Genetic Regulation of Development in Sorghum bicolor: III. Asynchrony of Thermoperiods with Photoperiods Promotes Floral Initiation.

Asynchronous thermo- and photoperiods were observed to hasten floral differentiation (initiation) in the short day plant Sorghum bicolor (L.) Moench. Shifting the 12 hour thermoperiod forward 0.5 or 2.5 hours hastened floral initiation compared to controls with synchronous thermo-and photoperiods. Delaying the day-night temperature change until 2.5 hours after either the dark-light or light-dark transition also hastened floral initiation. Inasmuch as sorghum milo-type maturity genotypes containing the genes designated Ma(1)Ma(2) (class I) were most responsive to asynchrony of the thermo- and photoperiods while those containing ma(3) (R) (class III) were not responsive, the maturity genes appear to control the plant's response to both photoperiod and temperature. Gibberellic acid promoted the effect of thermo- and photoperiod asynchrony on floral initiation. The results suggest that in sorghum both temperature and photoperiod may act as phase setting signals in what has previously been termed photoperiodism.