Effect of sowing date on head diameter in sunflower

Head diameter is very important trait in the sunflower seed yield structure. The size of head diameter influences the number of flowers and seeds per head which directly influence the seed yield per plant. In order to evaluate the effect of sowing date on head diameter, 3 sunflower hybrids, sown in 4 sowing dates during three growing seasons, were carried out. Head diameter was evaluated in the stage of flowering and physiological maturity. Head diameter at the stage of flowering was largely influenced by the year (Y) of investigation (46.6%), although other sources of variation (H-hybrid, SD-sowing date) showed also significance, except interaction H × SD. The largest head diameter is manifested in the hybrid Pobednik (11.9 cm) in the three-year average. In SD4 (20th of May) head diameter had the highest value (11.8 cm). In physiological maturity head diameter varied significantly depending on the sowing date (18.6%). Years, as well as hybrids had no significant influence on this trait. All interactions (Y × SD, H × SD, Y × H × SD), except year × hybrid (Y × H), were highly significant