The ability of four plant growth-promoting rhizobacteria, isolated in a previous study, to induce systemic resistance on Arabidopsis thaliana Col 0 against biotic and abiotic stress was evaluated. All the bacteria enhanced protection against the foliar pathogen Pseudomonas syringae DC3000 and increased plant tolerance to salt stress (NaCl 60 mM). Bacillus sp. strain L81 and Arthrobacter oxidans strain BB1 performed best with a decrease in the disease index of 61.2 and 52.3%, respectively, and a reduction in the mortality due to salt stress of 72.4 and 57.8%, respectively. Additionally, significant differences were found in growth and photosynthesis, again, L81 and BB1 performed best either in normal or under stress conditions. In order to elucidate the pathway elicited by these two strains to induce systemic resistance, experiments with the transgenic line of Arabidopsis thaliana NahG (defective in salicylic acid [SA]) and with the jar1 mutant (defective in jasmonic acid) were carried out. Results showed that the SA-dependent pathway was involved in the defense response induced by strains L81 and BB1. Results from quantitative reverse transcription-polymerase chain reaction analysis of the PR1 gene, related to the SA-dependent pathway and the PDF1.2 gene related to the SA-independent pathway, showed an increased expression of PR1 in BB1-treated plants, confirming involvement of the SA-dependent pathway in the defensive response.
The effect of co-inoculation with Pisolithus tinctorius and a PGPR belonging to the genus Bacillus (Bacillus licheniformis CECT 5106 and Bacillus pumilus CECT 5105) in enhancing growth of Pinus pinea plants and the changes that occurred in rhizosphere microbial communities and the degree of mycorrhization were evaluated. Both bacterial strains of Bacillus promote the growth of Pinus pinea seedlings, but this biological effect does not imply a synergic effect with mycorrhizal infection. However, the positive response to mycorrhiza in a longer-term experiment it could be expected. The introduction of both inocula causes an alteration in the microbial rhizosphere composition, despite the low levels of inocula that were found at the end of the assay.
Summary
Two Gram‐negative, plant growth‐promoting rhizobacteria (PGPRs), denominated as M12 and M14, were classified by 16S rDNA sequencing as Burkholderia graminis species. Both strains were shown to produce a variety of N‐acyl‐homoserine lactone (AHL) quorum sensing (QS) signalling molecules. The involvement of these molecules in plant growth promotion and the induction of protection against salt stress was examined. AHL production was evaluated in vitro by thin‐layer chromatography using AHL biosensors, and the identity of the AHLs produced was determined by liquid chromatography‐tandem mass spectrometry. The in situ production of AHLs by M12 and M14 in the rhizosphere of Arabidopsis thaliana plants was detected by co‐inoculation with green fluorescent protein‐based biosensor strains and confocal laser scanning microscopy. To determine whether plant growth promotion and protection against salt stress were mediated by QS, these PGPRs were assayed on wild‐type tomato plants, as well as their corresponding transgenics expressing YenI (short‐chain AHL producers) and LasI (long‐chain AHL producers). In wild‐type tomato plants, only M12 promoted plant growth, and this effect disappeared in both transgenic lines. In contrast, M14 did not promote growth in wild‐type tomatoes, but did so in the LasI transgenic line. Resistance to salt stress was induced by M14 in wild‐type tomato, but this effect disappeared in both transgenic lines. The strain M12, however, did not induce salt resistance in wild‐type tomato, but did so in LasI tomato plants. These results reveal that AHL QS signalling molecules mediate the ability of both PGPR strains M12 and M14 to promote plant growth and to induce protection against salt stress.
The effects of inoculation with a strain of Bacillus licheniformis on the growth of pepper and tomato were investigated in three experiments, one under seedbed conditions and two under greenhouse production conditions. In the first experiment, the bacterium significantly increased the height of plants and the leaf area in both species and in both cultivars. Effects were greater on pepper than on tomato. In the second experiment, seedlings growing in sand and in hydroponic culture were studied. The number and diameter of tomato fruits produced in sand and in hydroponic medium were increased significantly by inoculation. Treated plants had less disease than non-treated plants. In the third experiment the total weight of pepper harvested from inoculated plants increased significantly with regard to control non-inoculated plants. This strain had considerable colonisation and competitive ability, and it could be used as a biofertiliser or biocontrol agent without altering normal management in greenhouses.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.