Etude de la germination des graines d'Acacia tortilis sous différentes contraintes abiotiques

Study of Acacia tortilis seed germination under different abiotic constraints. Since Tunisian acacia populations are threatened by regression, we analyzed as a preliminary study the germination behavior of the species in order to plan subsequently for a preservation and rehabilitation program. In this context and to optimize acacia seed germination and to overcome and remove the obstacle of tegumentary inhibition, we have in a first attempt tested several physical (scarification, boiled water) and chemical (sulfuric acid) pretreatments under different temperatures. Thus, we could determine the optimal germination conditions that have been used afterwards for evaluating the germination capacity of the species under different osmotic constraints. Several concentrations of NaCl (0 to 22 g.l-1) and PEG (0 to -8 bars) were applied on seeds. Parameters related to germination capacity and kinetic were assessed and analyzed. Thus, soaking seeds in concentrated sulfuric acid for one hour allowed us to improve the germination rate and its speed. When studying the effect of the temperature on the germination process, we showed that 25°C could improve the rate and average time of germination. Under osmotic stress, we found a highly significant treatment effect (PEG concentrations) on the germination rate and average time of germination, and the species did not display a high drought tolerance behavior (since germination is totally inhibited under -8 bars). Moreover, the study of the effect of salt stress on germination revealed a highly significant effect of NaCl concentrations on the germination rate and average time of germination, and a good level of salt tolerance since it succeeded to germinate under high salt concentrations (21% of germination rate under 22 g.l-1NaCl). In conclusion, our study clearly showed that germination capacity of Acacia tortilis under the environmental constraints and factors is sufficiently assured to consider this species for a reforestation program and to extend consequently its area of distribution.