Effects of Light, Temperature and Osmotic Stress on Seed Germination of Eucalyptus occidentalis Endl

Abstract

Seed germination of E. occidentalis was examined under different combinations of light, temperature and osmotic potential. The effects of all three factors were found to be interrelated. Germination rates are directly related to the temperature of the environment between 15 and 30�C and to the osmotic potentials of the medium between -9.1 and 0 bars. The relative require- ment for light, i.e. the ratio of light germination to dark germination, increases with the rise in temperature. Light is a decisive factor in improving germination under osmotic stress; its effect is directly related to the intensity of stress. In media with an osmotic potential of -9.1 bars, the effect of light on germination is directly related to temperature. Optimum germination occurs at 30" under continuous light and under no osmotic styes. Very low germination is obtained under the same temperature in the absence of light and in a medium with an osmotic potential of -9.1 bars. Inhibition of germination caused by osmotic stress is 2-3 times as great as that caused by dark stress. Seed germination was found to vary according to an annual rhythm. Lower rates of germination were obtained in July and January, whereas maximum germination occurred from March to May.