Ecological Studies on Alopecurus aequalis Sobol., a Noxious Weed in Winter Cropping. : 9. On the secondary dormancy of the seed.

Abstract

The seeds which have awaked from the primary dormancy are then exposed to the secondary dormancy under certain conditions. The following facts were found concerning the secondary dormancy. 1. The seeds which have been kept within submerged soil outdoors become to show poor percentage germination since November, and hardly germinate in a germinator at 20°C in February of the next year, that is to say the secondary dromancy is induced. The secondary dormancy is overcome by August and induced again in November. And this process is repeated till the seeds lose their viability (Fig. 1). 2. With progress of the secondary dormancy under submerged soil, maximum and optimum temperature for germination become lower together with poor percentage germination (Fig. 2). 3. The secondary dormancy is induced experimentally by placing the seeds showing the environmental dormancy under absence of oxygen at low temperature 5°C, and to a certain extent at 20°C, but not induced at 30°C (Fig. 3, 4). 4. The secondary dormancy is overcome by low-temperature treatment (Fig. 5), high-temperature treatment in normal air or in absence of oxygen (Fig. 6), alternating-temperature treatment (Tab. 1) and pricking seeds coats (Fig. 7), as observed with the primary dormancy. And the low-temperature treatment and alternating-temperature treatment are effective similary to overcome the second secondary dormancy (Fig. 8). 5. Accordingly, it was well established that the seeds in the soil, if no germination occurs because of unfavorable condition for germination (such as in lower layer of the soil in poor-drained fields), are forced to go into the secondary dormancy under the condition of oxygen absence at low temperature in winter, and the dormancy is overcome under the condition of oxygen absence at higher temperature in summer. The mechanism of overcoming the secondary dormancy was seemed to be similar to the primary dormancy.