DNA homology, phage-typing, and cross-nodulation studies of rhizobia infecting Galega species

Abstract

The taxonomic status of Rhizobium nodulating Galega sp. is poorly defined. Earlier reports suggest that the rhizobia infecting G. officinalis should be included in the R. leguminosarum species or in the "fast-growing lupin – cowpea complex." Therefore organisms nodulating G. orientalis and G. officinalis were studied using cross nodulation, DNA homology, and phage typing. No cross-nodulation relationship between the Galega rhizobia and rhizobial strains from the major taxonomic groups was found. The mean relative DNA homology of 10 strains of Rhizobium nodulating Galega with reference DNA from strain HAMBI 540, which forms effective nodules on G. orientalis, was 77 ± 9%, compared with 19 ± 6% for 20 strains from other host plants. The Galega rhizobia formed a unique phage-typing group, not related to the major groups of fast growers, in agreement with the DNA homology and cross-nodulation results. These data indicate that the Galega rhizobia form a specific taxonomic group within the genus Rhizobium.