Defoliation effects on yield and yield components of sunflower cultivars (Helianthus annuus L.)

An experiment was conducted on two early maturing cultivars of sunflower, Megasal and Haysun36, to evaluate the effects of different defoliation treatments on yield and yield components. The experiment took place at the educational-research farm of the Miyaneh branch of Islamic Azad University, in the growing season of 2008. The design of the experiment was factorial, based on randomized complete block design with 3 replications. Shrub morphologic and physiologic characteristics were studied to evaluate shrub dry weight, chlorophyll content, leaf area index (LAI), harvesting index (HI) and oil yield. The results demonstrated that the defoliation treatments had significant difference on yield components and the other studied traits. The results also demonstrated that statistical comparisons of the cultivars indicated no significant difference among the studied traits other than those results for head diameter, chlorophyll content, LAI, HI, weight of 1000 grain, unfilled seed percentage, seed and oil yield. In this experiment, interaction between different defoliation treatments and the cultivars for studied traits (other than head diameter, chlorophyll contents, HI, seed number in head and, the weight of 1000 grain) were no significant.