Symbiotic nitrogen-fixing bacterial populations trapped from soils under agroforestry systems in the Western Amazon

Authors

  • Paula Marcela Duque Jaramillo Universidade Federal de Lavras; Depto de Ciência do Solo
  • Amanda Azarias Guimarães Universidade Federal de Lavras; Depto de Ciência do Solo
  • Ligiane Aparecida Florentino Universidade Federal de Lavras; Depto de Ciência do Solo
  • Karina Barroso Silva Universidade Federal de Lavras; Depto de Ciência do Solo
  • Rafaela Simão Abrahão Nóbrega Universidade Federal de Lavras; Depto de Ciência do Solo
  • Fatima Maria de Souza Moreira Universidade Federal de Lavras; Depto de Ciência do Solo

DOI:

https://doi.org/10.1590/S0103-90162013000600004

Abstract

Cowpea (Vigna unguiculata) is an important grain-producing legume that can forego nitrogen fertilization by establishing an efficient symbiosis with nitrogen-fixing bacteria. Although inoculating strains have already been selected for this species, little is known about the genotypic and symbiotic diversity of native rhizobia. Recently, Bradyrhizobium has been shown to be the genus most frequently trapped by cowpea in agricultural soils of the Amazon region. We investigated the genetic and symbiotic diversity of 148 bacterial strains with different phenotypic and cultural properties isolated from the nodules of the trap species cowpea, which was inoculated with samples from soils under agroforestry systems from the western Amazon. Sixty non-nodulating strains indicated a high frequency of endophytic strains in the nodules. The 88 authenticated strains had varying symbiotic efficiency. The SPAD (Soil Plant Analysis Development) index (indirect measurement of chlorophyll content) was more efficient at evaluating the contribution of symbiotic N2-fixation than shoot dry matter under axenic conditions. Cowpea-nodulating bacteria exhibited a high level of genetic diversity, with 68 genotypes identified by BOX-PCR. Sequencing of the 16S rRNA gene showed a predominance of the genus Bradyrhizobium, which accounted for 70 % of all strains sequenced. Other genera identified were Rhizobium, Ochrobactrum, Paenibacillus, Bosea, Bacillus, Enterobacter, and Stenotrophomonas. These results support the promiscuity of cowpea and demonstrate the high genetic and symbiotic diversity of rhizobia in soils under agroforestry systems, with some strains exhibiting potential for use as inoculants. The predominance of Bradyrhizobium in land uses with different plant communities and soil characteristics reflects the adaptation of this genus to the Amazon region.

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Published

2013-12-01

How to Cite

Jaramillo, P. M. D., Guimarães, A. A., Florentino, L. A., Silva, K. B., Nóbrega, R. S. A., & Moreira, F. M. de S. (2013). Symbiotic nitrogen-fixing bacterial populations trapped from soils under agroforestry systems in the Western Amazon . Scientia Agricola, 70(6), 397-404. https://doi.org/10.1590/S0103-90162013000600004

Issue

Section

Agricultural Microbiology