Effects Of Salinity, Alkalinity, Drought And Temperature On Seed Germination Of Sunflower (Helianthus Annuus L.)

Sunflower (Helianthus annuus L.) belonging to the family Asteraceae is the world's fourth largest oil-seed crop. And it is also one of the most important oil seed crops in China. Environmental abiotic stress conditions, such as light,salinity, drought and temperature, are currently the major factors that reduce crop yields worldwide. Among them however, salt and drought is the main factor which limits seed germination and seedling establishment of plants growing in saline soil of arid and semi-arid regions. Salinity can affect germination of seeds either by creating osmotic potentials that prevent water uptake or by toxic effects of specific ions. The aim of this work was to evaluate the germination of Helianthus annuus L. seeds under increasing salinity by using the most abundant salts in west Jilin province in China in eleven types of salts and polyethyleneglycol, in order to determine the difference between three cultivars and the factors that inhibiting seed germination. Treatments for all solutions were 0, 100, 200, 300, 400, 500mM and PEG was at the same water potential with NaCl solution at three alternating temperature regimes of 10-20, 15-25 and 20-30oC in a 12h dark/ light photoperiod. The cations content (K⁺, Na⁺ and Ca²⁺) in hypocotyls were determined on the 5th day. Effects of salinity, temperature and their interactions on final percentage and the rate of germination were evaluated.The study indicated that seed germinated best in control, and the percentage of germination decreased as salinity increased. Among the three cultivars, SDM is the most tolerant to salt and PEG stress. Different cultivars sunflower germinate best in different temperature, and germination was inhibited once the temperature was higher or lower than this value. Both NaCl and PEG inhibited germination, but the effects of NaCl compared to PEG were less, which means that adverse effects of PEG on germination were due to osmotic effect rather than specific ion accumulation. At same concentration of salt solution, the adverse effect of ions is in the following sequence: CO₃^2- > SO₄^2- , HCO₃^- >Cl^-, Mg²⁺> Ca²⁺ and Na⁺ > K⁺. The effect of salinity on the germination phase of development is mainly due to its osmotic component other than the ion toxicity.