Relationship between transpiration and ripening of rice grain

The relationship between transpiration from spikelet and increase of grain dry-matter for diverse rice cultivars was examined. The transpiration rate per surface area of spikelet at 10 hPa of vapor-pressure-deficit reduced gradually after ear emergence in the tested cultivars. For cultivars which showed high mean values of transpiration rate between 5 and 10 days after heading, dry matter increase of the grain was higher than that for low transpiration rate cultivars. There was a significant positive correlation between the transpiration rate and relative growth rate of grain during the ripening period in almost all cultivars. A saturation deficit of atmosphere lower than 7 hPa and higher than 13 hPa during the ripening period reduced 1,000-grain weight in most cultivars. Prevention of grain transpiration by plastering with vaseline after flowering significantly obstructed ripening of the grain. Transpiration from rice grains, therefore, suggested a relation with their ripening, while the optimum transpiration rate for increasing grain dry-matter might vary among cultivars.