Dormancy of paddy seeds in relation to different moisture contents of grains and dates of harvests

Summary

Two dormant varieties of rice were harvested three times at intervals of 7 days after grain development and the seeds were subjected to different sunning and controlled humidity storage treatments. Germination percentages and moisture contents of the grains were recorded at intervals of seven days after harvest.

It was noted that the dormancy of the dormant rice seeds was broken early when the seeds were subjected to continuous sunning from sunrise to sunset, followed by the treatment where the seeds were preserved under 0 % humidity conditions at room temperature. There was no break of dormancy of rice seeds when the seeds were preserved under 94 % humidity conditions.

It was further noted that when the age of the seeds at the time of a germination test remained the same, the earlier the harvest, the earlier was the break of dormancy; and when the lapse of time after harvest remained the same at the time of a germination test, the later the harvest, the better was the germination.

It is suggested that dryness of the seeds helps in the early break of dormancy and wetness retards or completely stops the dormancy-breaking reactions. On drying, the kernels of rice seeds shrink in volume more than the glume covers resulting in an air-space between the glumes and the kernels. This air-space helps air-diffusion in and out of the seeds, resulting in quicker oxidation-reaction processes or possibly embryo respiration, and consequently the dormancy is broken early. Increase in temperature accelerates such reactions. It is further suggested that the dormancy of rice seeds depends on the interactions between the ‘embryo-sensitivity to inhibitors’ and the ‘state of oxidation-reaction processes’ inside the seeds.