Thymol and eugenol nanoparticles elicit expression of Ralstonia solanacearum virulence and potato defense genes and are potential bactericides against potato bacterial wilt

Bacterial wilt disease caused by Ralstonia solanacearum impacts negatively on potato production. This study evaluated the effects of thymol and eugenol encapsulated in chitosan nanoparticles (TCNP and ECNP) on the virulence genes (PhcA, XpsR and HrpG) of R. solanacearum and their in vivo efficacy against bacterial wilt. Gene expression levels of virulence genes in the presence of TCNP (5.6 and 11.3 µg mL−1) and ECNP (11.3 and 22.5 µg mL−1) together with those of plant defense genes (chitinase and β-l,3-glucanase) were determined through RT-qPCR. All the virulence genes were downregulated when exposed to both TCNP and ECNP while glucanase and chitinase genes increased and peaked after 18 hours post inoculation. The lowest disease severity index (10.3%) was recorded with plants treated with 90 µg mL−1 ECNP. The results of this study show that both TCNP and ECNP have a potential to be used as bacterial wilt bactericides.