| Crop production is severely affected by high temperature resulted from global warming. It is reported that night temperature increased more than day temperature. When the environmental temperature is higher than the threshold temperature under which crop can tolerate, crop growth will be influnenced at any stages of its life. Global warming makes the crop suffer high temperature stress more frequently. Double season rice (early and late) and single season rice (middle season) are planted widely in the middle and lower reaches of the Yangtze River, which is of immense importance to the food security in China. High temperature occurrence is easy to come across in the middle and lower reaches of Yangtze River, especially for the middle season rice. Several hours of extremely high temperature in the flowering period may be deathful to the spikelets, which will result into catastrophic outcome.Therefore, in this passage, we try to study:(1) the effect of different seeding dates on rice yield and quality, (2) the effect of high temperature on rice yield of heat tolerant cultivars (or lines) and heat susceptible cultivars (lines), (3) different effects on rice yield and yield components from high temperature in different growth stages (panicle initiation stage, flowering stage, and grain filling stage), (4) the physiological mechanisms of the effect of high temperature on rice yield. Field experiment and pot experiment were conducted in 2009 and 2010, respectively. The main results are as followings:(1) Days with temperature more than 35℃and the average temperature over the whole growth period increased in the early seeding date, and they both correlated with yield and grain filling percentage negatively and significantly. There was a significantly positive relationship (P<0.01) between chalky rice percentage, chalkiness area, and chalkiness degree and daily average temperature, daily maximum temperature, daily minimum temperature in the grain filling period.(2) Rice yield and grain filling percentage declined in the early seeding date for majority of the cultivars used in this experiment, and the decline in grain filling percentage for Indica cultivars was more significant than that for Japonica cultivars. But biomass and plant height declined as seeding date was delayed, and the effect on Indica cultivars was greater than that on Japonica cultivars. Responses of yield and yield components to seeding date treatments for different cultivars varies due to the different growth period and subsequent different environmental factors for different cultivars.(3) High temperature in panicle initiation period affected rice yield tremendously and negatively. For T219, a heat susceptible cultivar, grain yield decreased by 55.0% and 56.4% in high day temperature and high night temperature treatments, respectively, when compared with the control. On the contrary, for SY63, a heat tolerant cultivar, grain yield and grain filling percentage declined by 41.5% and 36.0%, respectively, in the high day temperature treatment. Generally, high daytime temperature had a bigger influence on grain yield than nighttime.In addition, high daytime temperature decreased the chemical quenching (qp),ΦPSⅡ, Fv/Fm, and Fv'/Fm'. There were no significant changes in these indices for SY63 under two temperature treatments.(4) At flowering stage, yield and grain filling percentage decreased significantly due to high temperature treatment both in daytime and nighttime. Yield of T219, T226, LYPJ and SY63 decreased by 67.1%,34.3%,58.3, and 33.8% in night temperature treatment, respectively. Above ground biomass also decreased due to high temperature in nighttime. In daytime temperature treatment, yield of T219, T226, LYPJ and SY63 decreased by 91.9%,92.1%,98.7%,75.4%, respectively. High temperature both in daytime and nighttime at flowering stage decreased the vitality of pollens. The decrease in pollen vitality was more significant than the other cultivars. On the fourth day of temperature treatment, pollen vitality was decreased by 35.7% and 30.6% for T226, respectively. High pollen vitality was achieved for SY63 under both the two temperature treatments.(5) High daytime temperature at flowering stage decreased the content of Zt and IAA.(6) Compared with temperature treatment in panicle initiation stage and flowering stage, yield and grain filling percentage decreased slightly, but grain weight decreased significantly at grain filling period. With high daytime temperature at grain filling period, T219, T226 and SY63 had a lower brown rice rate and polished rice rate. High nighttime temperature had little effect on the milling-related characteristics. |
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