Induction of systemic resistance in potato by rhizobacterium Rhizobium etli strain G12 is not associated with accumulation of pathogenesis-related proteins and enhanced lignin biosynthesis

Whereas pathogen- and chemically induced systemic resistance in plants is characterized by enhanced accumulation of pathogenesis-related (PR) proteins; increased peroxidase activity and cell wall modifications such as lignification, the signal transduction pathways fdr; rhizobacteria-induced systemic resistance are poorly understood. The rhizobacterium Rhizobium etli strain G12 has been shown to induce systemic resistance in potato towards the potato cyst nematode Globodera pallida. The results presented here clearly demonstrated that the resistance reaction triggered by Rhizobium etli G12 was not accompanied by enhanced accumulation of PR proteins such as chitinase and beta -1,3-glucanase. This was demonstrated in the presence as well as in the absence of the nematode. Peroxidase activity was only enhanced after challenge inoculation with the nematode. The highest levels, of peroxidase activity were achieved in non-bacterized roots, indicating a general stress response of the plant to nematode attack. In contrast to other plant defense reactions where enhanced peroxidase activity is associated with an increased lignification of root cells as mechanical barrier against pathogen attack, lignin content was not affected in bacteria-treated roots. It is concluded that rhizobacteria-induced systemic resistance triggers a signal transduction pathway different from common pathogen or chemical induced pathways.