Variability of head diameter in sunflower hybrids depending on planting date

Head size contributes substantially to seed yield of sunflower because it influences both number of seeds per head, and seed size. The aim of this field study was to determine the variability of head diameter in sunflower hybrids depending on planting date across three cropping seasons. Three hybrids (Miro, Rimi, Pobednik) were sown at four planting dates (PD1 - 20th of March, PD2 - 10th of April, PD3 - 30th of April, PD4 - 20th of May). Head diameter was analysed in the stage of flowering and physiological maturity. The trial was arranged as Randomized Complete Block Design (RCBD) with four replications. Analysis of variance (ANOVA) showed that the effect of year, hybrid, planting date and most interactions were highly significant for head diameter in the flowering stage. In the stage of physiological maturity head diameter varied significantly depending only on the planting date. Also, all interactions, except year × hybrid (Y × H), were highly significant. Planting date had significant influence on head diameter in the stage of flowering and physiological maturity in sunflower. With later sowing head diameter increased, so that significantly highest head diameter across planting dates was found in PD4 (11.8 cm in flowering stage, and 22.6 cm at the stage of physiological maturity). Study results may be helpful in the recommendation for optimal planting date in sunflower.