Effect Of High Temperature In Different Periods During Rice Reproductive Stage On Grain Yield And Rice Quality

High temperature become frequently with global warming. It is big challenge to sustainable improve rice yield and rice quality to satisfy the increasing need in a warming condition. Field and pot studies were conducted in 2008-2011 to select rice varieties with different sensitiveness to high temperature and to investigate the effect of high temperature in different periods of reproductive stage on grain yield and rice quality. In 2008,104 varieties from rice core collection were evaluated under field to select varieties that were apt to the climate in this region and have wide representativeness on rice yield and rice quality. Then,40,10 and 7 varieties were chosen to sowing dates experiments in 2009-2011. Based on various responses to high temperature on yield and rice quality, groups were divided from all varieties. Moreover, the most important high temperature periods for effects on yield and rice quality was analyzed for different groups. Then 2 typical varieties with different response to high temperature were chosen based on sowing date experiments in a pot experiment in greenhouse in 2011. Four temperature treatments, normal temperature (CK), high temperature in daytime (HD), high temperature in nighttime (HD), high temperature in daytime and nighttime (H(D+N)), were set up by temperature controller in greenhouse from full heading date to mature. Differences and similarities of high temperature response on grain yield and rice appearance quality between typical varieties were examined. Otherwise, effects of source-sink structure on yield and rice quality in high temperature condition was analyzed by synthesis. The following results were obtained:(1) There were very big ranges on indexes such as plant type, yield and rice quality among selected 104 varieties from rice core collection in this research. Most investigated rice quality indexes were normal distribution on variety numbers, so that these varieties had wide representation. Based on some threshold on duration from seeding to heading, plant height, lodging, varieties which can be apt to climate the climate in this region were chosen. The chosen 39 varieties were also widely representative.(2) All varieties were divided to 4 groups with two-dimensional quadrant method based on maximum yield and yield gap among different sowing date. Yield of varieties in group 1 was decisive from grain filling rate and spikelets per panicle, which were sensitive to environment. One week before heading and one week after heading were the key period for effects of high temperature on yield. There is abvious negative correlation between spikelets per area and average daily mean temperature during one week before heading; Grain filling rate depend on effective accumulated temperature over 35℃ during one week after heading. Yield was not influenced by high temperature during the day, but yield will decline a little with high temperature at night, and yield will decline remarkable in high temperature during all day. The decrease of Grain filling was the main reason of yield decline in the condition of high temperature at night or during all day. Otherwise, Reduce of spikelets per plant and grain weight was also the reason for yield decline. It was a good research basic for high yield breeding that varieties with stable high yield were selected from rice collection and some generalized varieties in this research.(3)Chalkiness was the most sensitive to high temperature after heading among rice quality indexes. There were obvious correlation with chalkiness and most other rice quality indexes. Based on threshold of maximum chalkiness and chalkiness range among different sowing date were 15%,4 groups were divided with two-dimensional quadrant method. Chalkiness was response uniform to heading date among varieties in the same group. Temperature in the second week after heading was highest in the year, in which sowing date, chalkiness was highest. It indicated that the second week after heading was the most important period. When the mean ratio of rice length across different sowing date was bigger, maximum chalkiness will be larger across different sowing date for all varieties. Head rice was also reduced with the chalkiness increased in high temperature, so that rice commodity value will have big negative impact in high temperature. When the effects of high temperature during daytime or nighttime was analyzed:all rice quality indexes had no effects to high temperature during daytime; Only appearance quality of sensitive varieties were impacted by high temperature at night; Processing quality, appearance quality, cooking and nutrition quality of sensitive varieties were all effected obviously by high temperature during all day. But different rice quality indexes of one variety may have different sensibility to high temperature.(4) High temperature during flowering reduced pollen fertility and grain filling, so that sink was reduced. Leaf was not injured by high temperature during filling stage, so that source had no directly effects. Yangdao6 and Chengnongshuijing were a pair of typical type varieties on response to high temperature. There were many differences in source-sink structure between the two varieties. Yangdao6 was large-spike cultivars, but Chengnongshuijing was multi-spike cultivars. Yangdao6 had more inferior spikelets compared with Chengnongshuijing. But there was no different in grain shape between the two varieties. Range of dry matter accumulation after anthesis, dry matter transport before anthesis and ratio of spikelets and leaf area had nagetive correlation with yield range across different sowing dates. This may because source-sink structure of variety had more self-adjustment capacity, yield can be more stable. Grain filling of inferior grain was more responsible to high temperature, and response of grain filling to high temperature was weak when ratio of spikelets and leaf area become small. But chalkiness of Chengnongshuijing was responsible to high night temperature, and the impact on super grain was higher than that of inferior grain.