Shared Core Microbiome and Functionality of Key Taxa Suppressive to Banana Fusarium Wilt

Microbial contributions to natural soil suppressiveness have been reported for a range of plant pathogens and cropping systems.To disentangle the mechanisms underlying suppression of banana Panama disease caused by Fusarium oxysporum f.sp.cubense tropical race 4(Foc4),we used amplicon sequencing to analyze the composition of the soil microbiome from six separate locations,each comprised of paired orchards,one potentially suppressive and one conducive to the disease.Functional potentials of the microbiomes from one site were further examined by shotgun metagenomic sequencing after soil suppressiveness was confrmed by greenhouse experiments.Potential key antagonists involved in disease suppression were also isolated,and their activities were validated by a combination of microcosm and pot experiments.We found that potentially suppressive soils shared a common core community with relatively low levels of F.oxysporum and relatively high proportions of Myxococcales,Pseudomonadales,and Xanthomonadales,with five genera,Anaeromyxobacter,Kofleria,Plesiocystis,Pseudomonas,and Rhodanobacter being significantly enriched.Further,Pseudomonas was identified as a potential key taxon linked to pathogen suppression.Metagenomic analysis showed that,compared to the conducive soil,the microbiome in the disease suppressive soil displayed a significantly greater incidence of genes related to quorum sensing,biofilm formation,and synthesis of antimicrobial compounds potentially active against Foc4.We also recovered a higher frequency of antagonistic Pseudomonas isolates from disease suppressive experimental field sites,and their protective effects against banana Fusarium wilt disease were demonstrated under greenhouse conditions.Despite differences in location and soil conditions,separately located suppressive soils shared common characteristics,including enrichment of Myxococcales,Pseudomonadales,and Xanthomonadales,and enrichment of specific Pseudomonas populations with antagonistic activity against the pathogen.Moreover,changes in functional capacity toward an increase in quorum sensing,biofilm formation,and antimicrobial compound synthesizing involve in disease suppression.

Root exudates mediate plant defense against foliar pathogens by recruiting beneficial microbes

Plants are capable of releasing specific root exudates to recruit beneficial rhizosphere microbes upon foliar pathogen invasion attack,including long-chain fatty acids,amino acids,short-chain organic acids and sugars.Although long-chain fatty acids and amino acids application have been linked to soil legacy effects that improve future plant performance in the presence of the pathogen,the precise mechanisms involved are to a large extent still unknown.Here,we conditioned soils with long-chain fatty acids and amino acids application(L+A)or short-chain organic acids and sugars(S+S)to examine the direct role of such exudates on soil microbiome structure and function.The L+A treatment recruited higher abundances of Proteobacteria which were further identified as members of the genera Sphingomonas,Pseudomonas,Roseiflexus,and Flavitalea.We then isolated the enriched bacterial strains from these groups,identifying ten Pseudomonas strains that were able to help host plant to resist foliar pathogen infection.Further investigation showed that the L+A treatment resulted in growth promotion of these Pseudomonas strains.Collectively,our data suggest that long-chain fatty acids and amino acids stimulated by foliar pathogen infection can recruit specific Pseudomonas populations that can help protect the host plant or future plant generations.