Fast and reliable strain identification methods are needed for studying Bradyrhizobium japonicum field population as well as for the selection the most efficient strains for commercial inoculant production. The main aim of the present investigation was to compare different methods for identification of indigenous B. japonicum strains isolated from different soil types in western Slavonia. Physiological tests, intrinsic antibiotic resistance, SDS-PAGE (sodium dodecil sulphate polyacrilamide gel electrophoresis) of total cell proteins and RAPD (random amplified polymorphic DNA) analysis were used for strain identification and the assessment of variability within natural B. japonicum population. The results of each method were converted to two-dimensional binary matrix and dendrograms, showing relative similarity among B. japonicum strains, were obtained by using biostatistical NTSYS programe. The results showed that among all the methods used in this work, that RAPD analysis was the most sensitive and reliable for strain identification. The lowest level of differentiation among B. japonicum strains were determined by using intrinsic antibiotic resistance. All the methods used in this work, with the exception of intrinsic antibiotic resistance, revealed that all field isolates essentially differed from commercial strains and so can be regarded as indigenous strains for that area. Protein and RAPD profiles very clearly indicated that among natural field population two highly divergent group of strains can be determined.

Bradyrhizobium japonicum; indigenous strains; nitrogen fixation; strain identification

Published by University of Zagreb, Faculty of Agriculture, Zagreb, CROATIA
Sponsored by Ministry Science and Education of the Republic of Croatia