Verification of strain identity in Brazilian soybean inoculants by using the Polymerase Chain Reaction

Abstract

The standards for meeting inoculant quality in Brazil include a requirement of strain verification as well as the necessity for a minimal number of viable bacterial cells. This requirement stimulated us to develop a rapid and simple PCR-based method to distinguish the four Brazilian strains of Bradyrhizobium, SEMIA 587, SEMIA 5019 (29W), SEMIA 5079 (CPAC-15) and SEMIA 5080 (CPAC-7), recommended for the inoculation of soybean. PCR reactions using the random amplified polymorphic DNA (RAPD) PCR primer CRL-7 together with a modified buffer resulted in four different fingerprint patterns, which permitted the Brazilian soybean strains to be distinguished from each other. The fingerprint patterns obtained were reproducible irrespective of the source of templates. Comparisons with fingerprint patterns obtained with soybean bradyrhizobia from the USDA Culture Collection led to the conclusion that two of the Brazilian inoculant strains (SEMIA 587 and SEMIA 5019) were characteristic for B. elkanii, while the other two (SEMIA 5079 and SEMIA 5080) were more typical of B. japonicum. Also, we obtained evidence that the RAPD analysis with primer CRL-7 may be useful for distinguishing variants of the same strain.