Changes in temperature sensitivity of development from sowing to flowering in rice

To accurately predict the time of flowering, it is essential to determine the effects of environmental factors on crop development at different stages. The objective of this study was to examine the variation in flowering responses to day temperature (T-D) and night temperature (T-N) during the preflowering period (PFP) in rice (Oryza sativa L.). Three controlled-environment experiments were conducted in which plants of three contrasting cultivars, CO36, Shan You 63, and Nipponbare, were transferred at different times after sowing between two constant temperatures (26 and 21 degrees C), between two T-N with the same T-D (T-D/T-N: 26/26 and 26/16 degrees C), or between two T-D with the same T-N (28/19 and 19/19 degrees C). In all experiments, the relationship between the time to flowering and the time of transfer was defined by separate]linear phases, indicating that the sensitivity of flowering responses to both T-D and T-N varies during PFP. The entire PFP can be divided into three consecutive phases. Temperature sensitivity during the second phase was greater than that during the first and third phases, which did not differ significantly. The length of the second phase varied greatly, depending on both temperature and cultivar. For all cultivars, the second phase was shorter at HT (5.4-17.0 d) than at LT (20.7 to more than 78.7 d). The duration of the first phase ranged from about 20 d in the japonica cv. Nipponbare to 32.4 to 64.2 d in the two indica cultivars. The Length of the third phase also varied among cultivars, but to a lesser extent, from 16.4 to 38.1 d. Any significant effects of temperature on main-stem Leaf number occurred in the second phase. For accurate modeling of rice flowering dates, functions describing the effects of both T-D and T-N in the second phase have to be different from those in the first and third phases.