Page 2 Plant-Bacteria Interactions Edited by Iqbal Ahmad, John ...

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Pseudomonas aurantiaca SR1: Plant Growth Promoting Traits,
Secondary Metabolites and Crop Inoculation Response
Marisa Rovera, Evelin Carlier, Carolina Pasluosta, Germán Avanzini, Javier Andrés,
and Susana Rosas
8.1
Plant Growth Promoting Rhizobacteria: General Considerations
Natural agricultural ecosystems depend directly on microorganisms present in the
soil and soil rhizosphere that lead to increase in crop yield. Beneficial rhizosphere
microorganisms are important determinants of plant health and soil fertility
since they participate in many key ecosystem processes such as those involved in
the biological control of plant pathogens, nutrient cycling and seedling establishment
[1]. However, the natural role of rhizospheric microorganisms has been marginalized
because of conventional farming practices such as tillage and high inputs
of inorganic fertilizers and pesticides [2].
The recent progress in our understanding of the biological interactions occurring
in the rhizosphere and of the practical requirements for inoculant formulation and
delivery should increase the technology s reliability in the field and facilitate its
commercial development.
Plant growth promoting rhizobacteria (PGPR) were first defined by Kloepper and
Schroth [3] as soil bacteria that colonize the plant roots after they are inoculated onto
seeds and enhance plant growth [3]. The following actions are implicit in the
colonization process: ability to survive inoculation onto seed, to multiply in the
spermosphere (region surrounding the seed) in response to seed exudates, to attach
to the root surface and to colonize the developing root system [4].
PGPR enhance plant growth by direct and indirect means, but the specific mechanisms
involved have not yet been well explained [4,5]. Direct mechanisms of
plant growth promotion by PGPR can be demonstrated in the absence of plant
pathogens or other rhizospheric microorganisms, whereas indirect mechanisms
involve the ability of PGPR to reduce the deleterious effects of plant pathogens on
crop yield. PGPR have been reported to enhance plant growth directly by means of a
variety of mechanisms, including fixation of atmospheric nitrogen that is transferred
to the plant, production of siderophores that chelate iron and make it available
Plant-Bacteria Interactions. Strategies and Techniques to Promote Plant Growth
Edited by Iqbal Ahmad, John Pichtel, and Shamsul Hayat
Copyright Ó 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
ISBN: 978-3-527-31901-5
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