Elicitation of systemic resistance and growth promotion of Arabidopsis thaliana by PGPRs from Nicotiana glauca:: a study of the putative induction pathway

The ability of six putative plant growth promoting rhizobacteria, isolated from the rhizosphere of Nicotiana glauca L., to stimulate growth and induce systemic resistance against Xanthomonas campestris CECT 95 in Arabidopsis thaliana L. Col-0 was evaluated. The six bacterial strains significantly reduced the disease symptoms caused by the pathogen compared to the controls, with the best results obtained with the Bacillus strain N11.37 and the Stenotrophomonas strain N6.8. These two strains were tested on A. thaliana NahG plants and jar1-1 and etr1-1 mutants, to elucidate whether the salicylic acid (SA)-dependent or SA-independent pathway was involved in the induction of systemic resistance. The results indicate that N6.8 induces the SA-dependent pathway. For N11.37 it is as yet not clear as in the etr1-1 mutants and NahG plants ISR is not expressed, while in jar1-1 it is. In addition, levels of SA were measured in Col-0 plants treated with N6.8 and N11.37 to confirm whether or not the two strains produced an increased level of SA. N6.8- and N11.37-induced plants showed higher levels of SA than the controls. It is concluded that N6.8 induces a SA-dependent pathway while N11.37 induces a pathway that is both ethylene (ET)- and SA-dependent.