Phytostimulatory effect of Rhizobium and Plant Growth Promoting Rhizobacteria in common bean (Phaseolus vulgaris L.) interaction
Fecha
2008-12-20
Autores
Torres Gutiérrez, Roldán
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Editor
Universidad Central “Marta Abreu” de Las Villas. Facultad de Ciencias Agropecuarias. Departamento de Agronomía
Resumen
The symbiosis between plants of the Leguminosae family and prokaryotic partners is typically
characterized by the formation of specialized organs, called nodules, on plant roots or stems
that are invaded by the specific microsymbionts. These include the well-known alpha-
proteobacterial group of Rhizobiaceae containing the genera Rhizobium, Bradyrhizobium,
Sinorhizobium (Ensifer), Mesorhizobium, Azorhizobium, and Allorhizobium, collectively
referred as rhizobia. Legumes play a crucial role in sustainable agriculture. Symbiotic
nitrogen fixation (SNF) through interaction between legumes and rhizobia, contributes to
nitrogen (N) nutrition of most legumes and legume cropping systems. Common bean
(Phaseolus vulgaris L.) is the most important legume for direct human consumption
worldwide and particularly in many parts of Latin America and Africa. However, the
application of SNF in common bean in the field is often low compared to the nitrogen fixing
capacity of beans under optimal conditions and as compared to the amounts of nitrogen fixed
by other legumes.
The aim of our study is to identify, quantify and enhance the phytostimulatory effect of the
interplay between Rhizobium, bean genotypes and plant growth promoting rhizobacteria
(PGPR) under different growth conditions and to contribute to the understanding of the
molecular mechanisms involved in the Rhizobium-bean interaction.
To reach this objective, combinations of Rhizobium-PGPR were evaluated under different
growth conditions in Cuba using two local bean genotypes. The nodulation and plant growth
parameters were significantly stimulated with the combination of Rhizobium-Azospirillum
and Rhizobium-Azotobacter under pot experiment condition, as well as in a field trial.
Variations among genotypes were observed for growth parameters and yield in a second field
trial. The combination Rhizobium-Azospirillum and the fertilizer treatments showed the best
result in yield for ICA Pijao beans, while for BAT-304 beans the best result was obtained
with the single Rhizobium inoculation. Secondly, the morphological and genetic
characterization of bacterial isolates from Cuban bean fields, as well as the phenotypic
characterization of Cuban Rhizobium isolates under controlled and field conditions,
demonstrate the biodiversity of beneficial microbes in the common bean rhizosphere and the
stimulatory effect of compatible interactions between common bean genotypes and Rhizobium strains. The genetic characterization of isolated bacterial strains form Cuban soils
using 16S rDNA sequencing revealed 8 groups of bacteria belonging to the genera:
Agrobacterium, Rhizobium, Ochrobactrum, Sphingomonas, Stenotrophomonas, Bacillus,
Brevibacillus and Paenibacillus. In nodule samples, 37.5% of isolates were 100% similar to
Agrobacterium tumefaciens or Rhizobium species. This study allowed the identification of
two species of Rhizobium isolates (Rhizhobium etli and Rhizobium tropici) in nodule samples.
In nodulation tests Agrobacterium isolates were unable to nodulate the original host. The
phenotypic characterization showed the stimulation of nodulation parameters and the N
fixation through the native Rhizobium isolates at early stage of common bean plants. Under
field trial conditions, the nodulation, growth parameters and yield were stimulated
significantly for ICA Pijao as compared with BAT-304 upon inoculation with the isolated
Rhizobium strains. Furthermore, genes differentially expressed during the bean root
interaction with Rhizobium etli CNPAF512, infection with Fusarium solani f. sp. phaseoli
and a control respectively, were identified using the cDNA-Amplified Fragment Length
Polymorphism (cDNA-AFLP) technique. In silico analysis was used to determine the
differential expression profiles of transcript derived fragments (TDFs). Several TDFs were
isolated, cloned, sequenced and the obtained DNA sequences were compared with sequences
in the GenBank database. The sequences retrieved revealed homology with genes encoding
stress/defense and cell metabolism functions for Rhizobium treatments, as well as
stress/defense functions for the Fusarium condition.
The results outlined in this study demonstrate the potential of selection for efficient
associations among bean genotypes, rhizobia and plant growth promoting rhizobacteria in
order to achieve the increase of SNF in common bean under local agro-ecosystems, as well as
increase our insight of the molecular dialogue in common bean-rhizobia interaction.
However, these studies should be expanded using more bean genotypes and bacterial
combinations in different environmental conditions, in order to provide recommendations to
farmers.
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Palabras clave
Rhizobium, Phaseolus Vulgaris L., Legumbres, Leguminosae, Frijol