A Study of Thermal Requirements of Developmental Stages of Sunflower in Kaboutarabad of Isfahan

For studying thermal requirements of developmental stages of sunflower based on number of days and accumulated growing degree days (GDD) and relationship of these stages with vegetative growth and seed and oil yield, fourteen hybrids and one open pollinate sunflower genotypes were chosen and evaluated by using a randomized complete block design in four replications in 2005 at the kabotarabad Agricultural Research station of Isfahan. The Number of days and cumulative growing degree days (GDD) from planting to staring, blooming, flowering, 75 percent flowering, 100 percent flowering and physiological maturity were highly and significantly affected by genotypes. Genotypes clustering, based on 14 developmental stage trait showed the sunflower genotypes grouping in early, mid and late maturity groups. Open pollinate cultivar was placed in mid ripening group. The correlation coefficients among vegetative and reproductive growth with number of days and growing degree days of developmental stages were generally positive and significant. According to the results, physiological maturity period and related cumulative growing degree days are the most effective period on seed yield. Oil percentage had not any significant correlation with developmental stages and accumulated growing degree days.