The Diversity of Phaseolus -Nodulating Rhizobial Populations Is Altered by Liming of Acid Soils Planted with Phaseolus vulgaris L. in Brazil

Abstract

PCR-mediated restriction fragment length polymorphism (RFLP) analysis of the 16S-23S rRNA internally transcribed spacer (ITS) region and the 16S rRNA gene indicated that the rhizobial populations isolated from common bean (Phaseolus vulgaris L.) nodules in the unlimed soil from a series of five lime rates applied 6 years previously to plots of an acidic oxisol had less diversity than those from plots with higher rates of liming. Isolates affiliated with Rhizobium tropici IIB and Rhizobium leguminosarum bv. phaseoli were predominant independent of lime application. An index of richness based on the number of ITS groups increased from 2.2 to 5.7 along the soil liming gradient, and the richness index based on "species" types determined by RFLP analysis of the 16S rRNA gene varied from 0.5 to 1.4. The Shannon index of diversity, based on the number of ITS groups, increased from 1.8 in unlimed soil to 2.8 in limed soil, and, based on RFLP analysis of the 16S rRNA gene, ranged from 0.9 to 1.4. In the limed soil, the subpopulation of R. tropici IIB pattern types contained the largest number of ITS groups. In contrast, there were more R. leguminosarum bv. phaseoli types in the unlimed soil with the lowest pH than in soils with the highest pH. The number of ITS ("strain") groups within R. leguminosarum bv. phaseoli did not change with increased abundance of rhizobia in the soil, while with R. tropici IIB, the number of strain groups increased significantly. Some cultural and biochemical characteristics of Phaseolus-nodulating isolates were significantly related to changes in soil properties caused by liming, largely due to changes in the predominance of the rhizobial species groups.

Genetic and phenotypic diversity of Rhizobium isolates from Southern Ecuador

“…In the present study, the physiological characterization showed a high tolerance of the strains COL6, CB1 and SOS1 to grow at different pH values, salinity conditions and temperatures. Similar results reported by Andrade, Murphy and Giller (2002) and Shamseldin and Werner (2005) as well as the predominant R. tropici, which nodulates P. vulgaris in southern Ecuador (Table 4). Although few studies have reported on the genetic diversity of Rhizobium in Ecuador (Ribeiro et al, 2013), this is the first report of species diversity in the southern region of the country.…”

Genetic characterization and nitrogen fixation capacity of Rhizobium strains on common bean

“…This result may explain the presence of the species R. tropici (LBMP-4BR) in a soil with corn monoculture in minimum tillage (Table 1). However, Andrade et al (2002) observed a predominance of R. leguminosarum in acid soils that were not treated with lime. This is similar to results found in this study, as LBMP-3VE was isolated from acidic soil with no lime application.…”

The effect of biotic and physical factors on the competitive ability of Rhizobium leguminosarum

“…Vegetative forms of bacteria multiply in the infection threads and saprophytic zones of indeterminate type nodules, and are released into the soil during the decay of nodules [4,5]. Amongst the heterogeneous microbial communities in the soil, rhizobia constitute numerous and very differentiated populations [6][7][8][9][10]. Several factors can influence the number and diversity of indigenous rhizobia, including nutrient availability, soil type, acidity and agricultural management regimes [6,11,12].…”