The Symbiotic Requirements of Different Medicago Spp. Suggest the Evolution of Sinorhizobium Meliloti and S. Medicae with Hosts Differentially Adapted to Soil pH
Document Type
Article
Publication Date
10-2005
Journal Title
Plant and Soil
ISSN
0032-079X eISSN: 1573-5036
Keywords
acid adaptation, Medicago spp., Sinorhizobium medicae, S. meliloti, symbiotic requirements
Disciplines
Agronomy and Crop Sciences
Abstract
Nitrogen fixing rhizobia associated with the Medicago L. genus belong to two closely related species Sinorhizobium medicae and S. meliloti. To investigate the symbiotic requirements of different Medicago species for the two microsymbionts, 39 bacterial isolates from nodules of eleven Medicago species growing in their natural habitats in the Mediterranean basin plus six historical Australian commercial inocula were symbiotically characterized with Medicago hosts. The bacterial species allocation was first assigned on the basis of symbiotic proficiency with M. polymorpha. PCR primers specific for 16S rDNA were then designed to distinguish S. medicae and S. meliloti. PCR amplification results confirmed the species allocation acquired in the glasshouse. PCR fingerprints generated from ERIC, BOXA1R and nif-directed RPO1 primers revealed that the Mediterranean strains were genetically heterogenous. Moreover PCR fingerprints with ERIC and BOX primers showed that these repetitive DNA elements were specifically distributed and conserved in S. meliloti and S. medicae, clustering the strains into two divergent groups according to their species. Linking the Sinorhizobium species with the plant species of origin we have found that S. medicae was mostly associated with medics well adapted to moderately acid soils such as M. polymorpha, M. arabica and M. murex whereas S. meliloti was predominantly isolated from plants naturally growing on alkaline or neutral pH soils such as M. littoralis and M. tornata. Moreover in glasshouse experiments the S. medicae strains were able to induce well-developed nodules on M. murex whilst S. meliloti was not infective on this species. This feature provides a very distinguishing characteristic for S. medicae. Results from the symbiotic, genotypic and cultural characterization suggest that S. meliloti and S. medicae have adapted to different Medicago species according to the niches these medics usually occupy in their natural habitats.
Recommended Citation
Garau, G., Reeve, W., Brau, L. et al. The Symbiotic Requirements of Different Medicago Spp. Suggest the Evolution of Sinorhizobium Meliloti and S. Medicae with Hosts Differentially Adapted to Soil pH. Plant Soil 276, 263–277 (2005). https://doi.org/10.1007/s11104-005-0374-0
