Abstract
A simple equipment that rises the panicle temperature of rice in the daytime was developed to screen the strains of rice that were tolerant to high temperatures during the ripening stage. High temperature stress at the ripening stage is the main cause of chalky grains and hence degrades the grain quality. Fitting a clear plastic film tube made with OHP film (3M, PP2500) around the panicle increased the spikelet temperature by around 0.8°C without any effect on leaf photosynthesis. Attaching a black rubber sponge with a 2cm width and 5mm thickness inside the tube further rised the temperature by more than 2°C. The higher the spikelet temperature, the higher was the percentages of chalky grains. Although a slight lowering of night temperature (about 0.15°C) by setting this equipment was observed, its effect on the occurrence of chalky grains seemed to be negligible. Evaluation of standard cultivars with different high temperature ripening tolerance indicated that the result of evaluation by this method well matched that by other evaluation methods. This method makes it possible to evaluate high temperature tolerance with only a single plant, which consequently makes it possible to evaluate the tolerance of segregating populations, although progeny testing might be necessary. Accordingly, it might be useful for the genetic analysis of the high temperature tolerance.
