| With rapid industry development and frequent human activities, atmospheric carbon dioxide concentration remains rising, as well as the earth surface temperature. It is estimated that the earth surface temperature will have increased by 1.4-5.8℃by the end of this century, while rising speed of night temperature will be 3 times than that of daytime. Rice (Oryza sativa L.) is one of the important food crops grown across the world. Most of the rice is being grown in regions where current temperatures are already close to optimum for its productive. Therefore, any further during increase in mean temperature or period of short episodes of high temperatures during sensitive stages may decrease yields. Thus, identifying and developing high temperature tolerant cultivars will be important to meet the demand for food production in persent and future climate. Field experiments were conducted at IRRI, in the 2009WS,2010DS and WS and 2011DS to determine genotypic variation in sensitivity to warm nighttime temperature.36 varieties originating from and widely grown in different countries were selected according to their sensitivity to heat stress for the four consecutive seasons. These varieties were grown in temperature-controlled field chambers. An increase of 4.1,3.9,4.0 and 3.8℃in night temperature was imposed on the plants from 40 to 120 days after transplanting, starting from 1900h until 0600h. The main results of the study are listed below:1. The examination result of field chamber system on the 3 days before transplanting and 36 days after transplanting shows that, the difference of atmosphere humidity, CO2, VPD, and water temperature inside and outside of the chamber is slight; the difference of temperature and humidity is not significant, even in different distribution, different height and different locations of the same chamber. The exhaust funs applied in this study have a good effect on controlling humidity and CO2 concentration.The humidity of high temperature treatment after shutting the exhaust funs decreased by nearly 30% than normal temperature treatment. The air conditioner equipments work to heat or cool down progressively. Keeping temperature stable last for 5h on the 3 days before transplanting and 3h on 36 days after transplanting, respectively, that connects with the atmosphere temperature. The effect of field chamber’s comprehensive low-temperature-controlling is better than high temperature. The index of the field chamber system tends to be normal under low temperature controlling.2. Significant differences in grain yield between the LNT and HNT treatments were observed in the all experiments, Varietal differences in grain yield were significant in the all three experiments, but there were no statistically significant temperature×variety interactions. Average yield of LNT was 455.6 g m-2,681.3 g m-2,487.6 g and 579.0 g m-2 in 2009WS,2010DS,2010WS and 201 IDS, respectively. Average yield of HNT was 379.3 g m-2,619.2 g m-2,440.7 g m-2 and 532.9 g m-2 in 2009WS,2010DS,2010WS and 2011DS, respectively. Grain yield decreased by 16.7%,9.1%,9.6% and 8.0% than LNT in the four consecutive seasons, respectively. Grain weight and harvest index was significantly higher in LNT than HNT in the all four experiments.Significant difference in grain filling between the LNT and HNT treatments was observed in 2009WS, with values of 73.8% and 69.7% in LNT and HNT, respectively. Significant difference in spikelets per panicle was observed between LNT and HNT in 2010DS and 201 IDS.3. Significant differences in total dry weight between the LNT and HNT treatments were observed in the all experiments. Total dry weight decreased by 9.2%,5.3%,5.5% and 7.9% than HNT for the four consecutive seasons, respectively. Varietal differences in growth duration were significant in all four experiments. There are no significant interaction effects on variety and temperature in all four experiments. There were significant effects of temperature on crop growth rate (CGR), CGR decreased by 0.8 g.m2.d-1,0.4 g.m2.d-1,0.5 g.m2.d-1 and 0.4 g.m2.d-1 than HNT for the four consecutive seasons, respectively. Plants in the LNT achieved higher total dry weight because of it’s with higher CGR than HNT. Plant height was significantly different between LNT and HNT in the three experiments expect 201 IDS. NT Plants were shorted than HNT by 5.9, 2.2, and 2.5cm for the three consecutive seasons, respectively. Significant differences in panicles number per m2 between HNT and LNT treatments was only observed in 201 IDS, There were no significant effects of temperature on crop phenology.4. Classify the 36 varieties by three methods determine genotypic variation in sensitivity to warm nighttime temperature. (1) Classify the varieties by yield decrease range. The yield of experimental varieties decreased -0.8%-26.8%. Ciherang, Sambha Mahsuri, X21, IR6, PSBRc18 and other 18 varieties are sensitive to hight night temperature, their yield decrease range is 10.4%-26.8%. N22, IR20 and other 11 varieties are insensitive to hight night temperature. Among which,7 are insensitive at high-yielding level,6 are insensitive at low-yielding level. (2) Classify the experimental varieties by decrease range of grain filling rate. The grain filling percentage of Saunfi, Gharib, Swarna, Sambha Mahsuri, PSBRc4 and other 7 varieties which are sensitive to high night temperature decreased 5.0-15.5%. N22, IR26, IR8, IR22, NSICRc112 and other 19 varieties are insensitive to high night temperature. Among the 24,16 are insensitive to high-grain filling rate percentage,8 are insensitive to low-grain filling percentage level. (3) Classify by decrease range of spikelets/panicle. The spikelets/panicle of Ciherang, PSBRc18, IR22, IR60, Sambha Mahsuri and other 15 varieties, which are sensitive to temperature, decreased by 5.8%-17.4%. N22, PSBRc4, Saunfi and other 13 varieties are insensitive to high night temperature. Among the 16,3 are insentive at high spikelets/panicle level,13 are insentive at low high spikelets/panicle level. Comprehensively considering yield and yield components, PSBRC82, IR24, IR8, OM2517, IR64, IR56, IR20 and N22 have the ability to resist high night temperature. Screening of breeding materials with more tolerance to high night temperature is an efficient way to the development of new varieties for a warmer world.5. Varieties show different sensibilities are sensitive to high nighttime temperature. The analysis of classifying varieties by cultivar years based on recent 50years’research showed, the yield of 2000S’ variety improved 49.9% than 1960S. However, the new variety has no advantage in resisting high nighttime temperature over the old variety. Yield potential of the new variety improved greatly in the way of yield components, including spikelets panicle-1, totoal dry weight, harvest index and crop growth rate. |
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