| Rice grain quality usually includes milling,appearance,nutrition and taste qualities.Rice grain quality is an important indicator to evaluate rice varieties.With the development of social economy,rice quality is gaining prominence in daily consumption and import/export trade.Because of the soft and sweet taste,japonica rice occupies an important position in the high-quality rice market.Northeast region of China is the main production area of japonica rice.Both the sown area and total production of japonica rice in this region account for more than 50% of the country’s,and the rice output rate has also remained above 50% all the year round.Therefore,this region is considered to be the most important japonica rice production and commodity grain base of China.The middle region of Northeast China(42°-44°N)locates in the world’s golden rice belt,where is the core area for producing high-quality rice in China.In this study,japonica rice varieties with large planting area and different quality characteristics in the core region for high-quality japonica rice production were selected to clarify the effects of climate conditions and soil conditions on the formation of rice grain quality.Also,transcriptome analysis of different quality varieties was carried out to investigate the material basis,structural basis and molecular mechanism of the formation of high-quality rice grain.The results of our study provide scientific evidence for selecting the varieties suitable for cultivation in the core region for high-quality japonica rice production,and provides theoretical basis for developing elite rice varieties with geographical characteristics.Moreover,our research contributes to ensure the sustainable development of high-quality rice production in this region.Three representative areas(Gongzhuling,Changchun and Wuchang)in the middle region of Northeast China were selected for pot trials and field trials from2017 to 2018.Pot trials were conducted at each area using soil from the three sites.The japonica rice varieties including Jigeng 809,Wuyoudao 4 and Tong 35 were used to explore the roles of different climatic and soil conditions in rice quality formation.The transcriptome changes responding to different genotypes and environments were analyzed in this study.At the same time,eight rice varieties,including Jigeng 809,Jigeng 812,Jigeng 511,Wuyoudao 4,Ji B 2008-1853,Qiuguang,Jiyugeng and Tong35 were selected and simultaneous planted in the field in the three sites to explore the effects of light and temperature conditions on the formation of rice quality.From 2019 to 2020,the japonica rice varieties including Jigeng 816,Wuyoudao 4,Jigeng 81,Jida718,Jigeng 511,Jigeng 809,Tongxi 933,Qiutianxiaoding,Ji B 2008-1853,Jiyugeng,Tong 35,and Qiuguang were used to further explore starch particle size distribution and its role in rice quality in this region.And the significance of viscosity characteristic and thermodynamic properties in the evaluation of rice cooking and eating quality were investigated in this study.The main results are as follows:1.The combined effect of genetics and environment on rice grain quality formation.Results of soil swap potting trials show that rice quality is comprehensively affected by genetics,climatic conditions,soil characteristics and their interactions under normal cultivation conditions.The analysis of variance component estimation show that genetic factors are the basis for the formation of rice grain quality,and the effect of climatic conditions on rice grain quality is much greater than that of the soil conditions.However,the climatic conditions of different experimental sites have different effects on different quality characteristics of rice grain.Climatic conditions at Wuchang area are beneficial for the development of higher milling quality of rice grain,and climatic conditions at the Gongzhuling area helped to form higher appearance and taste quality.Soil conditions at Changchun test site promotes the formation of higher milling quality of rice grain,however soil conditions at Wuchang test site is more likely to produce rice grain with higher appearance quality.However,the nutritional quality and taste quality are less affected by soil conditions,because there are no significant differences among the three soil types.2.Effect of light and temperature on rice grain quality formationLight and temperature conditions at different test areas were significantly different during the rice filling period.The main performance was that the average daily temperature(AT)at the Wuchang area was lower,the daily temperature range(RT)at the Gongzhuling area was larger but the photosynthetically active radiation(PAR)was lower,while Changchun area had a narrower RT but higher PAR.The results of correlation analysis show that it is beneficial to reduce the chalkiness and accumulate proteins in rice grain under the conditions of higher PAR,AT and narrower RT.However,the formation of better taste quality of rice requires lower PAR,AT and larger RT,and these conditions are also more conducive to the accumulation of amylose in rice grain.The head rice rate is less affected by light and temperature factors.The results of the AMMI model also show that the head rice rate is mainly influenced by genotype(variety),while the chalkiness,nutritional quality and taste quality are more susceptible to environmental changes.3.Transcriptome analysis of genotypic and environmental responses.The transcriptome data from endosperm at filling stage of Wuyoudao 4,Jijing809 and Tong 35 cultivated in Gongzhuling,Changchun and Wuchang were analyzed.A total of 573 environment-specific differentially expressed genes(DEGs),and 119genotype-specific DEGs were identified;and 11 DEGs were found responsive to genotype-environment interactions.The environment-responsive DEGs are mainly involved in the key metabolic processes such as "cellular carbohydrate metabolism process","photosynthesis,light harvesting",and "regulation of transcriptional " according to GO term enrichment analysis.The GO terms related to “cell death”,“apoptosis”,“transport”,localization”,and “response to stimulus” are significantly enriched in the 119 genotype-responsive DEGs.Among the 11 DEGs responsive to both environment and genotype,there are genes encoding β-precipitase,amino acid permease,cinnamoyl coenzyme a reductase,and cinnamyl alcohol dehydrogenase.4.Characteristics of rice starch particle size distribution and its role in rice grain quality.The distribution range of starch granules diameter of japonica rice tested in this study is about 1.28 μm～51.82 μm.Classified by number,surface area and volume,the average particle size is respectively around 3 μm,4 μm and 5 μm.The distribution curves all showed unimodal distribution,with the peaks around 3 μm,4 μm and 5 μm respectively.The results of the correlation analysis show that rice taste value is significantly positively correlated with the mean values of starch particle size in volume,number and surface area,and the correlation coefficients are 0.64,0.74 and0.69 respectively.That is,small granules of starch tend to lead to poor taste quality,while large granules of starch are beneficial to the improvement of taste quality.5.Protein components and their effects on taste quality in rice grainThe protein content of japonica rice that tested is about 6%,with glutenin(Glu)as the main protein,accounting for about 50% of the total protein content.Prolamin(Pro)is the second largest component of rice protein,which accounts for about 15%of the total protein content,and the content of globulin(glo)is only about 7%.The correlation analysis shows that the taste quality of rice is negatively correlated with protein content,Glu and Pro(correlation coefficients are-0.04,-0.16 and-0.16respectively),while positively correlated with Glo(0.10);however,none of them reached a significant level.6.The role of rice RVA characteristics in the evaluation of rice taste quality.Rice viscosity characteristics are closely related to taste quality.The correlation analysis shows that there is a significantly positive correlation between taste value and peak paste viscosity(PKV),with a correlation coefficient of 0.73.The taste value is also positively correlated with cool paste viscosity(CPV)and breakdown viscosity(BDV),with correlation coefficients of 0.67 and 0.66 respectively;while it was negatively correlated with pasting temperature(Pa T),with a correlation coefficient of-0.90.Consequently,Pa T can be taken as an important index to evaluate the taste quality of rice in the core region for high-quality japonica rice production in Northeast China. |
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