Physiological and Ecological Studies on Barnyard Grass (Echinocloa crus-galli Beauv. var. oryzicola Ohwi) : III. On the secondary dormancy of the seed

Abstract

The following facts were found concerning the secondary dormancy of the seeds. The seeds which had been kept within submerged soil became to show poor percentage germination since August, and hardly germinated in a germinator at 30°C at the time between from September to December, that is to say the secondary dormancy was induced. The secondary dormancy was overcome at the next spring. And it was observed that this process was repeated during over four years. The activity of dehydrogenase in the embryo of secondary dormant seeds was similar to non-dormant seeds, as observed with primary dormant seeds. It was elucidated that the secondary dormancy was not caused by embryo dormancy, but was due to the presence of the pericarp and epidermis. The secondary dormancy was induced experimentally by placing the seeds showing the environmental dormancy under submerged soils at germination temperature (20 to 30°C). And, it was induced more rapidly in the seeds staying in the environmental dormancy for a longer period, and at 30°C than at 20°C, and not related with Eh value of the soil. The secondary dormancy was overcome under the conditions similar to the primary dormancy. However, it was differed from the primary dormancy in the facts that the secondary dormancy was awakened more rapidly in the upland condition than in the submerged conditon at low temperature (3 to 5°C), and the freezing treatment (-5°C) was not effective in overcoming the secondary dormancy.