The effect of leaf removal on yield and head characteristics of three varieties of oil sunflower (Helianthus annus L.)

To investigate the role of leaves at different parts of sunflower stem (Helianthus annus L.) in yield and yield components, an experiment was carried out in Amiran village, Ardestan, in 2009. Three cultivars of sunflower (i.e. Alestar, Hyson, Iroflour) were analyzed in a split-plot study following a randomized complete block design. Five levels of defoliation treatments were conducted at the beginning of pollination on the basis of R5 and the effects of five treatments (control, one-third of the upper part of stem, one-third of the middle part of stem, one-third of the lower part of stem, and complete leaf removal) were analyzed. The percent of hollow grains per head, 1000-grain weight, grain yield and biomass, harvest index, the grain oil percentage, and oil yield were evaluated. The results indicated that there was a significant difference in the varieties under study reading harvest index (at P<0.01), biomass yield, and 1000-grain weight (at P<0.05). No significant effect was observed in the percent of hollow grains, oil, and oil yield. In addition, the interaction effect of sunflower varieties and leaf removal was only significant for the percent of hollow grain per head. The oil percentage was only affected by complete leaf removal treatment. Compared to the control treatment, the complete leaf removal resulted in the highest decrease of the traits under study. From among the traits discussed above, leaf removal of the middle-part of the stem demonstrated a higher decrease in comparison to the upper- and lower-stem leaf removal.