Increasing soil salinity represents a major constraint for agriculture in arid and semi-arid lands, where mineral nitrogen (N) deficiency is also a frequent characteristic of soils. Biological N fixation by legumes may constitute a sustainable alternative to chemical fertilisation in salinity-affected areas, provided that adapted cultivars and inoculants are available. Here, the performance of three peanut cultivars nodulated with two different rhizobial strains that differ in their salt tolerance was evaluated under moderately saline water irrigation and compared with that of N-fertilised plants. Shoot weight was used as an indicator of yield. Under non-saline conditions, higher yields were obtained using N fertilisation rather than inoculation for all the varieties tested. However, under salt stress, the yield of inoculated plants became comparable to that of N-fertilised plants, with minor differences depending on the peanut cultivar and rhizobial strain. Our results indicate that N fixation might represent an economical, competitive and environmentally friendly choice with respect to mineral N fertilisation for peanut cultivation under moderate saline conditions.

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The phenotypic and genotypic characterization of sixty-two rhizobial isolates obtained from nodules of Arachis hypogaea in north-western Morocco was performed. Their physiological and biochemical properties revealed a great deal of diversity among them. Isolates were classified into two major groups based on the numerical analysis of their phenotypic and genotypic characteristics. Isolates in the first group were alkali- and salt-sensitive, slow or extra-slow growers; they did not use disaccharides as carbon source and varied in the use of amino acids. ARDRA analysis of the 16S rDNA region grouped them together with reference strains belonging to the genus Bradyrhizobium. In the second group, isolates were fast growers, acid-sensitive, and alkali- and salt-tolerant; they used both mono and disaccharides as carbon sources, and methionine was the only amino acid they could metabolize as a nitrogen source. ARDRA analysis grouped them with fast-growing reference strains. Both groups exhibited a range of variability in tolerance to heavy metals. The Intergenic Spacer (IGS)-PCR fingerprinting analysis confirmed a high genotypic diversity at the strain level. This characterization provides a basis for the selection of peanut-nodulating rhizobia which may have applications in formulating appropriate inocula for improving peanut crop yield on Moroccan soils, including saline and acidic marginal areas.

Seventy bacterial strains were isolated from root nodules of the legume Hedysarum flexuosum grown wild in soils from Northwest Morocco. Repetitive extragenic palindromic (REP)-polymerase chain reaction (PCR) clustered the strains into 30 REP-PCR groups. The nearly complete sequence of the 16S rRNA gene from a representative strain of each REP-PCR pattern showed that 17 strains were closely related to members of the genus Rhizobium of the family Rhizobiaceae of the Alphaproteobacteria. Pairwise alignments between globally aligned sequences of the 16S rRNA gene indicated that the strains from H. flexuosum had 99.75-100% identity with Rhizobium sullae type strain IS123(T). The phenotypic characteristics analyzed allowed description of a wide physiological diversity among the isolates, where the carbohydrate assimilation test was the most discriminating. Analysis of the 16S rRNA gene of a representative strains from the remaining 13 REP-PCR groups showed they belong to a wide variety of phylogenetic groups being closely related to species of genera Stenotrophomonas, Serratia, Massilia, Acinetobacter, Achromobacter, and Pseudomonas from the Beta- and Gammaproteobacteria. The R. sullae strains identified in this study produced effective symbiosis with their original host plant. None of the other bacterial strains could form nodules on H. flexuosum.

Nitrogen stress as well as other stresses can negatively impact the plant development and metabolism. Generally, stress factors increase the reactive oxygen species (ROS) and methylglyoxal (MG) production, which may, in the absence of effective protective mechanisms, induce irreparable metabolic dysfunction and death. The effect of different amounts (from deficiency to excess) of nitrate, ammonium or nitrate combined to ammonium, on enzyme activities of antioxidant and methylglyoxal detoxification systems of two sorghum ecotypes (3P4 and 4P11) was studied. The N supply was performed per pot during the sowing step using potassium nitrate and/or ammonium sulfate. Six N treatments were applied using 120, 240 and 480 Kg ha-1 of ammonium or nitrate and three other treatments were applied using 120 kg ha-1 nitrate combined to 120, 240 and 480 kg ha-1 of ammonium. The specific activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione reductase (GR), glyoxalase I (Gly I) and glyoxalase II (Gly II) were investigated. Results showed that, ammonium excess and N-deficient conditions increased the contents of malondialdehyde (MDA), and induced the enzyme activities of ROS and MG detoxification systems, supporting the sorghum's ability to counteract the negative effect of N stress (deficit and excess). We have also shown that the SOD, CAT, GR and Gly I enzyme activities were higher in the 4P11 ecotype compared to the 3P4 ecotype. These results indicate that sorghum ecotypes exhibit differential tolerance to N stress and suggest that the 4P11 ecotype has higher capacity to cope with N stress.