Symbiotic status and strains of rhizobia linked to Acacia tortillis subsp raddiana [Acacia raddiana s. s.] mimosoidea of the desert regions of Algeria

Acacia tortilis (Forsskal) Hayne subsp. raddiana (Savi) Brenan [Acacia raddiana Savi s.s.] is the most widely spread woody legume in desert regions of Algeria. As a well-adapted species, it represents a good potential for forestation or reforestation in these areas. Its capacity to establish a nitrogen-fixing symbiosis with rhizobia constitutes an important characteristic for its development and its adaptation to such environmental conditions. For these reasons, the authors have conducted a study on the prevalence of the symbiosis in this species and on the characterization of their associated rhizobial strains. The evaluation of 101 plants from nine natural sites and eight nurseries revealed that nitrogen-fixing nodules are generally present in A. tortilis subsp. raddiana, despite the harsh edaphic conditions prevailing in natural and nursery environments of southern Algeria. Symbiotic characterization of 51 strains of rhizobia associated with A. tortilis subsp. raddiana allowed to demonstrate that these are not very specific and can, for most of them, form nitrogen-fixing nodules in other acacias species of Algerian desert areas, namely Acacia seyal Del. and Acacia ehrenbergiana Hayne. Therefore, these strains have a potential for inoculum production for inoculation of A. tortilis subsp. raddiana as well as other species of acacias. Analysis of restriction patterns of RNA 16S genes of these rhizobia strains allowed to demonstrate their wide diversity. They were essentially represented by species of the genus Ensifer, mainly Ensifer meliloti, and less so by species of Mesorhizobium and Rhizobium genera, as already documented by several authors in other parts of Africa. In addition to the rhizobia species already recognized as associate of A. tortilis subsp. raddiana, the authors have isolated five strains that could not be identified, using polymerase chain reaction - restriction fragment length polymorphism of RNA 16S gene, and that might represent a new genotypic species.