Phenetic similarity and DNA base sequence homology of root nodule bacteria from New Zealand native legumes and Rhizobium strains from agricultural plants

Abstract A comparison was made between 65 strains of root nodule bacteria from indigenous New Zealand legumes and 45 reference strains including: Rhizobium trifolii, R. phaseoli, R. leguminosarum, R. meliloti , and both “acid‐producing” and “non‐acid‐producing” strains from the Lotus‐Lupinus‐Ornithopus cross‐inoculation group. The strains were classified into 10 clusters on the basis of 37 morphological, cultural, and physiological tests. Relationships disclosed among the reference strains were in accordance with current ideas on Rhizobium taxonomy. The indigenous strains were well separated from both the trifolii‐leguminosarumphaseoli complex and R. meliloti but acid‐producing strains from the Lotus‐Lupinus‐Ornithopus cross‐inoculation group segregated with the indigenous strains. The principal characters differentiating the clusters are discussed. The base composition of DNA from representative indigenous strains was determined and base sequence homology studied. The relative reassociation at 65°c in 0.28m phosphate buffer between DNA from R. trifolii TA1 and DNA from 3 R. lupini strains and 9 indigenous strains averaged 18%. Reassociation between DNA from acid‐producing R. lupini strains CC809a or CC811 and indigenous strains averaged 55% and 62% respectively. Reassociation between DNA from the indigenous strain NZP 5105 and other indigenous strains averaged 64%. The proportion of non‐complementary bases included in reassociated heterologous duplexes was determined from the melting profiles of the duplexes formed at 65°c. Reassociated duplexes from R. trifolii contained about 1% of non‐complementary base pairs. Reassociated duplexes of DNA from CC809, CC811, and NZP5105 with DNA from indigenous strains contained an average of 9.0, 8.5, and 5.6% of non‐complementary base pairs, respectively. Base sequence homologies did not substantiate the distinctions between primary clusters containing New Zealand indigenous rhizobia proposed by the phenetic classification, but they confirmed that indigenous rhizobia are more closely allied with acid producing R. lupini than with R. trifolii . The relationships among rhizobia are discussed in relation to those reported for the genus Agrobacterium in which the genetic composition of the population is much more clearly understood than it is for Rhizobium .