Vergara - 1976 - Physiological and morphological adaptability of ri

194 trusarns imp RICE
Spikeiets [normal
l8 2O 22 24 26 28 2O 22 24 26 28 3O
TemperoturePCl
5. Regression curves of temperature-number of spikclcts at two stages undcr ditfcrent
sunshine hours. Model: type II l} I b,r + b_-r»" bu‘ + but‘ ~ but + c. Data for l966-H.
23 prefectures in Japan.
factors. These curves were estimated by the model type ll. which included the 4th
degree of I, using the data stratified by 2 hours of sunshine.
The above temperature curves have a clear optimum at 20°—23°C and a rise
again at 27°—28°C. This may suggest that the temperature-number of spil-aelets
curves have two tuptima. although the second optimum cannot be determined
exactly for lack of samples.
Such a temperature curve with ha optima was observed experimentally by
Tsunoda (1964). He measured the rebponse of yield components of rice plants to
water temperature constantly controlled throughout the whole growth period.
Figure 6 indicates that at the early growing stage, the only optimum for tiller
numbers was found at a high temperature of about 35°C. thereafter. with
grovt-‘th, the optimum seemed to shift to a lower temperature range. But the
disappearance of tillers became considerable in the temperature range of 25°-
30°C at IS-Ztldays before heading time. Consequently. the temperature-number
of panicles relation wah represented by the curve with who optima at 20 and
35°C. Similar results were obtained by Matsushima ct al. (l964b). Toriyama and
Tabuchi (1972) conducted phytotron experiments, using 40 varieties of indica
rice and japonica rice and observed that the number of panieles per plant was
significantly’ smaller at 25°C than at 20° and 30°C. It was also found that the
increase in number of panicles at high temperature (30%) was considerably
higher in indica rice than injaponica (Fig. 7).
The complex temperature response may be explained by an alyzing the competing
biological reactions in plants. Tsunoda (1964) observed that the number