Differential Effects of Day and Night Temperature on Development to Flowering in Rice

There are conflicting reports with regard to difference in effects of day temperature ( TD ) and night temperatures ( TN ) on plant development. The objective of this study is to determine whether there are different effects of TD and TN on development from sowing to flowering in rice ( Oryza sativa L.). Plants of 24 rice cultivars were grown in naturally-lighted growth chambers at five diurnally constant (22, 24, 26, 28 and 32 °C) and four diurnally fluctuating temperatures (26 /22, 30 /22, 22 /26 and 22 /30 °C for TD / TN with 12hd -1 each) with a constant photoperiod of 12hd -1 . The treatments were selected to enable the separation of effects of TD and TN on development rate (DR). The response of DR to constant temperatures was typically nonlinear. This nonlinearity could not explain the difference in flowering dates between fluctuating temperatures with the same mean daily value but opposite TD / TN differences. Differential effects of TD and TN on DR to flowering were detected in all but one cultivar. In most cases, TD exerted a greater influence than TN , in contrast with many previous reports based on the assumption of a linearity between DR and temperature. The data were further analysed by a nonlinear model which separated effects of TD and TN . The estimated value for the optimum TN was generally 25 –29 °C, about 2 –4 °C lower than the estimated optimum TD in most cultivars. The effects of TD and TN on DR were found to be interactive in some cultivars. These results form a new basis for modelling flowering dates in rice.