Strain selection for improvement of Bradyrhizobium japonicum competitiveness for nodulation of soybean

MARÍA JULIA ALTHABEGOITI; SILVINA L. LÓPEZ-GARCÍA; CARLOS PICCINETTI; ELÍAS J. MONGIARDINI; JULIETA PÉREZ-GIMENEZ; JUAN IGNACIO QUELAS; ALEJANDRO PERTICARI; ANÍBAL R. LODEIRO

FEMS MICROBIOLOGY LETTERS

Blackwell Publishing Ltd

Lugar: Hoboken, New Jersey; Año: 2008 vol. 282 p. 115 - 123

0378-1097

A Bradyrhizobium japonicum USDA 110-derived strain able to produce wider halosin soft-agar medium than its parental strain was obtained by recurrent selection. Itwas more chemotactic than the wild type towards mannitol and three amino acids.When cultured in minimal medium with mannitol as a single carbon-source, ithad one thick subpolar flagellum as the wild type, plus several other flagella thatwere thinner and sinusoidal. Root adsorption and infectivity in liquid media were50–100% higher for the selected strain, but root colonization in water-unsaturatedvermiculite was similar to the wild type. A field experiment was then carried out ina soil with a naturalized population of 1.8105 soybean-nodulating rhizobia g ofsoil1. Bradyrhizobium japonicum strains were inoculated either on the soybeanseeds or in the sowing furrows. Nodule occupation was doubled when the strainswere inoculated in the sowing furrows with respect to seed inoculation (significantwith Po0.05). On comparing strains, nodule occupation with seed inoculationwas 6% or 10% for the wild type or selected strains, respectively, without astatistically significant difference, while when inoculated in the sowing furrows,nodule occupation increased to 12% and 22%, respectively (differences significantwith Po0.05)