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 (T-D) and night temperatures (T-N) on plant developmen t. The objective of this study is to determine whether there are diffe rent effects of T-D and T-N on development from sowing to flowering in rice (Oryza sativa L.). Plants of 24 cultivars were grown in naturall y-lighted growth chambers at five diurnally constant (22, 24, 26, 28 a nd 32 degrees C) and four diurnally fluctuating temperatures (26/22, 3 0/22, 22/26 and 22/30 degrees C for T-D/T-N with 12 h d(-1) each) with a constant photoperiod of 12 h d(-1). The treatments were selected to enable the separation of effects of T-D and T-N on development rate ( DR). The response of DR to constant temperatures was typically nonline ar. This nonlinearity could not explain the difference in flowering da tes between fluctuating temperatures with the same mean daily value bu t opposite T-D/T-N differences. Differential effects of T-D and T-N on DR to flowering were detected in all but one cultivar. In most cases, T-D exerted a greater influence than T-N, in contrast with many previ ous reports based on the assumption of a linearity between DR and temp erature. The data were further analysed by a nonlinear model which sep arated effects of T-D and T-N. The estimated value for the T-N was gen erally 25-29 degrees C, about 2-4 degrees C lower than the estimated o ptimum T-D in most cultivars. The effects of T-D and T-N on DR were fo und to be interactive in some cultivars. These results form a new basi s for modelling flowering dates in rice. (C) 1996 Annals of Botany Com pany