The Effect of Temperature on Leaf Appearance in Rice

Temperature is the principal environmental determinant of crop leaf appearance. The objective of this study is to analyse whether there are different effects of day temperature ( TD ) and night temperature ( TN ) on main-stem leaf appearance in rice ( Oryza sativa L.). Plants of 12 rice cultivars were grown at five constant temperatures (22, 24, 26, 28 and 32 °C) and four diurnally fluctuating temperatures ( TD / TN : 26 /22, 30 /22, 22 /26 and 22 /30 °C) with a constant photoperiod of 12hd -1 . The leaf appearance on the main stem was measured. A constant change in leaf appearance rate was observed during ontogeny. The relation between the number of emerged leaves and days from seedling emergence was described by a power-law equation with only one cultivar-specific parameter. Values for this parameter were estimated for the five constant temperature treatments, and the relation between this parameter and temperature was quantified by a nonlinear model. Leaf appearance for the four fluctuating temperature treatments could be accurately predicted on the basis of these relations in each cultivar. This indicated that there were no specific effects of TD and TN on leaf appearance in rice, in contrast with phenological development to flowering. The optimum temperature for leaf development was found to be substantially higher than for development to flowering. The final main-stem leaf number differed with diurnal temperature conditions. When a diurnal temperature delayed flowering, it increased the leaf number as well. This might explain why TD and TN had a different effect on development to flowering but not on leaf development.