Abstract

As a major problem in many rice-producing areas, grain chalkiness influences milling percentage, cooking and eating quality. In this study, we investigated the influences of different temperature regimes, e.g. (1) low (25/20°C), (2) high (35/28°C) and (3) natural condition on chalkiness, head rice rate and other related physiological and biochemical characteristics of early indica rice at grain filling stage. The results showed that the lowest chalkiness was 22.59% under low temperature treatment and the highest chalkiness was 61.11% under high temperature treatment. The highest head rice rate was 62.33% under low temperature treatment followed by 49.91% in the control and the lowest was 42.76% under high temperature treatment. Higher amylose content in rice grain was found under the low temperature treatment. The net photosynthesis rate (NPn) and chlorophyll content in flag leaves reduced significantly under both low and high temperature treatments than the control, i.e. lower photoassimilates produced under both high and low temperature treatments in comparison with the control. Although NPn was different among the treatments, the lowest chalkiness was observed under low temperature treatment. Malondialdehyde, proline and soluble sugar content in flag leaf were also influenced by high and low temperature stress. Scanning electron microscopic of rice kernels showed that the chalky kernels contained loosely packed and globular shaped starch granules with many air spaces than nonchalky kernels.