The Role of Leaf Area and Head Size on Sunflower Yield Physiology in Different Conditions of Water Availability

Abstract

This study was aimed at investigating the effect of source and sink manipulation on the yield of a sunflower hybrid in different water availability conditions. The experiment was conducted as a split plot in 2015 in Gonabad, Iran. Irrigation regimes during the reproductive stage at two levels, including optimal irrigation (ETP 100%) and water stress (ETP 50%), were assigned to main plots. Manipulating of the source and sink, including removing 50% of all leaves at the bottom, removing 50% of all leaves at the top of the stem, removal of 50% of head seeds, removal of 25% of head seeds, and control treatment (No removal of leaves and seeds) were assigned to the subplots. A 25 % reduction in head size in favorable irrigation conditions did not reduce the yield compared to the control, but other treatments caused a decrease in grain yield, the highest amount of decrease in grain yield was seen in the treatment of halving the head by 62.2%. In the condition of water stress, none of the defoliation treatments caused a reduction in grain yield, but the removal treatments of 25 and 50 percent of the head caused a significant decrease in grain yield by 40.1 and 79.3 percent, respectively. These results show that in optimal irrigation conditions, the strength of the source, both at the top, and bottom of the canopy, is the limiting factor of the yield. However, in the condition of water stress, severe sink capacity limitation occurred.