Evaluation of bradyrhizobia strains isolated from field-grown soybean plants in Argentina as improved inoculants

Bradyrhizobium strains were isolated from nodules obtained from field-grown soybean plants sampled in 12 soybean production locations in Argentina. These fields had been annually cropped with soybean and did not show decreases in yields even though they had been neither N-fertilized nor inoculated for at least the last 5 years. We hypothesized that the isolated strains maintained high competitiveness and efficiency in fixing adequate N2 levels. A set of strains that showed the highest nodular occupancy in each sampling location were assayed for symbiotic performance under greenhouse and field conditions and comparatively evaluated with Bradyrhizobium japonicum E109, the strain officially recommended for inoculant formulation in Argentina. An inoculant pool, formed by four strains obtained from nodules collected from Cañada Rica, developed higher nodular biomass than B. japonicum E 109 in assays carried out in greenhouses under well irrigated conditions. Additionally, neither nodule production nor specific nitrogenase activity decreased with respect to B. japonicum E 109 when plants were drought stressed during 7 days from sowing. The mean yields obtained under field conditions and plotted against the principal component one (CP1) obtained with an additive main effect and multiplicative interaction (AMMI) model showed that the inoculant pool from Cañada Rica had higher contribution to yield than strain E 109, although with lower environmental stability. The inoculant pool from Cañada Rica could be considered an improved inoculant and be used for preliminary assays, to formulate inoculants in Argentina. © 2010 Springer-Verlag.Fil: Melchiorre, Mariana Noemi. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Unidad de Estudios Agropecuarios - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Unidad de Estudios Agropecuarios; ArgentinaFil: de Luca, Marcos Javier. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Fitopatología y Fisiología Vegetal; ArgentinaFil: González Anta, Gustavo Gabriel. Universidad Nacional del Noroeste de la Provincia de Buenos Aires; ArgentinaFil: Suarez, Paola. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Fitopatología y Fisiología Vegetal; ArgentinaFil: Lopez, Carlos. Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Cordoba. Estacion Experimental Agropecuaria Manfredi. Agencia de Extension Rural Rio Primero.; ArgentinaFil: Lascano, Hernan Ramiro. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Unidad de Estudios Agropecuarios - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Unidad de Estudios Agropecuarios; ArgentinaFil: Racca, Roberto Walter. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Fitopatología y Fisiología Vegetal; Argentin

Biocontrol potential index of pseudomonads, instead of their direct-growth promotion traits, is a predictor of seed inoculation effect on crop productivity under field conditions

Agricultural bioproducts became interesting alternatives for sustainable agricultural practices, because they aim to reduce the use of agrochemicals without losing crop yields. As Pseudomonas genus has been largely studied for the high number of plant probiotic species it contains, in this work we evaluated the field performance of 10 genetically diverse native Pseudomonas that have been isolated from productive plots of the Argentine Pampas. Previously, they have been characterized in vitro, and we have developed several indexes to organize the isolates’ collection based on their potential to perform biocontrol of fungal pathogens (BPI), to promote plant growth by direct mechanisms (DGPI), or by integrated direct plus indirect mechanisms (PGPI). At three geographical sites, we tested the effect of single- and co-inoculations with a commercial bio-input based on the fungus Trichoderma harzianum Th2, in wheat and maize crops during 3 consecutive seasons. Most of single inoculations improved wheat and maize grain yields. For wheat, improvement seemed to be related with a higher plant emergence by the positive correlation between yield and plant number; whereas for maize increased yields would be rather associated with a better plant structure by the positive correlation between yield and the vegetation index NDVI. The co-inoculation of Th2 with different P. chlororaphis isolates also increased the grain yield of both grain crops, despite P. chlororaphis strains displayed fungal inhibition in dual culture in vitro tests. We found a positive and significant correlation between BPI and the yield percentage improvement of both crops, but a negative correlation with DGPI. Thus, this work shows the usefulness of the in vitro characterization of biocontrol-related traits and the estimation of a biocontrol potential index as a proxy for crop yield performance, but not of direct plant growth-promoting features.Fil: Agaras, Betina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Noguera, Fabián. No especifíca;Fil: González Anta, Gustavo Gabriel. Universidad Nacional del Noroeste de la Provincia de Buenos Aires; ArgentinaFil: Wall, Luis Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Valverde, Claudio Fabián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; Argentin