Pseudostellaria heterophylla cultivar mixtures driven changes in rhizosphere metabolites to suppress soil-borne Fusarium disease

Crop diversification contributes to a decrease in soil-borne crop diseases, as well as an increase in agricultural productivity. However, few studies have investigated the changes in the composition of the rhizosphere microbial communities and rhizosphere metabolites, as well as their suppressive effect on soil-borne diseases under different crop cultivar mixture regimes. We carried out a series of experiments to assess changes in the rhizosphere microbial community and metabolites profile under different Pseudostellaria heterophylla cultivar mixture cultivation in consecutive monoculture fields by employing amplicon metagenomics (16S rRNA, ITS, and 18S rRNA) and non-targeted metabolomics. The impact of key metabolites on pathogenic Fusarium oxysporum, crop growth, and soil microorganisms was assessed under controlled conditions. Our study indicated that the cultivar mixtures improved the P. heterophylla performance, increased the fresh root biomass by 81.9–115.4 % and the heterophyllin B content by 35 % compared to the consecutive monoculture, respectively. Cultivar mixtures increased the abundance of beneficial bacteria (Lactobacillus, Pseudomonas, Nitrosospira) and consumer protists, and decreased the abundance of pathogenic fungal genera (Fusarium, Alternaria, Curvularia, Stemphylium, Gibberella). The qPCR results indicated that the cultivar mixtures significantly decreased the abundance of pathogenic F. oxysporum by 64.0–84.3 % compared to the consecutive monoculture treatment. Non-targeted metabolomics analysis showed that the cultivar mixtures significantly altered the soil metabolite profiles, and increased the contents of d-galactose, galactinol, d-sorbitol, glycerol, melibiose, D-fructose and D-tagatose. Subsequently, the key upregulated metabolites (glycerol, d-fructose, gluconic acid, quinic acid, and l-valine), identified through the random forest analysis, significantly inhibited the growth of F. oxysporum. The crucial metabolites in the presence of a pathogen (F. oxysporum) and single metabolite treatment significantly increased the biomass, SOD and CAT activity and decreased the POD and MAD activity of P. heterophylla compared to FOP (F. oxysporum treatment). Furthermore, the crucial metabolites under pathogen treatment significantly lowered the abundance of total fungi and F. oxysporum and increased the abundance of Pseudomonas spp. compared to FOP. Therefore, our study was able to emphasize the efficacy of using cultivar mixtures to combat soil-borne Fusarium disease through the modulation of rhizosphere metabolites.