Responses of the potato rhizosphere bacterial communities to Ralstonia solanacearum infection and their roles in binary disease outcomes

Aims

Bacterial wilt, caused by Ralstonia solanacearum (Rs), often presents as a symptomless latent infection where plants test positive for Rs but exhibit no visible symptoms. While latent infection is associated with pathogen exposure, the role of rhizosphere microorganisms in plant resistance remains unclear. This study aimed to investigate whether latently infected potato plants can recruit beneficial microbiomes to mitigate Rs infection.

Methods

Two potato cultivars, H15 (high susceptibility) and Q9 (low susceptibility), were tested under high pathogen pressure. Full-length 16S rRNA sequencing and microbial network analyses were conducted on rhizosphere samples to assays microbiome responses. Plate inhibition assays and greenhouse inoculation trials were used to screen and validate potential beneficial bacteria from latently infected samples.

Results

Resistance to infection differed significantly between the two cultivars, with 86.67% of H15 and 38.71% of Q9 plants developing symptoms, while latent infections were more frequent in Q9 (61.29%) than in H15 (13.33%). α- and β-diversity analyses revealed distinct microbial communities between diseased and latently infected plants. The Shannon index was positively correlated with disease severity (Spearman’s r = 0.733, p = 0.016), and β-diversity analysis revealed a significant association between microbial community composition and disease progression (Mantel r = 0.859, p = 0.0015). Robust microbial networks with higher modularity and clustering coefficients were observed in latently infected Q9 plants, enriched with Pseudomonas and Bacillus. We isolated 43 bacterial strains and clustered them into seven OTUs. Pseudomonas putida XC1 showed the strongest inhibition against Rs and effectively reduced wilt symptoms in greenhouse assays.

Conclusions

Latently infected plants actively recruit and assemble beneficial rhizosphere microbiomes, which enhance microbial network stability and suppress pathogen activity. This microbiome-mediated resistance highlights the potential of using beneficial microbes for sustainable disease control.