Thermotolerance and Osmotic Potential Studies in Germinating Seeds and Growing Seedlings of Acacia sieberiana and Acacia tortilis

The effects of temperature and osmotic potential on germination and radicle elongation of Acacia sieberiana and Acacia tortilis ssp. heteracantha seeds were studied. The first series of experiments examined percentage germination under continuous temperature treatments of 15, 25, 27, 30 and 35°C in distilled water and / or PEG 6000 solutions adjusted to –0.1;-0.2 and –0.5 MPa. The thermal optimum for germination and radicle elongation for both species was found to be between 25 and 30°C. Both species showed progressive reduction in germination rates and radicle elongation in response to decreasing osmotic potential. A. tortilis was found to germinate under the widest range of temperature and osmotic potentials. A. tortilis also exhibited higher percent germination than A. sieberiana, but A. sieberiana showed greater radicle growth when compared with radicle elongation displaced by A. tortilis