Influence of temperature and daylength on phenology on sunflowers in the field

Abstract

Phenological development of a range of sunflower (Helianthus annuus) cultivars was studied for a series of planting dates at Tamworth, New South Wales. The effects of extended photoperiod on development were also examined. As constant photoperiod was increased from 15 to 21 hours, time from sowing to first anther increased by nine to twelve days. Natural photoperiod for winter and summer planting gave times similar to that for constant 18 hour photoperiod. Days from sowing to first anther decreased substantially with later planting from June to November, but increased again for a February planting. Use of a growing degree day summation with a base of 1�C (GDD1) enabled time from sowing to first anther to be predicted with precision over a wide range of temperatures within and between years. A GDD1 summation of 1245 was found for the early cultivar, Voronezskij, and of 1380 for the mid season cultivar, Stepniak.