Effect of foliar application of ascorbic acid (vitamin c) and irrigation withholding in different growth stages on quantitative and qualitative characteristics and some biochemical's changes in Sunflower (Helianthus annuus L.)

In order to study the effects of water deficit stress and foliar application of ascorbic acid, an experiment was conducted in research field of Islamic Azad University, Varamin Branch in Iran during 2012 growing season. The experimental design was laid out in a randomized complete block design with a split plots arrangement in three replications. Main plots included four different levels of irrigation (complete irrigation, irrigation withholding at 8-leaf stage, irrigation withholding at grain filling stage and irrigation withholding at both 8-leaf and grain filling stages) and three different concentration of Ascorbic Acid foliar application (0, 100 and 200 ppm) was allocated to subplots. The results showed that irrigation withholding conditions in different growth stages significantly decreased seed yield, biological yield, harvest index, oil and protein percentage, oil and protein yield and total chlorophyll content but by contrast increased proline content and superoxide dismutase activity in leaves. Foliar application of ascorbic acid as antioxidant enzyme could increased quantitative and qualitative yield and chlorophyll content and decreased proline and superoxide dismutase activity in leaves by reduction of water deficit stress. Foliar application of Ascorbic Acid with 200 ppm under irrigation withholding at both 8-leaf and grain filling stages increased 38/46% yield seed compared with treatment that foliar application without Ascorbic Acid. In addition, Ascorbic Acid foliar application reduced the harmful effects of water deficit stress as antioxidant and improved growth conditions for water deficit stress.