What is a response to photoperiod?
Photoperiod influences the time of flowering by its effect on final leaf number. Photoperiod sensitivity commences at the emergence of the first leaf. The duration of the inductive phase can continue until terminal spikelet formation. Until then, the final number of leaves could be changed by an abrupt transition from long to short days or vice versa. Hence, the last leaf primordia and the first few spikelets primordia are labile until committed. The first sign of commitment of a primordium to be a spikelet is when a double ridge forms. The first double ridge form at about the center of the primordial stack and the process of double ridge formation proceeds upwards and downwards from that point. Double ridge may occur when 20 to 80% of spikelet primordia have been formed. However the movement of wave means that the lowest (oldest) spikelet primordium may not become committed until very late (Brooking et al., 1995). Fig. 9 Cultivars differ in their response to daylength as well as in th
