Caractérisation Des Propriétés D’adaptation Anatomiques Et Physiologiques, Au Milieu Saharien De Vachellia Tortilis (forssk.) Galasso & Banfi Subsp. Raddiana (savi) Kyal. & Boatwr. (cas De Méguiden

Résumé: This work aimed to establish an anatomical and physiological properties and drought tolerance of Vachellia raddiana called formerly Acacia raddiana, which is a taxon with raised stately belonging to Fabaceae family, that allowed it to progress and to reproduce in the algerian Sahara; environment known for its severe edaphic and climatic conditions. To achieve this end, we have approached 3 aspects: The first, a stress simulation by induction of PEG to allow the physiological traits of acclimatization to express, applied on Vachellia raddiana seedlings aged of eight weeks, achieving 3 levels of potential (0, -0.25 et -0.5 MPascal). The second aspect, consisted of applying four concentrations of aqueous extracts of Vachellia raddiana adult (2; 1; 0.5; and 0.25%), on the seeds of Retama raetam and calculate their germination indices. Finally, the third was devoted to study of the rate and duration of Vachellia raddiana’s seeds germination under the effect of pretreatment. The results obtained indicated that the species Vachellia raddiana is characterized by an osmotic adjustment capacity face of water stress by showing a tolerance towards the desiccation. In fact, the stomas declined their openings from 16.89 ± 2.55 μm face of stress, the weakest being at 4.21 ± 0.4 μm after application of extreme stress. According to our test, the seedling has an anatomical "tolerance" in the stoma, which was maintained during the first 24 hours after induction of stress S2 (Ψ h at -0.25 bar), corresponding to a tolerance vis-à-vis to this level. Similarly for extreme stress Ψ h at -0.5 bar, where the plant exhibited a low Cortex /Diameter ratio of the stem biometrics throughout the experiment, which caused by water withdrawal and dehydration of cell wall, influencing their size. Regarding the impact of the tree on the underlying flora, our results revealed that by applying the soil extract at 0.5% we obtained a rate of 13 ± 1.48%. It is the same for the pure extract of the whole plant of Vachellia raddiana, with a content of 146.26 mg Equi. AG / g MS in polyphenols, which showed some efficiency on seed germination of Retama raetam with 12 ± 1.49% germinated seeds. Concerning the delay of germination, 50% of the totality of the applied treatments (physical, chemical and combined) showed a time similar to the positive control namely 3 days. Regarding the third aspect, our results showed that the combined treatment between sand and Capsicum frutescens L. solution diluted at 25%, presented the best rate which is 100%, where the complementarity between the abrasive action of the sand and the exothermic action of the Capsicum solution, expressed a positive additive effect on the germination rate. However, the germination time was only improved by the 25% diluted Capsicum solution. In support to the abovementioned, concerning the adaptation characteristics of the taxon in the saharan environment, and according to our results, the interaction of these parameters allowed the plant to a better adaptation to a crucial element in the saharan area, namely dehydration, during the juvenile, adult and latent phases of its life cycle.

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