The relationships between planting dates and yield and it's components in sunflower was evaluated through orthogonal polynomial regression analysis. Five field experiments were conducted during the summer season of 2011 to study the effect of five planting dates and three oilseed sunflower genotypes and their interactions on yield and yield components of sunflower. The highest seed yield, oil yield, plant height, head diameter, 1000-seed weight, seed yield plant-1 and oil content were obtained at the earliest planting date (1st May). The evaluated genotypes differed significantly for all the studied traits. Sakha 53 cultivar was the best cultivar in seed yield, oil yield, plant height, head diameter, thousand seed weight and seed yield plant plant-1 followed by Giza 102 and Pioneer hybrid 63M02, respectively. Orthogonal polynomial regression analysis revealed that, yield and yield components were significantly affected by planting date in linear responses. Multiple linear regression analysis indicated that seed yield plant-1, head diameter and thousand seed weight were the most important variables contributing toward higher seed yield (kg ha-1). Finally, it can be concluded that planting sunflower cultivar Sakha 53 on 1st May was recommended for maximizing seed and oil yields per unit area under the environmental conditions of this study.
Key words: Sunflower, planting date, genotype, regression analysis, yield, yield components.
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