engleski

Genomic Fingerprinting of Indigenous Soybean Rhizobia

The presence of adapted and competitive indigenous soybean rhizobia in soil can reduce the inoculation response even with the highly efficient commercial strains. On the other hand, the studying of rhizobial biodiversity opens up the possibility to preserve and maybe to exploitate some indigenous strains with hidden symbiotic or ecological potential, particularly under unfavourable conditions. In this respect, it is important to characterize the indigenous strains and to obtain information about actual composition of rhizobial field population. The main aim of the present study was to isolate and to identify indigenous Bradyrhizobium japonicum strains isolated from different soybean growing areas in Croatia and to detect genetic diversity within rhizobial natural populations. All rhizobial isolates were characterized by using different PCR fingerprinting methods such as 16S rDNA PCR-RFLP and RAPD analysis. PCR-RFLP of 16S rDNA clearly showed that all isolates can be determined as Bradyrhizobium japonicum. Cluster analysis of combined RFLP patterns obtained with three restriction endonucleases, revealed that all soybean isolates were identical with B. japonicum type and reference strains as well as with B. lioaningense type strain while they significantly differed from B. elkanii and S. fredi type strains. After the identification at the species level, all isolates and reference strains were further characterized by RAPD analysis that enabled differentiation at the strain level. Total genomic DNAs from 17 field isolates and four reference strains were amplified using four different 10-mer primers. Amplification reactions with four randomly chosen primers, generated highly specific and reproducible patterns which enabled strain differentiation. RAPD profiles revealed that all field isolates considerably differed from reference strains. Cluster analysis showed high degree of diversity among field isolates. None of the strains were identical or nealrly identical to each other. Dendrogram derived from RAPD profiles showed that all indigenous strains could be divided into three main groups. Although dependency upon grouping and origin of isolates was not determined, the higher level of diversity was determined among the several strains obtained from region where soybean has been recently introduced.

rhizobial biodiversity; Bradyrhizobium japonicum; PCR fingerprinting

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