ارزیابی تغییرات صفات مهم زراعی و معیارهای سنجش تحمل به خشکی در ارقام آفتابگردان

Two field experiments were conducted in 1996 at the experimental station, College of Agriculture, Shiraz University at Badjgah. Fourteen cultivars consisting of eight hybrids and six open pollinated cultivars were grown in two randomized complete block designs with four replications. The well-watered experiment received water when evaporation reached 65±5 mm from class A evaporation pan. The water-limited experiment was irrigated in terms of 125±5mm evaporation from class A evaporation pan. Days to flowering, days to physiological maturity, head diameter, stem diameter, number of leaves per plant, plant height, number of filled seeds per head, 1000 seed weight, kernel percentage, unfilled seed percentage, seed yield, oil percentage, oil yield and harvest index were measured. Most of the traits including seed yield and oil yield showed considerable genotypic and phenotypic variations. Highly significant differences were observed among cultivars. In normal and water stress conditions, the highest seed yield were obtained by Louc and Armavirsky cultivars, respectively. Water stress significantly decreased yield and its components. Furthermore, days to physiological maturity reduced in response to water deficit. However, oil percentage did not differ significantly. Drought resistance indexes were calculated in order to evaluate the response of each cultivar to water deficit. No association was found between yield potential and the stress susceptibility index, suggesting that drought resistance and high yield potential may be combined to improve sunflower cultivars. In addition, it was revealed that selection for height mean productivity and stress tolerance index will improve yield and drought tolerance simultaneously. Among cultivars that were used in this study, Armavirsky, besides having a relatively higher yield, was also drought tolerant.