Biodiversity of rhizobia associated with sainfoin (Onobrychis viciifolia) in South Africa

Abstract

Sainfoin (Onobrychis viciifolia) is a perennial crop with multiple agricultural and environmental benefits, as well as biotechnological applications. When used as forage, it can remedy the problem of bloating in livestock through condensed tannin production. Studies have shown that O.viciifolia extracts also display anti-inflammatory and antimicrobial activity, showing the potentialof application in the pharmaceutical industry. Although resistant to drought, O. viciifolia is oftenprone to nitrogen deficiency. This problem can be mitigated by the symbiotic relationship thatexists between the roots and rhizobia. These bacteria inhabit the root and facilitate nitrogenuptake by the plant through nitrogen fixation. Little information is known regarding the biodiversityof rhizobia nodulating the O. viciifolia root. This study was therefore conducted to isolate andcharacterise these bacterial species. Unbroken nodules were selected from the roots of threedifferent O. viciifolia cultivars, one endemic (Esparsette) and two exotics (Perly and Taja). Thesenodules were then prepared aseptically and their bacteroids cultivated for molecular identificationand phylogenetic analysis. DNA extraction and polymerase chain reaction (PCR) amplificationmethods were used prior to identification via the NCBI database using the BLASTn tools. Theresults revealed that in addition to rhizobial microorganisms that inhabit the O. viciifolia rootnodules there were non-rhizobial microorganisms as well. The bacterial composition variedaccording to cultivar. The endemic cultivar, Esparsette, grown during this study in a greenhouse,comprised of rhizobial microorganisms from the genera Rhizobium, while the Esparsette obtainedfrom a farm in Ficksburg comprised of Mesorhizobium. The exotic cultivars comprised of rhizobialmicroorganisms from the genera Rhizobium. The diversity of non-rhizobial microorganisms fromthe three cultivars included Agrobacterium, Bacillus, Curtbobacterium, Enterobacter,Paenibacillus, Peribacillus, Pseudomonas, Pseudoxanthomonas, Spirosoma and Xanthomonas.These identified isolates were screened in vitro for direct plant growth-promoting traits thatincluded phosphate solubilisation, siderophore production, Indole acetic acid (IAA) production andnitrogen fixation. The rhizobial isolates from all the cultivars showed positive results for phosphatesolubilisation and nitrogen fixation and varied results for the non-rhizobial isolates. Varied resultsfor siderophore production and IAA production were observed for both the rhizobial and non-rhizobial isolates. It can be concluded that the bacterial population found within the nodules ofdifferent sainfoin cultivars comprises a diverse group of symbiotic as well as non-symbioticmicroorganisms that are functionally diverse.