Han-Yong Jeong

Statistical assessment of the late marginal heading date for normal maturation of temperate japonica rice in South Korea

The late marginal heading date (LMHD) for normal maturation has been assessed to infer the range of late transplanting date and applicability of a new cropping system. A minimum threshold temperature for grain filling can be used to determine the late marginal heading date that would allow normal maturation. In this study, a statistical procedure was developed to determine the threshold temperature for 40 days of the grain-filling period. The threshold temperature was chosen to be the minimum temperature at which grain-filling ratio and weight are minimally affected. To identify the threshold temperature, grain-filling ratio and weight, which were observed at two sites for 2 years in Korea, were compared with a range of cumulative temperature during 40 days in the late season. As a result, cumulative temperature of 800℃, which is equivalent to, on average, 20℃ during 40 days of grain-filling period, was determined to be the threshold temperature for normal grain filling in the late season. The LMHD for normal maturation was also determined from cumulative probability density function of dates from which the threshold temperature of 800℃ was met during the last 15 years as well as 33 years. Our results suggested that it would be better to use the cumulative density function of those dates derived from the last 15 years rather than 33 years because current climate conditions could be better represented by the density function derived from recent years.

Emergence Characteristics of Weedy Rice Collected in South Korea

In order to provide basic data for efficient control of weedy rice, we analyzed emergence rate of 100 weedy rice genetic resources collected in South Korea according to growth temperature and soil burial depth. Analyzing of emergence rate using low dormancy weedy rice genetic resources, emergence was increased at 12 and 14°C of mean temperature condition. When calculating the effective accumulated temperature above 10°C, emergence rate increased 0.6% and 0.5% in 1 cm and 3 cm of soil depth, respectively according to increase of 1°C. However it reduced as 0.28% in 5 cm of soil depth condition. Analyzing of emergence rate using high dormancy weedy rice, red rice showed 55%, 46%, 41% of emergence rate in 1 cm, 3 cm and 5 cm of soil depth condition, respectively. However those of white rice decreased as 10%, 8% and 5.7% in 1 cm, 3 cm and 5 cm of soil depth condition, respectively. Relative emergence, assuming the final emergence rate as 100%, reached 80%, 90% and 100% when effective accumulated temperature was 83-112°C, 100-123°C, 148-160°C respectively.

Selection of the Korean Rice Cultivars Having Adaptable Heading Characters in Subtropical Regions

[Introduction] Japonica rice is recognized as the premium rice compared to Indica rice in tropical region especially in Philippines. Therefore development of adaptive Japonica rice variety in tropical region has been actively conducting to increase income of local farmers in the tropical regions. Here we tried to investigate the basic vegetative phase and temperature sensitivity during sensitive phase among Korean major cultivars to recommend the Korean rice cultivar which shows the suitable heading characters in tropical region then help to develop adaptive rice cultivars in tropical region.