Abstract
The aim of this work was to characterize and to describe the diversity and phylogeny of rhizobial bacteria associated to nodules of faba bean in four different geographical regions of north Egypt. Eight rhizobial isolates from healthy faba bean roots were isolated. They were identified as Rhizobium leguminosarum morphologically. They showed sensitivity to Kanamycin, Neomycin and Sulphemethooxazole antibiotics. Mannitol was the best source of carbon source for their growth. However, two isolates Rl. 2 and Rl. 10 indicated better tolerance to high NaCl concentrations than the other isolates and their plasmid profiles contained additional large plasmid with molecular weight about 23 kb. A relationship between salt tolerance and extra plasmid was suggested. Analysis of similarity among rhizobial isolates by using the RAPD-PCR technique showed a high level of genetic polymorphism, grouping the rhizobial isolates into two different clusters. These clusters reflexed the similarity among genotype of isolates independent of their geographic locations. 16S rDNA sequences of three representing isolates were determined and were aligned and compared with the 16S rDNA sequences of other members of the family Rhizobiaceae available in the Gene Bank database. The obtained dendogram indicated that the isolates belonging to Rhizobium leguminosarum biovar viciaen.
Highlights
Bacteria belonging to the genera Allorhizobium, Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium and Sinorhizobium are generally called rhizobia [1]
It is well known that crop plants belonging to the genera Vicia, Lathyrus, Pisum and Lens are effectively nodulated by isolates of Rhizobium leguminosarum biovar viciae [4]
This study have mainly focused on the assessment of rhizobial diversity and characterization of native rhizobial isolates from different areas in north Egypt, compared them for their potential use in salinity soil by a polyphasic approach including the evaluation of biochemical properties as well as molecular characteristics
Summary
Bacteria belonging to the genera Allorhizobium, Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium and Sinorhizobium are generally called rhizobia [1]. Legume roots and seeds exude a number of organic compounds (e.g. flavonoids), which differ between species [5] Rhizobia respond to these by one or more of the constitutive genes called Nod Factors [6]. Nutrient uptake and metabolism, and protein synthesis are all thought to be adversely affected by salt stress conditions [9] All these factors lead to unsuccessful legume nodulation [10]. The development and increased availability of molecular biology techniques have made it possible to obtain information regarding the genomic organization and diversity of rhizobia populations in different soils [11]. This study have mainly focused on the assessment of rhizobial diversity and characterization of native rhizobial isolates from different areas in north Egypt, compared them for their potential use in salinity soil by a polyphasic approach including the evaluation of biochemical properties as well as molecular characteristics
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