BackgroundResearch on the submergence stress of rice has concentrated on the quiescence strategy to survive in long-term flooding conditions based on Submergence-1A (SUB1A). In the case of the ripening period, it is important that submergence stress can affect the quality as well as the survival of rice. Therefore, it is essential to understand the changes in the distribution of assimilation products in grain and ripening characteristics in submergence stress conditions. However, such studies have been insufficient at the physiological and molecular biological levels.ResultsWe confirmed that the distribution rate of assimilation products in grain was decreased by submergence treatment. These results were caused by an increase in the distribution rate of assimilation products to the stem according to escape strategy. To understand this phenomenon at the molecular level, we analyzed the relative expression levels of genes related to sucrose metabolism, and found that the sucrose phosphate synthase gene (OsSPS), which induces the accumulation of sucrose in tissues, was decreased in the seeds and leaves, but not in the stems. Furthermore, the sucrose transporter gene (OsSUT) related to sucrose transport decreased in the seeds and leaves, but increased in stems. We also analyzed the biological metabolic processes related to starch and sucrose synthesis, carbon fixation, and glycolysis using the KEGG mapper with selected differentially expressed genes (DEGs) in seeds, stems, and leaves caused by submergence treatment. We found that the expression of genes for each step related to starch and D-glucose synthesis was down-regulated in the seeds and leaves but up-regulated in the stem.ConclusionThe results of this study provide basic data for the development of varieties and corresponding technologies adapted to submergence conditions, through understanding the action network of the elements that change in the submergence condition, as well as information regarding useful DEGs.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-5320-7) contains supplementary material, which is available to authorized users.

Italian ryegrass (Lolium multiflorum Lam.) was cultivated in a field experiment, on sandy loam soil of the Saemangeum reclaimed land, under different sowing rates and N fertilizer levels to estimate the optimum N fertilizer requirement and the most suitable sowing rate for seed production. The experiment was conducted in a split-plot design with four replications. The main-plots were four sowing rates of 10, 20, 30, and 40 kg ha -1 and sub-plots were five N fertilizer application rates of 0, 45, 90, 135, and 180 kg ha -1 . Harvest index decreased with increasing sowing and N fertilizer rate. The highest N use efficiency was obtained at 10 kg ha -1 sowing rate and 45 -90 kg ha -1 N fertilizer application rates. Maximum seed yield of Italian ryegrass based on the regression curve of N fertilizer application level was 102 kg ha -1 and was decreased with further N application. Economically, optimum rates of N application ranged from 70 to 101 kg ha -1 depending on the sowing rate. Results from this experiment, could therefore inform producers of the best combination of sowing and N fertilizer rates needed to increase profitability of Italian ryegrass seed production alongside preventing N loss. However, further research will be necessary to elucidate on increasing seed quality and stability of cultivation under various environmental conditions.

Although the forage production area of Italian ryegrass is expanding in Korea, most of the seeds are imported from abroad. This study was conducted to examine seed productivity of domestic varieties of Italian ryegrass under different soil salinity in reclaimed tideland. Compared to 0.1% of soil salinity, the emergence rate at 0.2 -0.3% salinity decreased by 7%. The number of ear and grain weight also decreased at the 0.2 -0.3% of salinity, eventually leading to 23% decreases in seed yield compared to the 0.1% salinity. There was no significant difference in yield components among cultivars, but Greenfarm showed slightly higher yield components than other cultivars. Therefore, when domestic cultivars are harvested in reclaimed land, it is expected to increase the self-sufficiency of domestic seeds and to replace imports of foreign seeds.

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Influences of various soil chemical properties on the algae growth (Chl-a concentration) at the paddy field were statistically analyzed using soil and water samples collected from 2016 to 2018 in June. As a result of correlation analysis between soil chemical properties and Chl-a concentration, significantly positive relationships were observed in pH, EC and SiO2. To identify the key soil chemistry variables and predict Chl-a concentration, factor analysis was done and three principal components (PCs) with eigenvalues > 1 were found, which accounting for 60.9% of the original variance. The PC1 included Mg 2+ , Ca 2+ and Avali.-P. The PC2 included pH, Na + , K + , and Avail.-SiO2. PC3 included OM and T-N.According to the result of linear regression analysis based on the factors by factor analysis, the total explanation amount was 18.0% and only PC3 had an significant influence on the decrease of Chl-a concentration. These result will be used for soil management to prevent algae blooms at rice paddy field.