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

Abstract

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 (R2incidence rate = − 0.930, R2disease index = − 0.905, both p < 0.001). The PPO was up-regulated by different biochar treatment intensities. Together, we demonstrated that biochar in continuous-cropping 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. Graphical abstract

Relief effect of biochar on continuous cropping of tobacco through the reduction of p-hydroxybenzoic acid in soil

“…Therefore, studies on the interactions among biochar, autotoxins and rhizosphere microorganisms could lay a theoretical foundation for alleviating obstacles to continuous cropping. In our previous experiments, we demonstrated that biochar regulates soil PPO activity in continuously cropped soil to suppress pathogens and decrease the incidence of root rot [ 12 ]. This conclusion aligns well with reports from previous literature [ 17 ].…”

“…The tobacco straw used in this study was obtained from the Rice Research Institute of Shenyang Agricultural University, China. According to previous studies conducted in our laboratory, biochar produced at 450 °C from a laboratory muffle furnace is suitable for improving continuously cropped soil [ 12 ]. In these studies, biochar was produced in a factory; hence, we recommend that biochar be produced at 400 °C, which corresponds to an actual temperature of ∼450 °C according to the instructions of the carbonisation furnace manufacturer.…”

“…However, when continuous cropping is practiced, allelochemicals build up in the soil. When the allelochemical content of soils exceeds a certain threshold, the germination, growth, survival and reproduction of neighbouring plants and microorganisms are suppressed [ 12 ]. These allelochemicals that have negative effects are referred to as auto-toxic compounds [ 11 ].…”

“…However, the underlying mechanism for inhibiting the incidence rate of disease and promoting plant growth remains unknown. Our previous study indicated that in continuously cropped soil, biochar regulates soil PPO activity to suppress pathogens and decrease the incidence of root rot [ 12 ]. For auto-toxic compounds, continuous-cropping obstacles in soil originate from the long-term accumulation of autotoxins, including ginsenosides and phenolic acids [ 20 ].…”