This study is to identify the physiological traits of submergence-tolerant varieties of rice plants (Oryza sativa L.) in Yeongnam area, southeastern part of Korea, where the reduction of rice yield due to submergence is remarkably severe. In the present study, two tolerant varieties of rice plants were selected from over 30 rice varieties grown in under a 10-day period. The tolerant varieties selected from a submerged paddy field. As a control, one intolerant variety of rice plant was chosen. Of the tolerant variety Samgangbyeo, rather than Haepyungbyeo, had a lower dissolved oxygen consumption and maintained a higher dry weight than the intolerant variety. The leaf photosynthetic rates (LPS) of the two tolerant varieties were significantly higher than that of the intolerant-variety after four days of submergence treatment. These results indicate that lower dissolved oxygen consumption in a limited pool is prevented by ethylene formation in the tolerant varieties, which may be a mechanism of submergence tolerance.

The performance of 7 sugary (su) and 12 shrunken-2 (sh2) sweet com hybrids which are commercially grown in the United States was tested in Korea. The 100-seed weight of su hybrids (16.5-23.6 g) was much heavier compared to that of sh2 hybrids (10.9-17.5 g). The germination rate of su and sh2 hybrids at 25~circC ranged 93.3-100% and 86.7-98.9%, the emergence rate of su and sh2 hybrids in cold test ranged 78.9-97.8% and 62.2-97.8%, and field emergence rate of su and sh2 hybrids ranged 74.4-100.0% and 79.9-98.2%, respectively. In su hybrids, there was a significantly positive correlation between germination rate at 25~circC and emergence rate in cold test or early growth. In contrast, in sh2 hybrids seed weight was positively correlated with early plant growth, while not with the germination rate at 25~circC or emergence rate in cold test and field. Most sh2 hybrids produced larger and more marketable ears compared to su hybrids although there were significant differences among the hybrids in the same genotype. At harvest (24 days after pollination) soluble solids content of su hybrids (24.3-27.1 Brix %) was much higher than that of sh2 hybrids (13.8-18.0 Brix %), while total sugars of sh2 hybrids (21.4-28.6% on the dry weight basis) was much higher compared to su hybrids (2.4-15.9%). Considering germination and emergence rates, marketable ear production, and total sugar content, 'GCB 70' and 'Sweet Satin' in su hybrids and 'Ice Queen', 'Aspen', 'Sweet Magic', 'Bandit', 'Xtrasweet 82', 'Aspen', and 'Cambella 90' in sh2 hybrids performed better than other hybrids.

The studies on physico-chemical factors and phytoplankton at the 3 rivers in the Taejon city were conducted from November 1997 to May 1998. The Results were as follows; In the water quality, the down streams were generally worse than the upper streams. Water temperature was varied from 2.4℃ to 23.0℃; DO from 1.80㎎/ℓ to 17.6㎎/ℓ ; pH from 4.7 to 10.4 ; BOD from 0.78㎎/ℓ to 8.80㎎/ℓ; COD from 0.32㎎/ℓ to 8.26㎎/ℓ ; SS from 2.0㎎/ℓ to 43.0㎎/ℓ ; total phosphate was from 0.001㎎/ℓ to 0.709㎎/ℓ ; total nitrogen 0.01㎎/ℓto 11.69㎎/ℓ . In phytoplankton species, they were identified as total 191 taxa composed of 8 classes, 18 orders, 35 families, 74 genera, 152 species, 35 varieties and 4 forms. The dominant species were Synedra ulna in Taejon-chon, Diatoma vulgare in Yudong-chon, Oscillatoria princeps, Scenedesmus gadricauda, Synedra ulna, and Diatom vulgare in Gap-chon. Standing crops of phytoplankton were from 2,076 cells/㎖ to 97,356 cells/㎖.