Prediction of flowering in sunflowers

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Abstract
Models based on growing degree day summations (GDD) for the prediction of 50% flowering (50F) were developed using phenological data obtained from monthly plantings of the open pollinated sunflower [Helianthus annuus] cv. Sunfola 68-2 and the hybrid Hysun-30 at Biloela [Queensland, Australia] over the period Sept. 1974-Aug. 1975. These models were tested on independent data obtained from plantings made in 1973-1976. The base temperatures for the computation of GDD were -1.3.degree. C for Sunfola 68-2 and -5.9.degree. C for Hysun-30. Day length affected phenology and leaf number during the emergence to head visible stage (E-HV). The data suggested that Sunfola 68-2 was either day-neutral or had a short day response, and Hysun-30 a long day photoperiod requirement. These differences led to the development of different models for the prediction of 50F. The model for Sunfola 68-2 used GDD with no adjustment for day length, but day length adjustment was necessary for Hysun-30. Reliable predictions of 50F for Biloela were given by the equations: Sunfola 68-2: GDD (E-50F) = 1351.7 .+-. 51.8 (base -1.3.degree. C) Hysun-30: GDD (E-50F) = (2835.0 - 133.1 DL) + 668.2 .+-. 23.9 (base-5.9.degree. C) where DL = (day length at planting + day length 1 mo. later)/2.