Photoperiodic Control of Floral Initiation in Sicklepod (Cassia obtusifolia L.)

Sicklepod (Cassia obtusifolia L.) has a critical daylength of 14 h for floral initiation, and flowers when given four successive cycles of 8-h photopcriod and 16-h dark period. When 1 min of red light irradiation of adequate intensity was inserted between the sixth and ninth hours of the dark period, floral initiation was completely inhibited. When the intensity of red light was too low, the time required to inhibit floral initiation completely was too long for repromotion by subsequent far-red light irradiation. When 1 min of red light of adequate intensity for floral inhibition was immediately followed by 2 min of far-red light, floral initiation was repromoted; but when the dark period between red and far-red irradiations was too long, floral initiation was not repromoted. Sicklepod exhibited multiple reversibility of floral induction. The flowering response was time dependent and after a period was irreversible. When prolonged far-red irradiation was begun at the seventh hour of darkness, the percentage of plants flowering decreased after 2 min of irradiation and progressively decreased to about 20% after 90 min.