Genetic diversity of indigenous Rhizobium leguminosarum bv. viciae isolates nodulating two different host plants during soil restoration with alfalfa

A total of 360 Rhizobium leguminosarum bv. viciae strains was isolated from three brown-coal mining restoration fields of different age and plant cove r (without and in the first and second year of alfalfa, Medicago sativa, cu ltivation) using two host species (Vicia hirsuta and Pisum sativum) as capt ure plants. The strains were genetically typed by restriction fragment leng th polymorphism analysis of polymerase chain reaction (PCR)-generated 16S-2 3S ribosomal DNA intergenic spacer regions (IGS-RFLP) and characterized by plasmid profiles and RFLP analysis of amplified nodABC genes. The R. legumi nosarum bv. viciae population was dominated by the same group of strains (i rrespective of the trap plant used). According to type richness, the geneti c diversity of indigenous R. leguminosarum in the second year of restoratio n was lower than in the first year and it resembled that of the fallow fiel d, except for plasmid types, in which it was higher than that of the fallow field. Some of the less frequent nodABC genotypes were associated with dis tinct chromosomal IGS genotypes and symbiotic plasmids (pSyms) of different sizes, indicating that horizontal transfer and rearrangements of pSym can occur in natural environments. However, the dominant pSym and chromosomal g enotypes were strictly correlated suggesting a genetically stable persisten ce of the prevailing R. leguminosarum bv, viciae genotypes in the absence o f its host plant.