Localized and systemic increase of phenols in tomato roots induced by Glomus versiforme inhibits Ralstonia solanacearum

Ralstonia solanacearum is an important plant pathogen in tropical and subtropical countries. Here, we describe the inhibition of R. solanacearum as a result of increased phenols induced locally or systemically by an arbuscular mycorrhizal (AM) fungus. In pot cultures, R. solanacearum populations in the rhizosphere, on root surfaces and in the xylem were decreased by 26.7, 79.3 and 81.7%, respectively, following inoculation of tomato plants (Lycopersicon esculentum Mill.) with Glomus versiforme Berch. Colonization of the plants by both R. solanacearum and G. versiforme increased the contents of soluble phenols and cell-wall bound phenols in root tissue, but with different patterns. Whereas R. solanacearum preferably promoted the cell-wall bound phenol content, G. versiforme preferably enhanced the soluble phenol content. Split root experiments revealed that R. Solanacearum was inhibited by G. versiforme, and that G. versiforme also increased the phenol content systemically, but to a lesser extent than locally.