Legume-nodulating bacteria (LNB) from three pasture legumes (Vicia sativa, Trigonella maritima and Hedysarum spinosissimum) in Tunisia

Genetic diversity of rhizobia isolated from nodules of Trigonella foenum-graecum L. (fenugreek) cultivated in Northwestern Morocco

The present work aimed to characterize rhizobia nodulating Trigonella foenum-graecum L. (fenugreek) cultivated in six different geographical locations in Northwestern Morocco. Forty-seven rhizobial isolates from nodules of Trigonella foenum-graecum were grouped into thirteen clusters using the Rep-PCR technique. The phylogenetic analysis based on 16S rRNA gene sequences of 13 groups showed that all representative strains were closely related to members of the genus Ensifer (syn. Sinorhizobium) of the Alphaproteobacteria. All the representative strains shared 100% similarity with Ensifer medicae WSM419^T. NodC and nifH gene analysis revealed a close phylogenetic relationship of the representative strains with those of the strains belonging to the symbiovar meliloti. Furthermore, nodulation ability of our rhizobial strains was efficient in their host plant (Trigonella foenum-graecum L.).

Spore associated bacteria regulates maize root K+/Na+ ion homeostasis to promote salinity tolerance during arbuscular mycorrhizal symbiosis

BACKGROUND

The interaction between arbuscular mycorrhizal fungi (AMF) and AMF spore associated bacteria (SAB) were previously found to improve mycorrhizal symbiotic efficiency under saline stress, however, the information about the molecular basis of this interaction remain unknown. Therefore, the present study aimed to investigate the response of maize plants to co-inoculation of AMF and SAB under salinity stress.

RESULTS

The co-inoculation of AMF and SAB significantly improved plant dry weight, nutrient content of shoot and root tissues under 25 or 50 mM NaCl. Importantly, co-inoculation significantly reduced the accumulation of proline in shoots and Na+ in roots. Co-inoculated maize plants also exhibited high K+/Na+ ratios in roots at 25 mM NaCl concentration. Mycorrhizal colonization significantly positively altered the expression of ZmAKT2, ZmSOS1, and ZmSKOR genes, to maintain K+ and Na+ ion homeostasis. Confocal laser scanning microscope (CLSM) view showed that SAB were able to move and localize into inter- and intracellular spaces of maize roots and were closely associated with the spore outer hyaline layer.

CONCLUSION

These new findings indicate that co-inoculation of AMF and SAB effectively alleviates the detrimental effects of salinity through regulation of SOS pathway gene expression and K+/Na+ homeostasis to improve maize plant growth.

Characterization of Rhizobial Bacteria Nodulating Astragalus corrugatus and Hippocrepis areolata in Tunisian Arid Soils

Fifty seven bacterial isolates from root nodules of two spontaneous legumes (Astragalus corrugatus and Hippocrepis areolata) growing in the arid areas of Tunisia were characterized by phenotypic features, 16S rDNA PCR-RFLP and 16S rRNA gene sequencing. Phenotypically, our results indicate that A. corrugatus and H. areolata isolates showed heterogenic responses to the different phenotypic features. All isolates were acid producers, fast growers and all of them used different compounds as sole carbon and nitrogen source. The majority of isolate grew at pHs between 6 and 9, at temperatures up to 40°C and tolerated 3% NaCl concentrations. Phylogenetically, the new isolates were affiliated to four genera Sinorhizobium, Rhizobium, Mesorhizobium and Agrobacterium. About 73% of the isolates were species within the genera Sinorhizobium and Rhizobium. The isolates which failed to nodulate their host plants of origin were associated to Agrobacterium genus (three isolates).