Dormancy in Rice Seed: III. THE INFLUENCE OF TEMPERATURE, MOISTURE, AND GASEOUS ENVIRONMENT

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Abstract
The influence of storage conditions—temperature, moisture content, oxygen, nitrogen, and carbon dioxide—on dormancy in rice seed has been investigated. The effects of temperature and oxygen when the seeds have been set to germinate have also been studied. Storage in oxygen accelerates the breaking of dormancy; at lower temperatures, the effect of oxygen is more noticeable. Carbon dioxide and nitrogen have little or no effect except in so far as they exclude oxygen. It is shown that there is a negative linear relationship between storage temperature and log. mean dormancy period of intact seeds over the range 27°C. to 47°C. In the variety tested, the Q10 for the rate of breaking dormancy is 3.38. Variation of moisture content over the range 12.0–14.5 per cent, has little effect at 27°C. and no detectable effect at higher temperatures. When dormant seeds are soaked in water, they attain a moisture content close to 30 per cent. Pre-soaking seeds to achieve moisture contents in this region can stimulate the breaking of dormancy when compared with dry storage. At laboratory temperature (mean about 27°C.) the stimulation caused by pre-soaking intact seeds is usually small and sometimes non-existent, but at a low temperature (3°C.) the stimulation is increased; but dry storage at 3°C. markedly delays the breaking of dormancy. When seeds are dehusked, a large proportion lose their dormancy. Much of the residual dormancy of dehusked seeds can be broken by soaking at laboratory temperature. But in the sample of dehusked seeds used, low temperature did not increase the effect of the pre-soaking, but slightly decreased the stimulation caused by the soaking treatment in this case. The effect of temperature on wet seed has also been investigated when the seed has been set to germinate. Maximum germination of a partially dormant population of seed is achieved at an optimum temperature which is near or somewhat below 27°C. In the sample tested, no germination occurred at 42°C., although in populations which have completely broken dormancy full germination will occur at this temperature. Non-dormant populations of rice seed can germinate at very low oxygen tensions or probably even in the absence of oxygen, but germination of a partially dormant sample is reduced under these circumstances. When oxygen tension is very low there is less germination at 27°C. than at 37°C. In some varieties, at least, there is evidence that the seeds go through a stage when they will germinate in daylight but not in the dark. A simple practical method for rapidly breaking the dormancy of intact seeds is described. The significance of these results is discussed in relation to the published work on seeds of other species.

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