The present study deals with the effect of caffeine on callus initiation and growth from hypocotyl explants of Helianthus annuus, Explants exhibits response for callus initiation when caffeine added to MS medium (MS+0.5 mg/L NAA +1.0mg/L BA ). The best was that with 0.5 mg/L caffeine in which the fresh weight of callus reached 5.176g after 35 days of culture . It was Also found that addition of caffeine to MS medium alone with 1.0 mg/L BA enhanced initiation and growth of callus the highest fresh weight was 3.920g obtained when 5.0 mg/L caffeine added with 1.0 mg/L BA .
It was also found that with addition 1.0 mg/L 2,4-D to MS medium containing 0.5 mg/L caffeine callus growth was better than its growth when 2,4-D alone was added, so the fresh weight of callus reached 1.150 g . It was noticed that addition of 0.5 mg/L NAA to MS medium containing different concentrations of caffeine led to initiation of callus, and the callus differentiation of roots specially when 0.5 mg/L was added with 2.5 mg/L caffeine 87.5% root formation was obtained .
The results cleared that addition of caffeine alone with different concentrations to MS medium enhanced root formation. The best medium was that MS with addition of 2.5 mg/L caffeine which enhance 11 roots with 12.6 cm in length that after 35 days .