Effect of growing degree days on autumn planted sunflower
Sunflower (Helianthus annus L.) having high degree of adaptability under wide range of climatic conditions, allow the crop to be productive in broad range of environments. Field experiments in autumn were laid out at Pir Mehr Ali Shah, Arid Agriculture University Rawalpindi, Pakistan for two years (2007 and 2008), to document the effect of growing degree days (GDD) on the performance of sunflower hybrids. Four sunflower hybrids, Alisson-RM, Parasio-24, MG-2 and S-278 were planted in randomized complete block design with four replications during autumn season. The data on growing degree days accumulation during autumn and their effect on achene, oil yield and yield components of sunflower like number of achenes per head, hundred achenes weight, biological and achene yield was recorded. All these agronomic characters as well as oil characteristics were influenced by prevailing temperature. GDD collected during autumn season was the same for both years of study. Amongst hybrids, the hybrid MG-2 showed the maximum values for all the agronomic as well as oil parameters during the autumn season. At the late planting of sunflower during autumn season, crop completes its life cycle in short duration and accumulates less heat units, thus, achene and oil yield along with yield attributes are affected accordingly.
Key words: Growing degree days (GDD), yield and yield components, sunflower.