Aphid-induced tobacco resistance against Ralstonia solanacearum is associated with changes in the salicylic acid level and rhizospheric microbial community

In nature, plants are typically exposed to various pathogens. A pathogen infestation either strengthens or weakens plant resistance against subsequent pathogen attacks, depending on the different plant-pathogen systems. In this study, it is reported that aphids induce tobacco systemic acquired resistance against the soil-borne bacterium Ralstonia solanacearum. It was found that aphid feeding significantly reduced the disease index and wilt symptoms during R. solanacearum infection, and tobacco resistance positively correlated with aphid density within certain ranges. Analysis of the hormone levels demonstrated that salicylic acid content significantly increased in tobacco leaves and roots, whereas jasmonic acid levels remained unchanged. The expression of defense-related genes was upregulated in both the leaves and roots, and the activities of the defense-related enzymes increased. In addition, microbiological analyses of the rhizosphere revealed that the richness, community structure, and composition of the soil fungi and bacteria changed significantly during aphid infestation. These data indicate that aphid feeding not only induces systemic resistance to R. solanacearum infection but also affects the rhizospheric microbial community, which could result in feedback on plant growth and pathogen control.