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Models based on growing degree day summations (G.D.D.) for the prediction of 50 per cent flowering (50F) were developed using phenological data obtained from monthly plantings of the open pollinated sunflower cultivar, Sunfola 68-2, and the hybrid, Hysun-30, at Biloela over the period September 1974 to August 1975. These models were tested on independent data obtained from plantings made from 1973 to 1976. The base temperatures for the computation of G.D.D. were found to be -1.3�_C for Sunfola 68-2 and -5.9�_C for Hysun-30. Daylength affected both 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 G.D.D. with no adjustment for daylength, but daylength adjustment was necessary for Hysun-30. Reliable predictions of 50F for Biloela were given by the equations : Sunfola 68-2 : G.D.D. (E-50F) = I351.7 �_ 51.8 (base -1.3�_C) Hysun-30: G.D.D. (E-50F) = (2835.0-133.1 DL)+668.2 �_ 23.9 (base -5.9�_C) where DL = (Daylength at planting + Daylength one month later)/2 |
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