Stimulation of Plant Growth and Drought Tolerance by Native Microorganisms (AM Fungi and Bacteria) from Dry Environments: Mechanisms Related to Bacterial Effectiveness |
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Authors: | Adriana Marulanda José-Miguel Barea Rosario Azcón |
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Institution: | (1) Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín (CSIC), Profesor Albareda no 1, E-18008 Granada, Spain |
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Abstract: | In this study we tested whether rhizosphere microorganisms can increase drought tolerance to plants growing under water-limitation
conditions. Three indigenous bacterial strains isolated from droughted soil and identified as Pseudomonas putida, Pseudomonas sp., and Bacillus megaterium were able to stimulate plant growth under dry conditions. When the bacteria were grown in axenic culture at increasing osmotic
stress caused by polyethylene glycol (PEG) levels (from 0 to 60%) they showed osmotic tolerance and only Pseudomonas sp. decreased indol acetic acid (IAA) production concomitantly with an increase of osmotic stress (PEG) in the medium. P. putida and B. megaterium exhibited the highest osmotic tolerance and both strains also showed increased proline content, involved in osmotic cellular
adaptation, as much as increased osmotic stress caused by NaCl supply. These bacteria seem to have developed mechanisms to
cope with drought stress. The increase in IAA production by P. putida and B. megaterium at a PEG concentration of 60% is an indication of bacterial resistance to drought. Their inoculation increased shoot and
root biomass and water content under drought conditions. Bacterial IAA production under stressed conditions may explain their
effectiveness in promoting plant growth and shoot water content increasing plant drought tolerance. B. megaterium was the most efficient bacteria under drought (in successive harvests) either applied alone or associated with the autochthonous
arbuscular mycorrhizal fungi Glomus coronatum, Glomus constrictum or Glomus claroideum.
B. megaterium colonized the rhizosphere and endorhizosphere zone. We can say, therefore, that microbial activities of adapted strains represent
a positive effect on plant development under drought conditions. |
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Keywords: | Bacteria Arbuscular mycorrhizal fungi Drought tolerance |
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