ABSTRACT

The effects of highly effective strains of Sinorhizobium meliloti on biomass and crude protein yields of alfalfa (Medicago sativa L.) were investigated in a three-year field experiment focusing on the advantage of alfalfa inoculation with N microbiological fertilizer over N mineral fertilization on chernozem soil. Strains 236 and 234 were found in this experiment to have significant effect on the yields of dry matter and proteins, by comparison to untreated control plants. In the third year of utilization, dry matter yield of alfalfa plants inoculated with strains 236 and 234 increased around 31% in the first cutting and 53% and 65% in the second one, compared to control plants. Strain 236 was found to increase the yield of crude proteins by 29.7% (second cutting) and 39.6% (third cutting) in the second year, and 27.5% (first cutting) and 50.3% (second cutting) in the third year of utilization, while strain 234 increased significantly the content of proteins in the third cutting of the second year (27%) and in the third year of utilization (51% in the first and 53% in the second cutting). The results indicate that effective strains of S. meliloti may be applied as N microbiological fertilizers on soils with optimal physical and chemical characteristics and autochthonous populations that may not have satisfactory effectiveness in nitrogen fixation.

No abstract

We have evaluated the genetic diversity and phylogeny of alfalfa rhizobia, originating from different types of soils in Serbia and their ability to establish an effective symbiosis with alfalfa (Medicago sativa L.). A collection of 65 strains isolated from root nodules of alfalfa were characterized by rep-PCR analysis, partial and complete 16S rDNA gene and recA gene sequencing, as well as atpD gene sequencing and DNA-DNA hybridizations. The results of the sequence analyses revealed that Sinorhizobium meliloti is the dominant species in alfalfa nodules. Only one strain was identified as Sinorhizobium medicae, two strains as Rhizobium tibeticum and one strain as Rhizobium sp. Despite the fact that the majority of strains were identified as S. meliloti, a high genetic diversity at strain level was detected. Almost all isolates shared the ability to nodulate and fix nitrogen with M. sativa, except 11 of them, which were incapable of fixing nitrogen with this species. About 50% of the isolates showed values of symbiotic effectiveness (SE) above 50%, while 10% of the strains were highly effective with SE values above 70%. Some of the strains which were highly effective in nitrogen fixation at the same time could intensively solubilize phosphates, offering a possibility for multipurpose inoculum development. This was the first genetic study of rhizobia isolated from this region and also the first report of natural presence of R. tibeticum in root nodules of M. sativa

Rhizobium leguminosarum bv. trifolii is microsymbiont Trifolium pratense and Trifolium repens, which are very important legumes in Serbia. The natural nodulating population of those bacteria was collected and estimated biodiversity distribution by monitoring dominant genotypes of these bacteria. The population of Rhizobium leguminosarum bv. trifolii were collected from 50 marked locations of 11 types of soil in Serbia. 437 natural isolates, rescued from nodules of Trifolium repens or Trifolium pratense, were analyzed by phenotypic approach. We obtained 156 different isolates on the basis of differences in their IAR - intrinsic antibiotic resistance (five antibiotics) and HMT- heavy methal tolerance (five heavy metals). We investigated 56 dominant isolates with more than three differences in IAR-HMT patterns by REP-PCR and RAPD fingerprinting (AP10 and SPH 1 primers). The results showed genodiversity of dominant Rhizobium leguminosarum bv. trifolii field isolates and offered the possibility to assess their changes on marked locations during time and under different environmental conditions and geographical distribution