Variability of isolated colonies in bean nodulating Rhizobium strains before and after exposure to high temperature

Abstract

Irregular response to bean plants to Rhizobium inoculation has been attributed to among other factors, low competitive ability, low N2 fixation efficiency and genetic instability of the symbiont. This genetic instability caused by high rates of genomic rearrangements and/or plasmid deletions can be accentuated by high temperatures. This fact may limit the utilization of these strains as inoculants, especially in tropical soils. In this study, the variability of isolated colonies derived from effective R. leguminosarum bv. phaseoli (SLP1.3 and BR 10.026) and R tropici (SLA2.2 and BR322) strains was evaluated before and after exposure to high temperatures (four consecutive thermal shocks at 45ºC). This evaluation involved plant dry matter analysis of inoculated plants and genotypic (plasmid profile and genomic patterns via RAPD) analysis of the Rhizobium strains. The results evidenced that high temperature improve the natural performance variability especially between isolated colonies from R. leguminosarum bv. phaseoli strains. The plasmid profile of isolated colonies from R. tropici strains were identical regardless of temperature treatment whereas isolated colonies from R. leguminosarum bv. phaseoli alterations were detected especially after the thermal treatment. The genomic patterns generated by AP-PCR showed more alterations and genetic variation in isolated colonies from R. leguminosarum bv. phaseoli strains indicating that R. tropici strains are more stable and lower affected by high temperature.

Genetic diversity of rhizobia in a Brazilian oxisol nodulating Mesoamerican and Andean genotypes of common bean (Phaseolus vulgaris L.)

“…Anyango et al 1995;Andrade et al 2002) and temperature (Raposeiras et al 2002), by the trapping host species (e.g. Leucaena X common bean, Mercante et al 1998;Straliotto et al 1999), and the sampling method (e.g.…”

Effects of plasmid curing on Rhizobium spp.

“…The nodulation (nodABC) genes, the regulatory (nodD) gene and the nitrogen fixing (nif/fix) genes are located on large (usually ≥ 100 kb) symbiotic plasmids (pSym) (5). Plasmid instability in rhizobia where genome rearrangements result in a loss or gain of symbiotic performance has been shown in a number of studies (6). A number of workers found that treatment of rhizobia with plasmid curing agents like acridine orange, acriflavine, UV etc decreased the symbiotic properties nn Received 04 January 2012/Accepted 13 March 2012 of these bacteria, suggesting a link between the nitrogen fixation, nodulation and plasmids (7).…”

Acid tolerant Rhizobium strains contribute to increasing the yield and profitability of common bean in tropical soils

“…Prominent limiting factors include competition of the rhizobium with inefficient native strains established in the soil (Araújo et al, 2007) and adverse environmental conditions, such as high temperature (Raposeiras et al, 2002), soil acidity (Vargas and Graham, 1988), and other soil factors, such as aluminum (Al) and manganese toxicity (Tsai et al, 1993).…”