EFFECT OF NICKEL ON SEED GERMINABILITY OF SOME ELITE SUNFLOWER (HELIANTHUS ANNUUS L.) CULTIVARS

nutrient solution. The low concentration (10 and 20 mg L-1) of nickel significantly promoted seed germination and improved early seedling growth while higher levels (40, 20 and 60 mg L-1) caused a significant inhibition in germination and resulted in a considerable delay to achieve 50 % germination. Although, plumule and radicle length, and fresh and dry weights of germinating seeds were also improved at lower concentrations, they were significantly reduced in all cultivars at higher levels of nickel. Magnesium (Mg) contents in plumule and radicle also increased at lower levels of nickel but they were significantly reduced at higher Ni levels. However, plumule and radicle K contents consistently reduced with increasing concentration of Ni in the growth medium. The maximum nickel tolerance level in all cultivars appeared to be 40 mg L-1 at which all parameters were reduced more than 50%. Overall, cv. Hysun-33 was more tolerant whereas, Nust-160 the sensitive. All other cultivars were intermediate in nickel tolerance at the germination stage