Soybean-nodulating strains with low intrinsic competitiveness for nodulation, good symbiotic performance, and stress-tolerance isolated from soybean-cropped soils in Argentina
Fecha
2019Autor
Versión
Acceso abierto / Sarbide irekia
Tipo
Artículo / Artikulua
Versión
Versión publicada / Argitaratu den bertsioa
Impacto
|
10.3389/fmicb.2019.01061
Resumen
Soybean is the most important oilseed in the world, cropped in 120–130 million
hectares each year. The three most important soybean producers are Argentina,
Brazil, and United States, where soybean crops are routinely inoculated with symbiotic
N2-fixing Bradyrhizobium spp. This extended inoculation gave rise to soybeannodulating
allochthonous populations (SNAPs) that compete against new inocu ...
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Soybean is the most important oilseed in the world, cropped in 120–130 million
hectares each year. The three most important soybean producers are Argentina,
Brazil, and United States, where soybean crops are routinely inoculated with symbiotic
N2-fixing Bradyrhizobium spp. This extended inoculation gave rise to soybeannodulating
allochthonous populations (SNAPs) that compete against new inoculant for
nodulation, thus impairing yield responses. Competitiveness depends on intrinsic factors
contributed by genotype, extrinsic ones determined by growth and environmental
conditions, and strain persistence in the soil. To assess these factors in Argentinean
SNAPs, we studied 58 isolates from five sites of the main soybean cropping area.
BOX-A1R DNA fingerprint distributed these isolates in 10 clades that paralleled
the pHs of their original soils. By contrast, reference Bradyrhizobium spp. strains,
including those used as soybean-inoculants, were confined to a single clade. More
detailed characterization of a subset of 11 SNAP-isolates revealed that five were
Bradyrhizobium japonicum, two Bradyrhizobium elkanii, two Rhizobium radiobacter
(formerly Agrobacterium tumefaciens), one Bradyrhizobium diazoefficiens, and one
Paenibacillus glycanilyticus, which did not nodulate when inoculated alone, and
therefore was excluded from further characterization. The remaining subset of 10 SNAPisolates
was used for deeper characterization. All SNAP-isolates were aluminum- and
heat-tolerant, and most of them were glyphosate-tolerant. Meanwhile, inoculant strains
tested were sensitive to aluminum and glyphosate. In addition, all SNAP-isolates were
motile to different degrees. Only three SNAP-isolates were deficient for N2-fixation, and
none was intrinsically more competitive than the inoculant strain. These results are in
contrast to the general belief that rhizobia from soil populations evolved as intrinsically
more competitive for nodulation and less N2-fixing effective than inoculants strains. Shoot:root ratios, both as dry biomass and as total N, were highly correlated with
leaf ureide contents, and therefore may be easy indicators of N2-fixing performance,
suggesting that highly effective N2-fixing and well-adapted strains may be readily
selected from SNAPs. In addition, intrinsic competitiveness of the inoculants strains
seems already optimized against SNAP strains, and therefore our efforts to improve
nodules occupation by inoculated strains should focus on the optimization of extrinsic
competitiveness factors, such as inoculant formulation and inoculation technology. [--]
Materias
Bradyrhizobium,
Allochthonous population,
N2-fixation,
Inoculant,
Nodulation
Editor
Frontiers Media
Publicado en
Frontiers in Microbiology
Departamento
Universidad Pública de Navarra/Nafarroako Unibertsitate Publikoa. Institute for Multidisciplinary Research in Applied Biology - IMAB
Versión del editor
Entidades Financiadoras
This work was supported by Agencia Nacional de Promoción
Científica y Tecnológica (ANPCyT) grant number
PICT2013-2542, and Consejo Nacional de Investigaciones
Científicas y Técnicas (CONICET) grant number PIP 0386,
both from Argentina.
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