Effect of Different Levels of Salinity and Drought Stress on Seed Germination Characteristics and Seedling Growth of Forage Turnip (Brassica rapa L.)

Salinity and drought stress are among the common environmental factors which adversely affect germination and growth of plants. This experiment was conducted to evaluate the effects of salinity and drought stress on turnip seed germination and early growth in seed lab of College of Agriculture, University of Tehran, during 2010. The experimental design was a complete randomized block with three replications. The salinity and drought treatments were applied by sodium chloride and PEG, respectively, to create five levels of osmotic potentials of control (zero), -3, -6, -9 and -12 bars. The measured properties were germination percentage, radical, shoot and seedling length, seedling dry weight, mean time to germination, germination rate and seedling vigor. The results indicated that both salinity and drought stress, adversely affected all the measured parameters in turnip. As the severity of salinity and drought stress increased, the percentage and rate of germination followed a linear decreasing trend. However, in terms of drought stress by increasing the osmotic potential to -3 bar, the length of radical, shoot and seedling as well as seedling dry weight significantly increased compared to control while in stress levels over than -3 bars all these properties followed a decreasing trend. As the severity of salinity stress increased, the growth of seedling followed a linear decreasing trend. In the most severe stress level (-12 bars), for both salinity and drought stress, no radical or shoot were formed. The results of this experiment indicated that turnip is a sensitive crop to salinity and drought stresses at early stages of growth. It was also concluded that the salinity stress is more effective on turnip germination and development compared to drought stress.