In the process of growth and development of rice, it is often encountered low temperature and lack of light, resulting in poor seed germination, grub, seedling growth, fertility atrophy, leaf abruption, apical spikelet degradation, reproductive delay, infertility Cold damage, such as poor maturity, ultimately leads to a reduction in yield. According to the characteristics of rice chilling injury, chilling injury is divided into obstacle-type chilling injury, delayed chilling injury and mixed chilling injury. The chilling injury affecting rice production will occur at different stages of rice growth. The degree of chilling damage will not only be determined by the temperature, cold and low temperature duration, sunshine and other meteorological factors and rice varieties and types, but also determined by the rice growth and development period. Some varieties are sensitive to low temperatures throughout their growing period; some varieties are only cold during some growth periods; some also have cold tolerance throughout the growing season. Related Products: Germplasm Resource Container Tester
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China is the country with the highest total japonica rice production in the world, and it is also the country with the largest cultivated area. More than 90% of the cultivated area of ​​japonica rice in cold regions is distributed in Heilongjiang Province. Therefore, Heilongjiang is the main body of the japonica rice cultivation area in China. This study selected the major rice cultivars in Heilongjiang Province in order to provide a basis for further studies on the cold tolerance of different rice growth cultivars in Heilongjiang Province.
1 Materials and Methods
1.1 Materials The tested rice varieties were Kongyu 131, Qinjiandao 6, Wandao 12, Longjing 26 and Longjing 29. The artificial climate room is produced by Zhejiang Top Instrument Co., Ltd.
1.2 Methods
1.2.1 Cold-tolerance treatment at germination stage Seeds were disinfected with 70% ethanol for 1 min, rinsed with distilled water and soaked for 1 d. 60 seeds per species were selected and placed in a petri dish with a diameter of 9 cm and filter paper on the bottom, and placed at 15°C. In the climate chamber, deal with 15d. At the same time set the normal temperature control. Measured index: germination rate /% = number of germinated grains / total number of test grains × 100.
1.2.2 Treatment of cold tolerance at seedling stage Three-leaf-age seedlings grown at room temperature are placed in a 5°C artificial climate chamber, relative humidity: 70% to 80%, light intensity: 20,000 to 30,000 lx, 12 hours, 7 days treatment, room temperature Restored 6d. According to the chilling grading standard at seedling stage, the indexes for determining the cold tolerance of rice were determined.
1.2.3 Cold-tolerance treatment methods at booting stage The varieties are planted in plastic pots with a diameter of 13.5cm and a height of 11.5cm after being raised in the greenhouse at the age of 3 leaves. Each pot has 3 holes and 3 for each hole. Six pots of each variety were transplanted. The plastic pots were planted in the paddy fields and the water surface was not over the pots. Three pots were treated at low temperature during the booting stage and three pots were used as controls. The low-temperature treatment conditions were: artificial climate box treatment at 15°C, relative humidity 80%, light intensity: 10,000 lx, and processing time 7 days. The indicators include plant height, grain weight per plant, seed setting rate and 1000-grain weight in mature rice. Use spss 13.0 software for data statistics. 
2 Results and Analysis
2.1 Cold tolerance at germination stage From Table 1, we can see that the chilling tolerance at the bud stage of the tested cultivars was: Kongyu 131>Jianjiandao 6>Japonica 12>Longjing 29>Longjing 26.
2.2 Chilling tolerance at seedling stage The low temperature chilling at the seedling stage mainly leads to poor bud emergence, weak seedlings, susceptible blight and delayed transplanting. According to the grading standard of rice seedling cold tolerance, the test results were empty Yuu 131 (Grade 1), Longjing 29 (Grade 3), Japonica rice 12 (Grade 4), Longjing 26 (Grade 5), and Qin Jiandao 6 ( Level 7).
2.3 Cold tolerance at booting stage As shown in Table 2, the low temperature treatments of the tested rice varieties were lower than the control in plant height, grain weight per plant, seed setting rate, and 1000-grain weight, indicating that the low-temperature treatment of rice at the booting stage had the effect on rice growth. And the formation of grain has an effect. There was a significant difference in the performance of the test cultivars on the seed setting rate. The seed setting rate of all varieties under low temperature treatment was empty Yuyu 131> Longjing 29> Japonica 12> Yujiandao 6> Longjing 26.
3 Conclusions The results of the study showed that the chilling tolerance at the bud stage of the tested cultivars was: Yuyu 131>Jianjiandao 6>Japonica 12>Longjing 29>Longjing 26. The cold tolerance at the seedling stage was Kongyu 131> Longyan 29> Japonica 12> Longjing 26> Qijiandao 6. Low temperature at booting stage can lead to a decrease in plant height, grain weight per plant, seed setting rate and 1000-grain weight of all varieties. The seed setting rate of low-temperature treatments is: Yuyu 131> Longjing 29> Japonica 12> Yujiandao 6> Longjing 26.
Through the low-temperature treatment of different rice varieties at different growth stages, the results showed that there were differences in the response of the varieties to low temperatures, and the cold tolerance of the same variety at different growth stages was different. The comprehensive test results showed that the tested varieties of Yuyu 131 and Longjing 29 had relatively strong cold tolerance at the bud stage, seedling stage and booting stage.
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Artificial climate box simulated low temperature environment to test the cold resistance of rice
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