Physiolgical and Ecological Studies on Barnyard Grass (Echinocloa crus-galli Beauv. var. oryzicola Ohwi) : I. On the primary dormancy of the seed. (1) Relation of the seed covering to dormancy, and effects of temperature and oxygen on breaking dormancy.

Abstract

Fundamental studies in eradication of barnyard grass (Echinocloa crus-galli Beauv. var. oryzicola Ohwi), an annoying weed in rice cultivation, have been done by the authors with physiological and ecological techniques. The present report deals with the primary dormancy in the seed, and the results of experiment are as follows; 1. It was elucidated that the primary dormancy was due to the presence of the pericarp and epidermis and not of the shell coat (Fig. 1). It was also suggested that the delayed germintaion of the dormant seed might not be associated with impermeability of the seed coat to water. 2. A high temperature treatment (40°C∼50°C) was found effective in overcoming the dormancy, and a wet condition at 5°C was also effective in accelerating the process of after-ripening, though it was ineffective at 20°and 30°C. Both non-and deep-dormant seeds showed no response to the alternated temperature. But the dormancy of partially dormant seeds were overcome by the treatment, the effectiveness being attributed to the low temperature as well as alternation of temperature (Fig. 2). Freezing treatment (-5°C) was effective in overcoming dormancy only in partially dormant seeds (Fig. 3). 3. In order to judge the effect of the storage at various temperatures in overcoming dormancy, both the freezing treatment and the storage treatment in submerged soils were carried out with the seeds that were considered to have been processed to a certain degree of dormancy through air-dry storage. The storage at 5°C promoted overcoming of dormancy, but storage at the optimum temperature for germination lead the seeds back to deeper dormancy (Fig. 4). 4. The storage in nitrogen gas (without oxygen gas) acclerated awakening of the seed from dormancy, and this acceleration was more remarkable in the partially dormant seeds, and awakening was faster at 30°C storage condition than at 5°C condition (Table 1).