas, Lysobacter, and Chryseolinea) in the rhizosphere soil. Higher concentrations of vanillin, one of the phenolic acids in the roots exudates, were recorded in the rhizosphere soils of BF and VBF. The vanillin concentration showed a significant negative correlation with the disease index. To conclude, vermicompost improved the beneficial bacteria of the rhizosphere soil, while biochar regulated the allelopathic effect of the phenolic acids. The study proposes a combined application of biochar and vermicompost to the rhizosphere soil to control Fusarium root rot of replanted American ginseng effectively. KEY POINTS: Vermicompost improves the relative abundance of rhizosphere beneficial bacteria. Biochar inhibits the degradation of phenolic acids by adsorption. The combination of vermicompost and biochar enhances the disease control effect.

The relationship between shifts in the rhizosphere microbial community and root rot disease in a continuous cropping American ginseng system.

The root rot disease causes a great economic loss, and the disease severity usually increases as ginseng ages. However, it is still unclear whether the disease severity is related to changes in microorganisms during the entire growing stage of American ginseng. The present study examined the microbial community in the rhizosphere and the chemical properties of the soil in 1-4-year-old ginseng plants grown in different seasons at two different sites. Additionally, the study investigated ginseng plants' root rot disease index (DI). The results showed that the DI of ginseng increased 2.2 times in one sampling site and 4.7 times in another during the 4 years. With respect to the microbial community, the bacterial diversity increased with the seasons in the first, third, and fourth years but remained steady in the second year. The seasonal changing of relative abundances of bacteria and fungi showed the same trend in the first, third, and fourth years but not in the second year. Linear models revealed that the relative abundances of Blastococcus, Symbiobacterium, Goffeauzyma, Entoloma, Staphylotrichum, Gymnomyces, Hirsutella, Penicillium and Suillus spp. were negatively correlated with DI, while the relative abundance of Pandoraea, Rhizomicrobium, Hebeloma, Elaphomyces, Pseudeurotium, Fusarium, Geomyces, Polyscytalum, Remersonia, Rhizopus, Acremonium, Paraphaeosphaeria, Mortierella, and Metarhizium spp. were positively correlated with DI (P < 0.05). The Mantel test showed that soil chemical properties, including available nitrogen, phosphorus, potassium, calcium, magnesium, organic matter, and pH, were significantly correlated to microbial composition. The contents of available potassium and nitrogen were positively correlated with DI, while pH and organic matter were negatively correlated with DI. In summary, we can deduce that the second year is the key period for the shift of the American ginseng rhizosphere microbial community. Disease aggravation after the third year is related to the deterioration of the rhizosphere microecosystem.