Diversity of Bradyrhizobium strains isolated from root nodules of the shrubby legume Cytisus villosus growing in the Moroccan Rif

The genotypic and phenotypic diversity of nineteen bradyrhizobial strains isolated from the root nodules of wild-grown Cytisus villosus in the central-western region of the Moroccan Rif were carried out. PCR-based RFLP (restriction fragment length polymorphism) of the 16S rDNA (ARDRA) of 19 strains using the restriction enzymes AluI, CfoI, DdeI, HinfI, MspI and RsaI showed that they grouped in 3 clusters. The cluster I includes the type strain Bradyrhizobium canariense BTA-1, the cluster II the type strain Bradyrhizobium japonicum USDA6 and the cluster III the type strains Bradyrhizobium cytisi CTAW11 and Bradyrhizobium rifense CTAW71. The results from 63 physiological and biochemical tests confirmed the existence of the B. canariense and the B. japonicum groups but also allowed the separation of the B. cytisi and B. rifense strains in two groups. The phenotypic characteristics analysed permitted description of a wide physiological and biochemical diversity among the strains, and showed that the heavy metals resistance test was the most discriminating characteristic.