Effects Of High Temperature On Physiological Characteristics And Grain Yield Of Middle-season Indica Hybrid Rice During Flowering Period

The rice is one of the important grain crops in our country and it played a decisive role in the process of ensuring national food security. It was very important for rice yield and qulity at flowering of rice. The high temperature became very frequently in the rice area in the middle and lower Yangtze regions, especially the air humidity was less than30%and the temperature was higher than35℃which would make the transpiration rate increased, floral organ dysplasia, the pollination obstacles and the seed setting decreased finally. Particularly in recent years the high temperature became frequently in the middle and lower Yangtze regions in middle and later growth stages of rice. Therefore the high temperature made the grain yield and quality of rice instability which had been become the most important issue in the rice region.The objective of this study was to determine the physiological and biochemical reaction of middle-season indica hybrid rice between XLY6and SY63，under high temperature during flowering stage, a artificial climate box experiment was conducted. And to know more about the mechanism of physiology and photosynthesis which could provide the scientific knowledge for heat damage rice. Additionally，that could study the grain yield and composition of its when photosynthesis had changed. In the agricultural production，it could provide the reference to prevent the rice from hot stress and chosen heat-resistant rice. The experimental result was below.(1) The photosynthetic rate and chlorophyll content were all decreased after high temperature stress during flowing period. As the stress time going, the decreased amplitude was become great. In the6days of high temperature, the photosynthetic rate of XLY6andSY63had decreased23.87%,30.34%and the chlorophyll content of XLY6and SY63had decreased21.27%,27.77%. The XLY6had less decreased amplitude of the photosynthetic rate and chlorophyll conten than SY63.(2) The superoxide dismutase (SOD) enzyme activity of flag leaves in rice was deceased significantly with the high temperature time prolonged during flowing period. In the6days of high temperature, the SOD enzyme activity of XLY6and SY63had decreased5.80%and6.03%. The peroxidase (POD) and catalase (CAT) enzyme activity of XLY6was increased, while the POD enzyme activity of SY63was deceased significantly and its CAT enzyme activity deceased at first and then increased with the time prolonged.(3) The free proline, soluble sugar and soluble protein were significantly increased after high temperature stress during flowing period and with the time going the increased amplitude was become great. In the6days of high temperature, the free proline of XLY6and SY63had increased54.64%and27.60%, the soluble sugar had increased39.26%and33.80%,the soluble protein had increased3.95%and3.14%.The XLY6had more increased of the free proline, soluble sugar and soluble protein than the SY63.(4) The malondialdehyde (MDA) content of lipid peroxidation product increased significantly after high temperature stress during flowing period and SY63had more content of MDA than XLY6.(5) The fulfilled grains, seed setting rate,grain weight of fulfilled grains and grain yield were deceased significantly after high temperature during flowing period and with the time prolonged the decreased amplitude was become great. The Spikelets per panicle had no significant change after high temperature stress. In the6days of high temperature, the fulfilled grains of XLY6and SY63had decreased48.29%and48.02%, the seed setting rate had decreased48.81%and49.15%, the grain weight of fulfilled grains had decreased8.88%and18.38%, the grain yield had decreased54.18%and58.88%.The XLY6had less decreased amplitude of grain yield than XLY6.(6) The correlation analysis between physiological indexes and grain yield, seed setting showed that a significantly positive correlations were found between photosynthetic rate,chlorophyll content, SOD enzyme activity and grain yield, seed setting, the correlation coefficient with grain yield were0.968,0.940,0.797and the correlation coefficient with seed setting were0.971,0.942and0.761, while MDA had a significantly negative correlation with grain yield, seed setting and the correlation coefficient were-0.917and-0.900.