Direct-seeding method on dry paddy soil could make rice farming large-scale cultivation and cost-saving, but it has still some problems on poor seedling establishment caused by low temperature and varying sowing depth. This research was carried out to identify weedy rice genetic resources that may help to poor seedling establishment in direct-seeded rice on dry paddy soil in temperate region. The genetic resources screened in this study were 128 accessions that consist of 92 japonica weedy rices, 24 indica weedy rices, and 12 Korean bred cultivars.The weedy rices on average have very superior abilities to emerge form depth than cultivated rice. The germplasm showed that the coleoptile or/and mesocotyl lengths were positively correlated with emergence rate to a high degree. Among the germplasm, WD-3, a japonica weedy rice, evidenced the highest level of emergence with the longest coleoptile and mesocotyl elongation. The emergence ability of WD-3 depending on the burial depth under low temperature condition was confirmed in both the phytotron and the field conditions. WD-3 showed 100% of emergence rate until a burial deptho f 7 cm in the dry soil in the phytotron, and 76.2 % of very high emergence rate in the total layer of paddy field where the seeds were sown from the surface to 10 cm depth. In the emerged plants in the field, the mesocotyl elongation increased with increasing burial depth in a logarithmic fashion, and the coleoptile extension increased exponentially. The total elongation lengths of the mesocotyl and coleoptile were similar with a plant burial depth, which indicated that they could induce the safe emergence of the main leaf of the seedling from the soil to thesurface. Conclusively, the elongation habit of mesocotyl and coleoptile of WD-3 could be one of the important characteristics to develop direct-seeding cultivars.

The elongation of mesocotyl and coleoptile plays important roles in the seedling emergence and stand establishment of dry direct-seeded rice. Experiments were carried out to elucidate the effects of seed-presoaking treatments of GA3 and some inorganic salts on the mesocotyl, and coleoptile elongation of rice. Seed-soaked GA3 promoted the elongation of mesocotyl, but little effect on the coleoptile elongation. The stimulation effects of GA3 were found to be enhanced by addition of CaCl2 However, the sole treatment of CaCl2 showed no stimulating effect on the mesocotyl and coleoptile elongation. Mesocotyl elongation was most prominent in the combined treatments of 50ppm GA3 with 100 mM CaCl2 . The synergistic effects of GA3 and CaCl2 on mesocotyl elongation varied with varietal groups. The stimulating effects of GA3 were enhanced significantly by the addition of CaCl2 in japonica varieties, Dongjinbyeo, Ilpumbyeo and Milyang 95, and tall indica variety, Labelle, but not in semidwarf Tongil type varieties, Tongilbyeo, Milyang 23, and Nampungbyeo, and semi-dwarf indica, Short Labelle. The promoting effects of GA3 on the mesocotyl elongation were decreased in proportion to the lowered osmotic potential by PEG 6000 on the contrary to CaCl2 This implies that the synergistic effects of CaCl2 with GA3 on mesocotyl elongation was not caused by osmotic potential lowered by CaCl2 addition but by the salt itself. Salts such as Ca(NO3 )2 , MgCl2 BaCl2 , NaCl, KCl and KNO3 showed the synergistic effects with GA3 on mesocotyl elongation as well. The degree of synergistic effects showed no differences among salts tested, implying that there is no specificity of ions constituting the salts.

보리 4품종, 밀 4품종, 호밀 3품종, 옥수수 1품종을 가지고 파종 심도를 달리 하였을 때 이들 작물들의 초엽장과 식물체장을 조사하였고 또 이들 간의 상관을 조사한 결과를 요약하면 다음과 같다. 1. 보리, 밀, 호밀, 옥수수가 발아할 때 생기는 관 아래의 절간을 중경 또는 지하경 이라고 호칭하고 있는데 지하경으로 부르는 것이 옳을 것 같으며 보리, 밀, 호밀은 초엽이 종자로부터 지하경과 함께 나오고 옥수수는 지하경 정단의 관에서 나오는 것을 확실하게 해두는 것이 좋을 것 같다. 2. 보리의 초엽의 길이는 파종 심도가 깊어질수록 현저하게 길어지고 식물체장도 같은 경향이 있는데 보리의 2cm파종은 6cm, 10cm깊이 파종 보다 현저하게 짧게 나타났다. 품종간에는 차이를 볼 수 없었다. 3. 밀의 초엽 길이도 마찬가지로 파종 심도에 따라 현저하게 길어졌으며 2cm 파종은 6cm, 10cm 파종보다 현저하게 짧게 나타났으나 보리보다는 못하였다. 이것도 품종간 차이는 별로 나타나지 않았다. 4. 호밀과 옥수수도 파종 심도가 깊어질수록 초엽이 길어졌으며 그 변이가 보리와 밀보다 크게 나타났다. 호밀과 옥수수에서 변이가 컸다. 5. 각 작물과 품종들에 있어서 초엽과 식물체장 간에 유의성이 있는 상관을 보였고 칠보 호밀은 고도의 유의성을 나타내었다.