Diversity of root nodule bacteria isolated from common bean (Phaseolus vulgaris L.) in Cuba: effect of Rhizobium – PGPR inoculation and IAA synthesis on development of bean genotypes
Fecha
2014-12-06
Autores
Colás Sánchez, Ariany
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Universidad Central “Marta Abreu” de Las Villas. Facultad de Ciencias Agropecuarias. Departamento de Agronomía
Resumen
Common bean (Phaseolus vulgaris L.) is the most important food legume for the direct
human consumption in the world and particularly in many parts of Latin America and
Africa. Symbiotic nitrogen fixation (SNF) through association with root-nodulating
rhizobia effectively contributes to an improved crop production and is an ecologically
sound and low cost strategy to improve productivity in common bean cultivation.
However, the amount of nitrogen fix by common bean in the field is often low compared
to the SNF capacity of beans under optimal conditions and compared to other legumes.
The success of SNF in bean cultivation is strongly influenced by prevailing
environmental conditions. Further research to improve the efficiency and stability of
SNF in bean cultivation is needed. In the rhizosphere and in their interaction with plants,
rhizobia encounter many different plant compounds, including phytohormones like
auxins, giberelinis and cytokinins. Several steps of rhizobia-legume interaction are
monitored by these phytohormones, especially nodule formation. However, the exact
role of bacterial IAA (indole-3-acetic acid) in nodule formation and functioning is still
unknown. This study focuses on the characterization of the nodule inhabiting organisms
by the application of molecular techniques and to investigate the agronomic implication
of the legume-Rhizobium-Plant growth promoting rhizobacteria (PGPR), as well as to
determine the possible role of bacterial IAA production in modulation of nodulation.
In total, 20 gram negative strains were isolated from root nodules of common bean in
the central region of Cuba. By partial sequencing of the 16S rRNA gene, six different
genera, i.e. Arthrobacter, Chryseobacterium, Enterobacter, Stenotrophomonas,
Pseudomonas and Rhizobium were recovered. Rhizobium was the only genus containing
differences at the species level. In total four Rhizobium species were identified
(Rhizobium sp., R. etli, R. pisi and R. radiobacter). Of which, only R. pisi and R. etli species
nodulated the host plant. The phenotypic characterization showed the beneficial effect
of the R. etli and R. pisi on bean genotypes, by increasing the nodulation, growth
parameters and N fixation at early stage of common bean plants. Under field trial
conditions, the nodulation, growth parameters and yield were stimulated significantly
for BAT-477 as compared with the genotypes BAT-304, ICA Pijao and DOR-364, upon
Summary
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inoculation with the isolated Rhizobium strains. A survey among 60 local bean farmers
showed that farmers use microbial inocula as well as other organic fertilizers when they
have access to them. Resistance to pests, good taste which was always associated to
black color and resistance to diseases, were included as preferential characteristic for
choosing a new variety.
Combinations of Rhizobium-PGPR were evaluated under different growth conditions,
using two contrasting genotypes (BAT-477 and DOR-364). The results highlight the
interaction between genotype, bacterial inoculant and environmental soil conditions. It
was observed that native Rhizobium-Pseudomonas co-inoculation as compared to single
Rhizobium inoculation increased the nodulation and growth parameters in greenhouse
experiments as well as in a field trials. The combination Rhizobium-Pseudomonas
showed the best results in yield in both genotypes and BAT-477 performed significantly
better than DOR-364. In addition, all nodule endophytic bacterial strains showed plant
growth promoting activities, the production of indole-3-acetic acid (IAA) resulted
common to all of them, the synthesis of siderophores and phosphate solubilization was
only produced for Pseudomonas strains. These results indicate a potential role of
isolated bacterial in improving plant growth. Several lines of evidence suggest a role for
phytohormones in root nodule development. In our study R. pisi R40983 (ipdC)
transconjugant showed major nodule stimulation in common bean plants as well as
major IAA production principally during the stationary growth phase. Based on the
nodulation experiment, it was demonstrated that the introduction of these recombinant
ipdC construct could improve nodulation. These findings contribute to the
understanding of the interplay between Rhizobium, PGPR and the plant host under
different soil conditions. Importantly, co-inoculation with R. pisi and P. monteilii could be
an effective biofertilization strategy for common bean production. From this study, some
important recommendations can be drawn on how to improve bean productivity in this
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Palabras clave
Rhizobium, Phaseolus Vulgaris L., Frijol, Bacterias fijadoras de Nitrógeno