Abstract
The short-day response of rice plants has been considered to be promotion of heading by reducing the period of deletable growth phase (DGP) which is the period from turning point of leaf emergence to panicle initiation. The present research suggested the existence of photoperiodic sensitivity in not only DGP but also the reproductive phase (RP) which has been regarded as non-photoperiodically sensitive. We evaluated the photoperiodic sensitivity at DGP, RP and the basic vegetative growth phase (BVP) which is the period from germination to turning point of leaf emergence. As a result, all three growth phases were sensitive to photoperiod and the duration of each phase was reduced by a short day length. Especially, the photoperiodic sensitivity showed a larger varietal difference in DGP than in the other phases. There was a positive correlation between the days to heading and photoperiodic sensitivity in DGP and RP. These results showed that DGP was sensitive to photoperiod and played an important role in deciding earliness of variety. Although no relation was observed with earliness, photoperiodic sensitivity in BVP was lager in Japonica varieties than in Indica varieties. Analysis of the experimental results, according to the growth phase classification used in present study, revealed that each growth phases showed photoperiodic sensitivity and that the sensitivity changed with growth phase transition unlike the conventional theory. Therefore, by using the present method, the photoperiodic sensitivity can be studied in more detail.
