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de Souza R.,Federal University of Rio Grande do Sul | Schoenfeld R.,Instituto Riograndense do Arroz IRGA | Passaglia L.M.P.,Federal University of Rio Grande do Sul
Archives of Agronomy and Soil Science | Year: 2016

Beneficial soil bacteria are able to colonize plant root systems promoting plant growth and increasing crop yield and nutrient uptake through a variety of mechanisms. These bacteria can be an alternative to chemical fertilizers without productivity loss. The objectives of this study were to test bacterial inoculants for their ability to promote nutrient uptake and/or plant growth of rice plants subjected to different rates of chemical fertilizer, and to determine whether inoculants could be an alternative to nitrogen fertilizers. To test the interaction between putatively beneficial bacteria and rice plants, field experiments were conducted with two isolates: AC32 (Herbaspirillum sp.) and UR51 (Rhizobium sp.), and different nitrogen fertilization conditions (0%, 50%, and 100% of urea). Satisfactory results were obtained in relation to the nutrient uptake by plants inoculated with both isolates, principally when the recommended amount of nitrogen fertilizer was 50% reduced. These bacterial strains were unable to increase plant growth and grain yield when plants were subjected to the high level of fertilization. This study indicated that the tested inoculant formulations can provide essential nutrients to plants, especially when the levels of nitrogen fertilizers are reduced. © 2015 Taylor & Francis.

de Souza R.,Federal University of Rio Grande do Sul | Beneduzi A.,Fundacao Estadual de Pesquisa Agropecuaria FEPAGRO | Ambrosini A.,Federal University of Rio Grande do Sul | da Costa P.B.,Federal University of Rio Grande do Sul | And 4 more authors.
Plant and Soil | Year: 2013

Background and Aims: Several strains of rhizobacteria may be found in the rhizospheric soil, on the root surface or in association with rice plants. These bacteria are able to colonize plant root systems and promote plant growth and crop yield through a variety of mechanisms. The objectives of this study were to isolate, identify, and characterize putative plant growth-promoting rhizobacteria (PGPR) associated with rice cropped in different areas of southern Brazil. Methods: Bacterial strains were selectively isolated based on their growth on three selective semi-solid nitrogen-free media. Bacteria were identified at the genus level by PCR-RFLP 16S rRNA gene analysis and partial sequencing methodologies. Bacterial isolates were evaluated for their ability to produce indolic compounds and siderophores and to solubilize phosphate. In vitro biological nitrogen fixation and the ability to produce 1-aminocyclopropane-1-carboxylate deaminase were evaluated for each bacterial isolate used in the inoculation experiments. Results: In total, 336 bacterial strains were isolated representing 31 different bacterial genera. Strains belonging to the genera Agrobacterium, Burkholderia, Enterobacter, and Pseudomonas were the most prominent isolates. Siderophore and indolic compounds producers were widely found among isolates, but 101 isolates were able to solubilize phosphate. Under gnotobiotic conditions, eight isolates were able to stimulate the growth of rice plants. Five of these eight isolates were also field tested in rice plants subjected to different nitrogen fertilization rates. Conclusions: The results showed that the condition of half-fertilization plus separate inoculation with the isolates AC32 (Herbaspirillum sp.), AG15 (Burkholderia sp.), CA21 (Pseudacidovorax sp.), and UR51 (Azospirillum sp.) achieved rice growth similar to those achieved by full-fertilization without inoculation, thus highlighting the potential of these strains for formulating new bioinoculants for rice crops. © 2012 Springer Science+Business Media B.V.

da Costa P.B.,Federal University of Rio Grande do Sul | Beneduzi A.,Fundacao Estadual de Pesquisa Agropecuaria FEPAGRO | de Souza R.,Federal University of Rio Grande do Sul | Schoenfeld R.,Instituto Riograndense do Arroz IRGA | And 2 more authors.
Plant and Soil | Year: 2013

Aims: In this work, the effects of fertilization on diazotroph diversity and plant growth promoting traits were analyzed. An interaction model was then suggested and tested in field. Methods: One hundred and ninety bacterial strains were isolated from rhizospheric soil and roots of rice cropped in three different fertilization conditions. Phosphate solubilization, indolic compound (IC) and siderophore production, and nitrogen fixation abilities of the isolates were screened and compared. Some isolates were selected for in vivo plant growth promotion in greenhouse and field experiments. Results: We found that fertilization had a limited effect on diversity but had a major effect on phosphate solubilization and IC production abilities. We demonstrated that plants select bacteria that present good phosphate solubilization ability for intimate root association in lieu of good IC production under nutrient-poor conditions and select good IC producers in lieu of good phosphate solubilizers under nutrient-moderate conditions. In nutrient-rich conditions, this selection preference seems to be deactivated. In the field trial, good phosphate solubilizers only contributed effectively to plant growth at nutrient-poor conditions and good IC producers only contributed to plant growth at nutrient-moderate conditions. Conclusions: Fertilization affects the PGP traits of the diazotrophic community. These findings may be used for directed PGPR prospection and anticipated PGPR candidate selection. © 2012 Springer Science+Business Media Dordrecht.

Dors G.C.,Grande Rio University | Caldas S.S.,Grande Rio University | Dos Santos Hackbart H.C.,Grande Rio University | Primel E.G.,Grande Rio University | And 2 more authors.
Journal of Agricultural and Food Chemistry | Year: 2013

This study aimed to evaluate the effect of fungicides on rice cultivation, regarding the occurrence and the distribution of mycotoxins in fractions of the processed grain, by a validated chromatographic method. A method based on extraction with acetonitrile:water, determination by HPLC-DAD, and confirmation by LC-MS was validated before the mycotoxin evaluation. Control samples and samples to which triazole fungicides had been applied were collected from experimental fields for four years. Results showed that 87% of the samples were contaminated with deoxynivalenol or zearalenone, and that all samples treated with fungicide were contaminated with some of these mycotoxins. Aflatoxin B 1 and ochratoxin A were found in 37% of the samples; half of them had been treated with fungicide. Therefore, fungicides tend to be stressors for toxigenic fungi found in the fields. © 2013 American Chemical Society.

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