Abdelkader Bekki

Symbiotic characterization and diversity of rhizobia associated with native and introduced acacias in arid and semi-arid regions in Algeria.

The diversity of rhizobia associated with introduced and native Acacia species in Algeria was investigated from soil samples collected across seven districts distributed in arid and semi-arid zones. The in vitro tolerances of rhizobial strains to NaCl and high temperature in pure culture varied greatly regardless of their geographical and host plant origins but were not correlated with the corresponding edaphoclimatic characteristics of the sampling sites, as clearly demonstrated by principal component analysis. Based on 16S rRNA gene sequence comparisons, the 48 new strains isolated were ranked into 10 phylogenetic groups representing five bacterial genera, namely, Ensifer, Mesorhizobium, Rhizobium, Bradyrhizobium, and Ochrobactrum. Acacia saligna, an introduced species, appeared as the most promiscuous host because it was efficiently nodulated with the widest diversity of rhizobia taxa including both fast-growing ones, Rhizobium, Ensifer, and Mesorhizobium, and slow-growing Bradyrhizobium. The five other Acacia species studied were associated with fast-growing bacterial taxa exclusively. No difference in efficiency was found between bacterial taxa isolated from a given Acacia species. The tolerances of strains to salinity and temperature remains to be tested in symbiosis with their host plants to select the most adapted Acacia sp.-LNB taxa associations for further revegetation programs.

Impact of single and co-inoculations with Rhizobial and PGPR isolates on chickpea (Cicer arietinum) in cereal-growing zone soil

ABSTRACT Strains isolated from chickpea (Cicer arietinum L.) rhizospheric soil from selected sites in Algeria were screened for their plant-growth-promoting potential, for indole acetic acid production and P solubilization ability. Then, we selected native rhizobial strains with high nitrogen-fixing potential. On the basis of their efficiency under controlled conditions, two plant-growth-promoting rhizobacteria (PGPR) isolates and three nodulating bacteria were selected. Then, the effect of single PGPR isolates inoculation was compared to their combination with rhizobial inoculants on plant growth, on native cereal-growing soils under greenhouse conditions. No effects were observed on chickpea yield by using rhizobial inoculation alone, nor by PGPR-rhizobial co-inoculation on two soils presenting weak and no nodulation pattern in natural conditions. Only PGPR inoculation improved growth of plants on soil with no nodulation pattern. These findings emphasized inoculation on native soils at a little scale before large assays on field because no one could predict inocula behavior with native soil microflora.

Diversity of nodular bacteria of Scorpiurus muricatus in western Algeria and their impact on plant growth

A total of 51 bacterial strains were isolated from root nodules of Scorpiurus muricatus sampled from 6 regions of western Algeria. Strain diversity was assessed by rep-PCR amplification fingerprinting, which grouped the isolates into 28 different clusters. Partial nucleotide sequencing of the 16S rRNA gene and BLAST analysis revealed that root nodules of S. muricatus were colonized by different species close to Rhizobium vignae, Rhizobium radiobacter, Rhizobium leguminosarum, Phyllobacterium ifriqiyense, Phyllobacterium endophyticum, Starkeya sp., and Pseudomonas sp. However, none of these strains was able to form nodules on its host plant; even nodC was present in a single strain (SMT8a). The inoculation test showed a great improvement in the growth of inoculated plants compared with noninoculated control plants. A significant amount of indole acetic acid was produced by some strains, but only 2 strains could solubilize phosphate. In this report we described for the first time the diversity of bacteria isolated from root nodules of S. muricatus growing in different regions in western Algeria and demonstrated their potential use in promoting plant growth.