CHARACTERIZATION OF AN INDIGENOUS POPULATION OF RHIZOBIA NODULATING LOTUS-CORNICULATUS

This report describes some immunological, biochemical, genetic and symbiotic properties of 15 isolates of rhizobia nodulating Lotus corniculatus from representative Uruguayan soils. Based on specific growth rates, carbon source utilization and acid production the isolates could be assigned to the fast-growing group of rhizobia. The analysis of the electrophoretic cell protein profiles of each of the 15 isolates were unique, suggesting that they represent different strains of rhizobia. Ten of the 15 isolates belonged to a same serogroup as indicated by their cross-reactivity with antisera raised against R. loti strain B816. The analysis of plasmid content showed that out of 13 isolates examined 6 contained a single megaplasmid of about 300 Mda and 3 harboured a plasmid of 130 Mda in addition to a megaplasmid. One isolate harboured two megaplasmids and no plasmids could be detected in three other isolates. No hybridization to any of the identified plasmids was detected when R. meliloti nif D DNA was used as nif probe. However, strong hybridization signals were observed with restricted total DNA, suggesting a chromosomal location of nif genes in these isolates. Plant growth experiments carried out under bacteriological controlled conditions revealed that all these isolates effectively nodulate L. corniculatus and their symbiotic effectiveness were similar or higher than the commercial inoculant strain (B816).