Lipopolysaccharides of Rhizobium etli strain G12 act in potato roots as aninducing agent of systemic resistance to infection by the cyst nematode Globodera pallida

Recent studies have shown that living and heat-killed cells of the rhizobac terium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematode Globodera pallida, To better unde rstand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat-stable bacterial surface carbohydrates such as e xopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for rec ognition in the symbiotic interaction between Rhizobium and legumes, their role in the R, etli-potato interaction was studied. EPS and LPS were extrac ted from bacterial cultures, applied to potato roots, and tested for activi ty as an inducer of plant resistance to the plant-parasitic nematode, Where as EPS did not affect G, pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml(-1), Split-root e xperiments, guaranteeing a spatial separation of inducing agent and challen ging pathogen, showed that soil treatments of one half of the root system w ith LPS resulted in a highly significant (up to 37%) systemic induced reduc tion of G, pallida infection of potato roots in the other half. The results clearly showed that LPS of R, etli G12 act as the inducing agent of system ic resistance in potato roots.