Phenotypic, Genotypic and Symbiotic Characterization of Rhizobial Isolates Nodulating Acacia sp. in Morocco

Thirty eight isolates nodulating acacia were isolated from different Moroccan areas to determine their ability to survive under various stress conditions, in order to select resistant ones. The response of these isolates to different environmental stress was evaluated to show their preliminary variability based on phenotypical characteristics. Tolerance to increasing levels of NaCl (0.5-10% w/v), pH (4.8-11), temperature (4-55°C) and resistance response to seven heavy metals and five antibiotics were studied as phenotypic markers. The majority of isolates from different Acacia trees were fast growing. Numerical analysis of these phenotypic characteristics showed that the isolates were divided into three distinct clusters presenting intra and intercluster diversity. The symbiotic effectiveness of different isolates was studied and showed significant differences with respect to nodule number, nitrogen fixation and improving plants growth (shoot and root dry weight) compared to the uninoculated and non-fertilized control under greenhouse conditions. On the basis of phenotypic and symbiotic studies, six isolates (I1, I3, I5, I6, I16 and I28) were selected for genotypic characterization. The selection of such rhizobial isolates able to adapt to various environmental stress conditions and to improve plant’s growth is important for their future valorization to develop inoculants for Acacia especially in arid areas.