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vol.33 issue5Microbial alterations of the soil influenced by induced compactionOccurrence of plant growth-promoting traits in clover-nodulating rhizobia strains isolated from different soils in Rio Grande do Sul state author indexsubject indexarticles search
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Revista Brasileira de Ciência do Solo

On-line version ISSN 1806-9657

Abstract

LEITE, Jakson et al. Biodiversity of rhizobia associated with cowpea cultivars in soils of the lower half of the São Francisco River Valley. Rev. Bras. Ciênc. Solo [online]. 2009, vol.33, n.5, pp.1215-1226. ISSN 1806-9657.  http://dx.doi.org/10.1590/S0100-06832009000500015.

The biodiversity of rhizobium in soils of the São Francisco Valley is unknown and can be studied using cowpea as trap plants. The objective of this study was to verify the diversity of diazotrophic bacteria that nodulate cowpea in soils of the lower half of the São Francisco River Valley by morphological and genotypic characterization. Seven soil samples (A1, A2, A3, A4, C1, C2 and MC) were collected to capture bacteria associated to five cowpea cultivars (IPA 206, BRS Pujante, BRS Marataoã, Canapu Roxo, and Sempre Verde), in a 5x7 factorial design with three replications. Thirty days after plant emergence, the nodules were collected and the bacteria isolated and analyzed in relation to their growth characteristics in YMA medium. The 581 isolates were grouped in 49 morphologic groups. Of this total, 62.3 % formed colonies in up to three days, 33.4 % grew from the 6th day on, and 4.3 % began to grow 4 to 5 days after incubation. Regarding the formation of acids and alkalis, 63 % acidified the medium, 12 % made it alkaline and 25 % maintained the medium at neutral pH. The highest diversity was observed in the A3 sample and in isolates associated with the cultivars Canapu Roxo and BRS Pujante. Thirty-eight representative isolates were chosen for the genotypic characterization, clustered in four groups based on the restriction analysis of 16s rDNA. This grouping was strongly correlated with the sampling site; 13 rhizobium isolates had an electrophoretic profile distinct from the standard rhizobium strains used in this study.

Keywords : ARDRA; biological nitrogen fixation; Vigna unguiculata.

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