GERMINATION BEHAVIOR OF ACACIA TORTILIS (FORSSK.) HAYNE VAR RADDIANA (SAVI) BRENAN AND A. NILOTICA VA (L.) WILLD. EX DELILE VAR ADSTRINGENS (SCHUMACH. ET THONN.) ROBERTY SEEDS FROM THE HOGGAR, ALGERIAN SAHARA UNDER OSMOTIC, THERMAL AND SALT STRESS

Abstract

Seeds of Acacia tortilis var raddiana and A. nilotica var adstringens harvested from the Hoggar (Algerian Sahara) were tested for germination under 3 abiotic constraints usually present in their biotope, i.e. thermal, salt and osmotic stress. Results showed a different behavior of the two species. Germination speed is better for A. tortilis in all situations. Germination rate under tested temperatures was similar for both species except 15°C which revealed obviously unfavorable on A. nilotica germination which dropped from a high of 96.6% at 40°C to a low of 11% at 15°C while that of A. tortilis slightly decreased from 92% at 40°C to 80% at 15°C. Regarding germination behavior under salt stress, A. tortilis maintained 21% of germination under a salt concentration of 350mM while seeds of A. nilotica did not germinate at concentrations above 150 mM suggesting a better tolerance of the former species to salt stress. The same trend applies also in the case osmotic stress with A. tortilis maintaining a germination rate of 26.7% at a PEG-6000 concentration of 240g/l while A. nilotica showed a germination rate of 21% at a much lower PEG-6000 concentration, i.e. 40g/l. These results indicate a greater adaptive capacity of A. tortilis in the face of environmental constraints and may partially explain its wider distribution in the Algerian Sahara. These results contribute to a better understanding of the germination behavior of these two species in a perspective of their in situ and/or ex situ propagation.