Diversity of rhizobia isolated from Tunisian arid soils capable of forming nitrogen-fixing symbiosis with Anthyllis henoniana

Abstract

Soils in arid and infra-arid regions of Tunisia (where rainfall does not exceed 180 mm) suffer from rapid degradation of vegetation cover and loss of biodiversity. To limit the progress of desertification, it is necessary to promote the cultivation of autochthonous plants and particularly legumes, pioneer plants used for the restoration of poor soils. 50 strains were isolated from soils of five locations throughout arid areas in Tunisia using Anthyllis henoniana, a woody Saharan legume. 16S rRNA gene sequencing and multilocus phylogenetic analysis using recA and dnaK genes grouped rhizobial isolates into six clades, three of them related to the genus Rhizobium (36%), particularly R. leguminosarum, R. sullae and R. radiobacter, two related to Ensifer (56%), E. meliloti and E. numidicus, and one related to Neorhizobium (8%). Twelve selected strains were assayed for symbiotic efficiency using A. henoniana. Strains related to Ensifer and R. sullae were symbiotically efficient; demonstrating for the first time that they are natural symbionts of A. henoniana in Tunisian arid soils. Strains Ensifer sp. AZ2.5 and Rhizobium sp. AE4.7 were the most efficient in nitrogen fixation, suggesting that these strains could be interesting inoculants to enhance A. henoniana adaptation and growth in poorly vegetated regions.