| Rice is increasingly suffered from extreme temperature stress with ongoing climate change.As one of the most important rice production areas in China,it is predicted that extream weather will occur more frequently in Mid-reaches of the Yangtze River where heat stress has posed a serious threat to rice production.Significant progress has already been made in understanding formation mechanism of heat stress in rice,mapping QTL for heat-tolerance,effects of heat stress on grain yield and quality,and agronomic measures against heat stress.However,little information about the occurence of heat stress,disaster degree of rice under heat stress,conditions for heat injury,and difference among different rice cultivars in the pratical rice production or under paddy condtions has been documented.In essence,the occurence of heat stress is the result of specific areas and specific meteorological conditions coincided with specific cultivars and critical growth period.Hence,reflecting the occurrence laws of heat stress exactly under regional or paddy conditions is the original point of research on heat stress of rice,which cannot be replaced by those laboratory studies.Experiments were conducted in Jingzhou city,located in the middle reaches of the Yangtze River where heat stress occurs frequently in summer.In 2016 and 2017,the occurrence of heat stress,the extent of heat injury in rice,the conditions for heat injury in rice,the difference among rice cultivars exposed heat stress and the meteorological characteristics when heat stress occurred were investigated by means of surface investigation,field test and field monitoring.Over the past two years,serious heat stress has occurred at the reproductive growth stage of single season rice.In 2016,after the occurrence of heat stress,a comprehensive survey of large scale and multiple varieties on the surface was carried out in Jingzhou and Jingmen,respectively.In 2017,the test of heat-tolerant of new rice varieties and new strains were conducted in Jingzhou.In 2016,the overall heat resistance of the new rice varieties under the large field conditions was observed in the different provinces of the middle reaches of the Yangtze River(Jingzhou of Hubei,Taoyuan of Hunan and Lujiang in Anhui).In addition,the rice canopy was monitored in real time by MINCER(Micrometeorological Instrument for the Near-Canopy Environment of Rice)under the open field conditions,so as to obtain the micrometeorological parameters of rice heat damage under field conditions.The main results are as follows:1.The results of 2016 years' survey showed that the overall disaster degree of the80 rice varieties in this survey was different,and the damage degree of most rice cultivars was first level(75% > seed setting rate?60%),and the remain was second level(seed setting rate < 60%).The main damaged rice cultivars were hybrid rice and some were inbred rice.The time of heading of main damaged varieties and heat stress occurrence were between July 22 nd and 1st August.The weather conditions in this period were: daily average temperature was 31.5?,relative humidity 70%.2.In 2017,the time of heat stress occurred was from 20 th to 28 th July.The heading time of most tested rice was in late July,and they exposed at least 3 days heat stress before heading or after heading.The ratio of the seed setting rate below 75% of new varieties and new strains was 13,accounting for 27.7% of all tested rice varieties,and the average seed setting rate of those rice varieties(seed setting rate below 75%)was 70.9%.The average seed setting rate of remained rice varieties was 82.2%.3.In 2016,the occurrence time of heat stress in Jingzhou,Taoyuan and Lujiang were mainly in late July.In Taoyuan and Jingzhou,the number of days exposed to heat stress before and after heading of new rice varieties was more than that in Lujiang.In the three ecological areas,the seed setting rate decreased after heat stress before and after heading,and the decrease was higher than that before or after the heading.The harm of heat damage to rice seed setting rate has cumulative effect.The longer the duration of heat damage,the greater the decrease of seed setting rate.Some varieties only experienced 2d heat stress before heading,and the seed setting rate was decreased significantly.4.The temperature among inside canopy,above canopy and open area was significantly different under normal temperature weather.The temperature value increased from inside canopy,above canopy and open space.The temperature inside caopy and above canopy of the Quanliangyou 681 is 1.5 degree and 0.5? respectively,lower than that in the open space,and the temperature inside canopy and above canopy of IR64 variety is 1.4? and 0.5? lower than that in the open ground.Similarly,the relative humidity among the three locations was also significantly different.The humidity inside the canopy and above the canopy of Quanlingyou681 canopy is 12%and 4.4% higher than that in the open land,and the humidity insde the canopy and above the canopy of the IR64 variety was 10.9% and 4.4% higher than that in the open land.Under heat stress scenario,the temperature and humidity inside the rice canopy are significantly different from those in the atmosphere.During heat stress period,the average temperature inside the canopy was 1.6 degrees lower than the air temperature,and the average relative humidity in the canopy was 10% higher than that in the air.In summary,under the typical high temperature years,the heat damage of rice at the heading stage in Jingzhou and Jingmen areas is more common,and the main varieties are hybrid rice and some conventional rice.It should be combined with the characteristics of the heat damage of the Yangtze River basin to speed up the heat tolerance breeding process of new rice varieties and establish the heat resistance identification of the new varieties of fast batch varieties.Method system.The heat tolerance of some new varieties(lines)in the middle reaches of the Yangtze River still has a general problem,which is not enough to resist the heat hazards occurring in reality.In the future breeding work,the current breeding policy should be revised in time.Rice breeding should aim at improving heat tolerance,yield and quality in synergy,and the research on improving the heat resistance of rice should be emphasized.In the future,when using the mathematical model to simulate the meteorological data,we should take the rice canopy as the criterion,so as to improve the accuracy of model prediction. |
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