IBBM   21076
INSTITUTO DE BIOTECNOLOGIA Y BIOLOGIA MOLECULAR
Unidad Ejecutora - UE
artículos
Título:
Soybean-Nodulating Strains With Low Intrinsic Competitiveness for Nodulation, Good Symbiotic Performance, and Stress-Tolerance Isolated From Soybean-Cropped Soils in Argentina
Autor/es:
ITURRALDE, ESTEBAN T.; PÉREZ-GIMÉNEZ, JULIETA; COVELLI, JULIETA M.; ARRESE-IGOR, CESAR; ALVAREZ, FLORENCIA; LODEIRO, ANÍBAL R.
Revista:
Frontiers in Microbiology
Editorial:
Frontiers Media S.A.
Referencias:
Año: 2019 vol. 10
Resumen:
Soybean is the most important oilseed in the world, being cropped in120-130 million hectares each year. The three most important soybean producersare Argentina, Brazil, and USA, where soybean crops are routinely inoculated withsymbiotic N2-fixing Bradyrhizobiumspp. This extended inoculation gave rise to soybean-nodulating allochthonouspopulations (SNAPs) that compete against new inoculant for nodulation, thus impairingyield responses. Competitiveness depends on intrinsic factors contributed by genotype,extrinsic ones determined by growth and environmental conditions, and strain persistencein the soil. To assess these factors in Argentinean SNAPs, we studied 58isolates from five sites of the main soybean cropping area. BOX-A1R DNAfingerprint distributed these isolates in 10 clades that paralleled the pHs of theiroriginal soils. By contrast, reference Bradyrhizobiumspp strains, including those used as soybean-inoculants, were confined to asingle clade. More detailed characterization of a subset of 11 SNAP-isolates revealedthat five were B. japonicum, two B. elkanii, two Rhizobium radiobacter (formerly Agrobacteriumtumefaciens), one B. diazoefficiens,and one Paenibacillus glycanilyticus¾which did not nodulate when inoculated alone, andtherefore was excluded from further characterization.Theremaining subset of 10 SNAP-isolates was used for deeper characterization. Whileinoculant strains tested were heat-tolerant, and sensitive to aluminium andglyphosate, all SNAP-isolates were aluminium- and heat-tolerant, and most ofthem were glyphosate-tolerant. In addition, all SNAP-isolates were motile todifferent degrees. Only three SNAP-isolates were deficient for N2-fixation,and none was intrinsically more competitive than the inoculant strain. Theseresults are in contrast to the general belief that rhizobia from soilpopulations evolved as intrinsically more competitive for nodulation and less N2-fixingeffective than inoculants strains. Shoot:root ratios, both as dry biomass andas total N, were highly correlated with leaf ureide contents, and therefore maybe easy indicators of N2-fixing performance, suggesting that highlyeffective N2-fixing and well-adapted strains may be readily selectedfrom SNAPs. In addition, intrinsic competitiveness of the inoculants strainsseems already optimized against SNAP strains, and therefore our efforts toimprove nodules occupation by inoculated strains should focus on theoptimization of extrinsic competitiveness factors, such as inoculantformulation and inoculation technology.