The effect of drought stress in various stages of sunflower growth was studied in this research with ten treatments,including:two non and well watered controls(T2,T1 respectively),treatments with severe and moderate drought stress in vegetative stage(T4,T6 respectively),treatments with severe and moderate drought stress in reproductive stage(T3,T5 respectively),treatments with stress in grain filling and floweing stages(T9,T10 respectively),irrigation along with vegetative stage and full appearance of capitulum(T8),and only one irrigation at the first of sowing,flowering and grain filling stages(T7).The resbits showed that the plants were more sensetive to drought stress during the flowering and anthesis stage,regarding capitulum diameter and 1000-grains weight.With regarding to plant height,the plants were sensetive to drought up to the full appearance of capitulum.The time of stress had no significant effect on stem diameter but this factor responded more to total amount of water.Drought stress in flowering and anthesis,increased hull percentage,and regarding the oil percentage, the grain filling stage was the sensetive period to the stress.The number of leaves decreased in treatments with drought up to flowering,but this had no effect on grain yield.The grain yield was only significantly affected by drought exerted at stage of flowering and anthesis but oil yield also was affected by drought at grain filling stage.
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