Assessment of cowpea rhizobium diversity in Cerrado areas of northeastern Brazil

In order to contribute for the optimization of biological nitrogen fixation (BNF) associated with cowpea in Cerrado areas in the Northeast region of Brazil, this work aimed to analyze the diversity of rhizobial populations in eight areas of Cerrado, during a soybean and rice-cowpea rotation. Morphol...

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Published in:Brazilian journal of microbiology 2004-12, Vol.35 (4), p.281-287
Main Authors: Zilli, Jerri Édson(IEmbrapa Roraima), Valisheski, Romano Roberto(Universidade Estadual do Norte Fluminense), Freire Filho, Francisco Rodrigues(Embrapa Meio-Norte), Neves, Maria Cristina Prata(Embrapa Meio-Norte), Rumjanek, Norma Gouvêa(Embrapa Meio-Norte)
Format: Article
Language:eng ; por
Subjects:
antibiotic
Bradyrhizobium
Bradyrhizobium elkanii
caupi
Cerrado
cowpea
diversidade
diversity
MICROBIOLOGY
resistência a antibiótico
Rhizobium
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Summary:In order to contribute for the optimization of biological nitrogen fixation (BNF) associated with cowpea in Cerrado areas in the Northeast region of Brazil, this work aimed to analyze the diversity of rhizobial populations in eight areas of Cerrado, during a soybean and rice-cowpea rotation. Morphological traits (mucous production and colony morphology), genotypic analyzes (ARDRA 16S) and intrinsic resistance to antibiotics were determined for a collection of isolates captured using cowpea as a host-plant. The morphological data showed a inverse correlation (p < 0.05) between the number of legume (soybean and cowpea) crops, according to the history of each area, and rhizobium diversity, estimated by the Shannon-Weaver index. ARDRA data showed that native Cerrado areas were exclusively colonized by Bradyrhizobium elkanii, corroborating previous data. In the areas where legumes were grown, we observed two distinct situations: where soybean only were grown, a high proportion of B. japonicum was found, and where soybean and cowpea were grown, we observed more B. elkanii. The analysis of antibiotic resistance revealed five different profiles. High percentage of antibiotic resistant Bradyrhizobium spp. isolates were found in the areas cultivated for a long time, whereas the native area and areas with a few crops had fewer resistant strain. There was an inverse relationship between intrinsic antibiotic resistance and rhizobial diversity, while the last decreases as more legume crops are introduced into the area, the former increases, suggesting that the presence of legumes may provide ecological conditions to select specific rhizobium groups, which acquire competitiveness traits and become successfully established. Com o objetivo de contribuir com a otimização do processo de fixação biológica de nitrogênio (FBN) na cultura do caupi (Vigna unguiculata (L) Walp) no Cerrado do nordeste brasileiro, a diversidade de isolados de rizóbio obtidos em oito áreas de Cerrado com rotação de cultura bianual com soja, arroz e caupi. Foram realizadas caracterizações morfológicas (produção de muco e morfologia das colônias), genotípicas baseadas em ARDRA do 16S rDNA e resistência a antibióticos. Os resultados da caracterização morfológica mostraram uma correlação inversamente proporcional (p < 0,05) do índice de diversidade de Shannon-Waver com o número de cultivos de leguminosas (caupi e soja). Os dados de ARDRA mostraram que no Cerrado nativo somente foram observados isolados d
ISSN:1517-8382
1678-4405
1678-4405
DOI:10.1590/s1517-83822004000300002