Genetic and phenotypic diversity of Rhizobium isolates from Southern Ecuador

Roldán Torres-Gutiérrez,Klever Iván Granda-Mora,Noroska Gabriela Salazar Mogollón,Aminael Sánchez Rodriguez,José Rafael De Almeida,Yelenys Alvarado-Capó

doi:10.1590/1413-70542017416008517

Abstract

ABSTRACT Rhizobium-legume symbioses play relevant roles in agriculture but have not been well studied in Ecuador. The aim of this study was to characterize the genetic and phenotypic diversity of Rhizobium isolates associated with Phaseolus vulgaris from southern Ecuador. Morpho-cultural characterization, biochemical tests and physiological analyses were conducted to authenticate and determine the diversity of bacteria Rhizobium-like isolates. The genetic diversity of the isolates was determined by molecular techniques, which consisted of bacteria DNA extraction and amplification and sequencing of the 16S rRNA gene. The nodulation parameters and nitrogen fixation for P. vulgaris under greenhouse conditions were also assessed to determine the phenotypic diversity among isolates. Furthermore, bacteria indole-acetic-acid production was evaluated by the colorimetric method. Morpho-cultural and biochemical characteristic assessments demonstrated that Rhizobium-like bacteria was associated with the P. vulgaris nodules. The diversity among the isolates, as determined by physiological analyses, revealed the potential of several isolates to grow at different pH values, salinity conditions and temperatures. Partial sequencing of the 16S rRNA gene identified the Rhizobium genus in every sampling site. From a total of 20 aligned sequences, nine species of Rhizobium were identified. Nodule formation and biomass, as well as nitrogen fixation, showed an increase in plant phenotypic parameters, which could be influenced by IAA production, especially for the strains R. mesoamericanum NAM1 and R. leguminosarum bv. viciae COL6. These results demonstrated the efficiency of native symbiotic diazotrophic strains inoculants for legume production. This work can serve as the basis for additional studies of native Rhizobium strains and to help spread the use of biofertilizers in Ecuadorian fields.

Highlights

The common bean (Phaseolus vulgaris L.) is the most important grain legume worldwide and plays a significant role in human nutrition, being a major source of dietary protein and representing a rich source of minerals and vitamins (Zaccardelli; Pentagelo; Tripodi, 2013)
Beans can carry out biological nitrogen fixation (BNF) through symbiosis with root nodule-associated soil bacteria collectively called rhizobia, which contribute to plant nutrition and allow plants to grow in nitrogen deficient soils (López-Guerrero et al, 2012; Sánchez et al, 2014)
This suggests that Ecuador is the center of genetic diversification for the common bean (Debouck et al, 1993), and symbionts of the several species of Rhizobium should be isolated from this region (Ribeiro et al, 2013)

Summary

Introduction

The common bean (Phaseolus vulgaris L.) is the most important grain legume worldwide and plays a significant role in human nutrition, being a major source of dietary protein and representing a rich source of minerals and vitamins (Zaccardelli; Pentagelo; Tripodi, 2013). Beans can carry out biological nitrogen fixation (BNF) through symbiosis with root nodule-associated soil bacteria collectively called rhizobia, which contribute to plant nutrition and allow plants to grow in nitrogen deficient soils (López-Guerrero et al, 2012; Sánchez et al, 2014). The amount of nitrogen fixed by the common bean in association with rhizobia under field conditions is often low compared to that of other legumes (Remans et al, 2008a). The success of the symbiotic process depends on the competitiveness, specificity, compatibility, and effectiveness of the rhizobia with its host legume under variable soil and environmental conditions (Naveed et al, 2015). One of the major reasons for the low response of this grain legume that it is a highly promiscuous host (Fuentes et al, 2002; Baginsky et al, 2015). The efficiency of nodulation and nitrogen fixation could be influenced by the infection of several rhizobia in the same host (Wei et al, 2008; Ormeño-Orilla; Martínez-Romero, 2013)

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