Biochar contributes to resistance against root rot disease by stimulating soil polyphenol oxidase

Biochar has been considered an effective approach as soil amendment for decreasing incidences of disease and regulating microbial populations in continuous- cropping soil. Although researches have extensively focused on changes of soil microbes and unbalance of nutrition in continuous-cropping soil, the relationship between soil properties and pathogens by biochar application remains poorly understood. In this study, we applied ITS ribosomal RNA gene profiling to analyze tobacco root microbiota of biochar and non-biochar treatment in a 3-year continuous-cropping tobacco field, comparing firstly planting tobacco as control. We found that biochar application decreased the relative abundance of the soil fungal pathogens (Ceratobasidium and Monosporascus), which are the prime pathogens of tobacco root rot in continuous-cropping soil. Using RDA, co- occurrence and PLS-PM approaches, we provided evidence that there was a negative correlation between fungal genera (especially for Ceratobasidium and Monosporascus) and soil polyphenol oxidase (PPO) activity ( R-2 (incidence rate) = - 0.930, R-2 (disease index) = - 0.905, both p < 0.001). The PPO was up-regulated by different biochar treatment intensities. Together, we demonstrated that biochar in continuouscropping soil regulated the soil PPO activity to suppress pathogens, and further decrease incidence of root rot. Notably, biochar application forward continuous cropping was more effective for the continuous-cropping soil improvement than the other treatments. The data should help in appropriate timing of biochar application for alleviating continuous- cropping obstacle.

Automated summary

This study analyzed the tobacco root microbiota in a continuous-cropping tobacco field with and without biochar treatment. The results showed that biochar application reduced the abundance of soil fungal pathogens and decreased the incidence of root rot. The study also demonstrated that the regulation of soil polyphenol oxidase (PPO) activity by biochar played a key role in suppressing pathogens. The findings suggest that biochar application can be an effective strategy for improving continuous-cropping soil.