Abstract
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○ Title : Investigation of rice yield and quality change and development of adjustment technique to climate change
Air temperat...
○ Title : Investigation of rice yield and quality change and development of adjustment technique to climate change
Air temperature in Korea has increased by 1.5℃ over the last 100 years, which is nearly twice the global average rate during the same period. Moreover, it is projected that such change in temperature will continue in the 21st century. Impact of climate change on rice production would be bring about a tremendous effect on food supply in Korea. Therefore we conducted four studies as follows to assay impacts of climate change on rice growth and propose possible adaptation strategies for stable food supply under future climate change.
- 1st study : Investigation of rice yield and quality response to change of temperature and CO2 concentration
The objective of this study was to investigate the relationship between major climate change factors(temperature and CO2 concentration) and rice major growth characters(panicle number, grain number, grain weight, filled grain ratio, and fertility ratio), and establish the climate change evaluation system on the rice using crop growth model.
Firstly, it was found that magnitude of the positive effect of temperature on rice yield and quality was higher than that of the negative effect of CO2 concentration, where yield decline as climate change was mostly caused by low filled grain ratio due to high temperature during grain filling period rather than other growth characters. In addition, long-term high CO2 concentration exposure cause low photosynthesis efficiency and high plant temperature in rice by low CO2 conductivity and transpiration which make also alleviate the positive effect of CO2 concentration on the rice yield. Secondly, as a result of evaluation of climate change on the rice yield using crop growth model, it was found that the average production in 2071~2100 would be declined more under fixed cropping season(23.4~28.6%) than under chagned cropping season(0.2~7.4%). Analysis of variation suggested that temperature, CO2 concentration, cropping season, and rice maturing type contributed 59.8, 9.7, 11.8, and 1.7% of rice yield, respectively. In addition, regression analysis suggested that variation of rice yield was explained more by filled grain ratio rather than grain number under fixed cropping season was fixed while vice versa under changed cropping season.
- 2nd study : Investigation of rice yield and quality response to change of temperature and CO2 concentration
This study was investigated to find out relationship between grain-filling trait and physio-biochemical characteristics on the effect of high temperature on spikelet and leaf during grain filling stage. Donganbyeo and Ilpumbyeo were treated to high temperature(27±4℃) or control temperature (22±4℃) during grain-filling stage. Grain filling ratio, grain weight and perfect grain ratio of two varieties were decreased by high temperature but immature grain ratio was increased. The decreased ratio of grain flling and perfect grain of Dongan under high temperature were 8.8% and 23.7% and those of Ilpum were 23.7% and 41.8%, respectively.
The rate of grain filling rate and starch accumulation of high temperature-treated spikelet was faster and grain filling duration was shorten than the control temperature-treated spikelets. In the early stage of grain filling, α-amylase activity was significantly increased in high temperature-treated Ilpum but that of Dongan was not big difference. Concentration of maltose in high temperature-treated spikelet of Ilpum was continuously increased to late grain filling stage. Sucrose synthase activity of high temperature-treated spikelet of Ilpum in the early grain filling stage was higher than that of control temperature treated but lower than that of control treated.
Chlorophyll content of upper leaves in control temperature treated rice was gradually decreased during grain filling stage. But chlorophyll content of high temperature treated plant in the early stage of grain filling was higher than those of control treated rice. Chlorophyll a/b ratio of high temperature treated leaves was decreased during early grain filling stage and after than increased until late grain filling stage. Protein concentrations of leaves were showed similar pattern with change of chlorophyll content. Photosynthesis rate of high temperature treated 1st leaf in DAH 14 was higher but those of DAH 7 and 34 were lower than the control treated.
These results suggest that α-amylase activity during milky stage and low sucrose synthase activity from dough to maturity stage were a crucial factor for reduction of grain filling and perfect grain ratio under high temperature.
- 3rd study : Study on the variation of heading characteristics and the adapting cultivation technology as global warming in rice
This study was performed at Rice and Winter Cereal Crops Department of NICS during 2009 and 2011 to investigate the variation of heading characteristics by global warming and adapting cultivation technology of rice.
We checked the leaf emergence rate of chief rice cultivars which developed in Korea lately, here the difference of growing days from transplanting to the end of completion of flag leaf on main culm were 60~94 days. But cultivars which have similar growing daysshowed differenct leaf emergence rate and there were differences in emerged leaf number.
In each transplanting time, as the numbers of emerged leaf increased, the rice yield also increased generally. In late transplanting time, this tendency intensified. Here it is guessed that more emerged leaf number is favorable to secure enough rice yield. But in transplanting time on May 16 which have enough growth duration, early heading after short leaf growing days bring out ripening condition in high temperature and this lead to yield decrease.
As the temperature increases in transplanting time on June 1, the rice yield of Unkwangbyeo greatly reduced compared to those of transplanting on June 15 and June 30. In transplanting on June 15, the rice yield slightly increased in rising temperature condition. As the temperature increases, protein content continuously increased, conversely, amylose content continuously decreased. In early maturing cultivar, Unkwangbyeo, protein content was higher than other cultivars owing to ripening condition in high temperature because of early heading. But in late transplanting time, the protein content increased also owing to insufficient ripening because of late heading.
- 4th study : Rice panicle type modifying and heat tolerance screening for improving yield and quality under hight temperature
As elevated temperature by global warming deteriorates rice yield and quality, identifying heat tolerant rice genotype is necessary for developing high-quality and high-yielding japonica rice cultivar. This study was conducted to evaluate high temperature tolerance of Korean rice cultivars during the anthesis and ripening stage. High temperature during the ripening stage reduced ripened grain ratio, head rice ratio, whiteness and amylose content and increased protein content in most cultivars. Among 40 cultivars tested, reduction ratio of ripened grain under high temperature was low in Taebaek, Manpung, Gangbaek, Hwaan, Jangan, and Hwanam and reduction ratio of head rice and whiteness was low in Dongan and Daeya.
Ripened grain ratio under high temperature was negatively correlated with spikelet traits such as number of spikelets per panicle, number of total rachis branches, number of secondary rachis branches(SRBs), and number of grains setting on SRBs, which means ripened grain ratio decreased as the sink size increased. In high temperature treatment during anthesis, rice cultivar Taeseong, Manchu, Manna, Jinmi, Hwaseong, Manpung, Hwayeong, Dongjin, and Hanmaeum showed relatively high spikelet fertility. However, since daily flowering time is different not only among cultivars but also among the spikelets in a panicle, more precise screening is required to distinguish heat tolerance from heat avoidance.
