Genetic diversity of rhizobia associated with alfalfa in Serbian soils

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

Production of indolic compounds by rhizobial bacteria

“…Comparing the detected concentrations of IAA in Bradyrhizobium and Ensifer strains indicates a clearly lower production in representatives of the genus Bradyrhizobium. These results are in agreement with the findings of Stajković-Srbinović et al, (2012;2020), which showed a weaker production of auxin by Bradyrhizobium spp. strains compared to Sinorhizobium spp.. B. japonicum strains are known to synthesize IAA, both as free-living forms in soil and as bacteroids in soybean nodules (Hunter, 1987;Minamisawa and Fukai, 1991).…”

“…Most of the strains belonging to Ensifer meliloti species (Stajković-Srbinović et al, 2012) reached the highest detectable level of IAA of 200 µg ml -1 (designated as ≥200 µg ml -1 ), while the lowest detected concentration was 15 µg ml -1 . The strains producing 15 µg ml -1 of IAA belong to Rhizobium tibeticum species, whereby visual observation IAA production could not be detected (color change).…”

Live soil inocula, not host population or domestication status, is the predominant driver of growth benefits to cowpea

“…Prior to that, it had been an alfalfa field for 4 years. Like cowpea, alfalfa is a legume; however, it generally associates with Ensifer, and does not form nodules with Bradyrhizobium (Stajković-Srbinović et al 2012;Wang et al 2018;Woliy et al 2019). Bioinoculants such as the one used at Shafter are employed to prime soils without a history of successful prior production of a particular legume, making this site a perfect candidate for inoculation.…”

Rhizobium inoculants for alfalfa in acid soils: A proposal for Uruguay

“…However, Ramírez-Bahena and others (34) showed that under controlled conditions, inoculation of alfalfa with selected acid-tolerant strain improved plant biomass production. In Serbia, where the use of commercial inoculants for alfalfa is not a common practice (52) , Stajkoviae-Srbinoviae and others (47) found that in soils with pH between 5.1 and 8.1 most of the nodules of M. sativa were occupied by E. meliloti. Additionally, Deliae and others (52) identified effective native alfalfa strains in acid soils, which represented an interesting finding because 50% of Serbia's arable soils are acid.…”