Effects Of Low Temperature Stress At Flowering And Filling Stages On Grain Quality In Rice

With the development of modern rice industry and the increase of people’s requirements for rice quality,the grain quality of rice has attracted wide attention from producers,food departments,commercial departments,processing enterprises and even consumers.The improvement of rice quality,and its relationships with ecological environments have also been the focus of current research.Rice quality is a complex comprehensive trait,which is not only affected by genetics,but also by the ecological environment.With the global warming,the frequency,intensity,and duration of low temperatures increased.The frequent occurrence of low temperatures has exacerbated the instability of rice production systems and reduced rice grain quality.Therefore,in-depth analysis and quantification of the impact of low temperature stress on the formation of rice grain quality can provide effective support for the prediction and evaluation of rice grain quality in the context of climate change.This study aims to investigate the effects of the treatments of low temperature level and duration during different key stages on the formation of rice grain quality by using two varieties with different temperature sensitivities（Huaidao 5 and Nanjing 46）.The specific research results are as follows:（1）With the increase of the low temperature intensity,the protein content in grains increased and the starch and its components decreased.The lower part of panicle was most affected by low temperature,the low temperature strss during full flowering stage had the greatest effects on protein,and the low temperature stress during grain filling stage had the greatest effects on starch and its components.Comparing the two varieties,the change of accumulation dynamics of Huaidao 5 after low temperature treatment was significantly lower than that of Nanjing 46.The relationship between the accumulation of protein,starch and its components and growth degree days（GDD）were developed by using logistics equations,the results showed that accumulation characteristic parameters has a great correlation with ACDD（accumulated cold degree days）.As ACDD increased,the maximum accumulation（K）,the maximum accumulation rate（Rmax）,average accumulation rate（Rmean）and cumulative active growth phase（D）of Huaidao5 and Nanjing 46 declined significantly comparing to the control treament,the maximum accumulation rate（Rmax）affected by low temperature was the largest.After low temperature treatment,the grain protein accumulation characteristic parameters had better correlation with accumulated cold degree days based on soil temperature（ACDDs）,and starch and its component accumulation characteristic parameters had better correlation with accumulated cold degree days based on air and canopy temperature（ACDDa and ACDDc）.（2）After low-temperature treatment,the nutritional quality,processing quality,appearance quality and RVA characteristics of rice grains in the mature stage were all significantly affected,and the adverse effects of low temperature on quality in the grain filling stage was significantly greater than that in the early flowering stage and the full flowering stage,and the effect of low temperature on the quality of Nanjing 46 was significantly greater than that of Huaidao 5.With the decrease of temperature level and temperature duration of low temperature,the protein content increased significantly,and the starch content and its components generally showed a downward trend,however,the amylose content under mild low temperature treatment decreased slightly or even slightly increased.After low temperature treatment,the percentage of brown rice,the percentage of milled rice and and the percentage of milled rice rate were significantly reduced,the chalky rate and chalkiness were significantly increased,and the grain surface area was reduced,but the ratio of grain length to width didn’t change significantly.Regard to the characteristics of RVA after low temperature,the peak viscosity,breakdown value significantly decreased,the hot paste viscosity,final viscosity and setback value of increased significantly,consistency value didn’t change significant.The linear relationships between the relative contents of protein,starch and their components of rice grains during maturity and ACDD（ACDDa based on air temperature,ACDDc based on canopy temperature,and ACDDs based on soil temperature）were developed.Among them,the relative content of rice grain protein and ACDDs were relatively higher,the relative content of starch and its components were highly correlated with ACDDa and ACDDc,the correlation of grain processing quality,appearance quality and RVA characteristics with ACDDa,ACDDc,ACDDs were not significant.It was concluded that the impact of low temperature stress on rice grain quality,the air temperature,canopy temperature and soil temperature should be comprehensively consided.