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Grain quality has become one of the foci in rice breeding worldwide since it is crucial for farmers, millers and consumers. Previous studies have revealed that rice gain quality is mainly determined with several major characteristics including milling, physical appearance, eating and cooking, sensory and nutritional value. In genetics, rice grain quality is a complex trait controlled by polygene/QTL. Better understanding the mechanism underlying the grain quality is fundamental for developing new breeding strategies. Therefore, abundant studies had been conducted to discover the factors that control the quality traits, and led to dozens of QTL identified and several major genes cloned. This has enabled development of the functional markers to facilitate selection of the complex traits. But breeding for rice varieties with desired grain quality needs to pyramid multiple and beneficial loci or alleles, some of which are still untapped. In this chapter, we first summarize the literatures on rice grain quality traits and the relevant phenotyping approaches, and then review the progress in genetic dissection of these traits. This review also presented the breeding attempts using marker-assisted selection, genomics-assisted breeding approaches, as well as genome editing technologies, and finally provided innovative insights into the future of rice grain quality breeding by using the modern technology with integration of machine learning and genomic selection. [ABSTRACT FROM AUTHOR]

Waxy (Wx) gene in rice endosperm synthesizes amylose and amylopectin extra-long chain (ELC). Five rice lines with different Wx locus single-segment substitutions under the same genetic background were investigated for relationships of their starch molecular components and eating and cooking qualities (ECQs) including pasting, thermal, textural and sensory properties. Rice lines with different Wx loci exhibited different ECQs, and their starches had different apparent amylose contents (AACs), true amylose contents (TACs), ELC contents (ELCCs), and amylopectin chain length distributions. The AAC was correlated positively to hardness and cohesiveness of cooked rice, and negatively to adhesiveness and palatability of cooked rice and breakdown viscosity of rice flour. The TAC was correlated positively to gelatinization temperature range and negatively to gelatinization temperature and enthalpy. ELCC showed a positive relationship with pasting peak time of rice flour and chewiness of cooked rice, and could potentially be used as an important reference for rice ECQ evaluation. This study could help the applications of Wx loci in rice quality breeding. [Display omitted] • Rice Wx locus single-segment substitution lines had the same genetic background. • AAC was related positively to hardness and negatively to palatability of cooked rice. • TAC was negatively related to gelatinization temperature and enthalpy of rice flour. • ELCC was positively related to P Time of rice flour and chewiness of cooked rice. • Amylopectin branch-chains had significant relationship with some ECQ parameters. [ABSTRACT FROM AUTHOR]

Grain qualities including milling quality, appearance quality, eating and cooking quality, and nutritional quality are important indicators in rice breeding. Significant achievements in genetic improvement of rice quality have been made. In this study, we analyzed the variation patterns of 16 traits in 1570 rice varieties and found significant improvements in appearance quality and eating and cooking quality, particularly in hybrid rice. Through genome-wide association study and allelic functional nucleotide polymorphisms analysis of quality trait genes, we found that ALK , FGR1 , FLO7 , GL7 / GW7 , GLW7 , GS2 , GS3 , ONAC129 , OsGRF8 , POW1 , WCR1 , and Wx were associated with the genetic improvement of rice quality traits in Southern China. Allelic functional nucleotide polymorphisms analysis of 13 important rice quality genes, including fragrance gene fgr , were performed using the polymerase chain reaction amplification refractory mutation system technology. The results showed that Gui516, Gui569, Gui721, Ryousi, Rsimiao, Rbasi, and Yuehui9802 possessed multiple superior alleles. This study elucidates the phenotypic changes and molecular basis of key quality traits of varieties in Southern China. The findings will provide guidance for genetic improvement of rice quality and the development of new varieties. • Appearance quality (AQ) and eating and cooking quality (ECQ) • ALK , FGR1 , FLO7 , GL7 / GW7 , GLW7 , GS2 , GS3 , ONAC129 , OsGRF8 , POW1 , WCR1 , and Wx are the main genes affecting rice quality in Southern China. • Gui516, Gui569, Gui721, Ryousi, Rsimiao, Rbasi, and Yuehui9802 possessed multiple superior alleles of rice quality. [ABSTRACT FROM AUTHOR]

Rice, the most consumed in Asian and constitute important source of amino acids. The present study evaluated the suitability of near-infrared reflectance spectroscopy to predict amino acid contents (AACs) using 1210 rice samples representing a wide range of grain qualities and genetic background. Calibration models established by combining different spectral derivatives, scatter and baseline correction methods, and regression algorithm were compared using full cross validation. A modified partial least square model (MPLS) with the spectral derivative treatment "2, 3, 3, 1" (2nd order derivative computed based on 3 data points, and 3 and 1 data points in the 1st and 2nd smoothing, respectively) and weighted multiplicative scattering correction (WMSC) method was identified as the best model for simultaneously measurement of 14 AACs in brown rice flour. The high model quality is reflected by RSQ of 0.914∼0.969, standard error of calibration (SEC) of 0.0187%∼0.0553%, 1-VR of 0.901∼0.955, SECV of 0.0214%∼0.0579%, and residual prediction deviation (RPD) of 2.58∼3.85. These results indicated that NIRS coupled with an appropriate pre-processing, multivariate regression could be a rapid and reliable method for quantification of AACs in rice breeding programs and quality control in the food industry. Factors that would influence model quality were investigated and discussed. • NIRS is capable of accurately quantifying 14 amino acids contents in diverse rice samples. • MPLS was the most robust regression method. • MSC and 2nd derivation were suitable pre-processing methods. • NIRS is applicable for high-throughput screening. [ABSTRACT FROM AUTHOR]

High-quality rice varieties are planted widely in southern China. However, the changes in grain quality in the different high-quality rice varieties released in recent years are unclear. This study compared the grain quality changes and status of those varieties and presented proposals for future breeding. In the past 11 years, high-quality indica has significantly improved chalky rice rate (CRR), chalkiness degree (CD) but decreased head rice rate (HRR); amylose content (AC), gel consistency (GC) and length-to-width ratio (LWR) were improved only in indica hybrid rice. Most high-quality rice varieties grown in southern China are primarily indica rice. In contrast to indica rice, japonica rice had increased milling recovery, cooking and eating qualities (CEQ), but worsened significantly the physical appearance. For japonica rice, hybrid varieties exhibited a marked improvement in the rice quality for lower AC, higher GC and LWR compared with inbred varieties. A higher grain quality was observed in inbred varieties for indica rice due to lower CRR, CD and AC, higher HRR and GC. Our results suggested that we should be focused on improving the physical appearance quality for japonica rice and milling recovery, particularly CEQ for indica rice, for future high-quality rice breeding. • High-quality indica rice has significantly improved chalky rice rate and degree of chalkiness over time. • High-quality japonica rice had increased milling recovery and CEQ compared with high-quality indica rice. • High-quality japonica hybrid rice significantly improved grain quality and that was observed in indica inbred rice. [ABSTRACT FROM AUTHOR]

The objective of this work was to define a quality space for assessing rice varieties. Eleven long grain varieties, seven commercial and four new advanced lines were assessed to obtain complete quality profile considering appearance, physicochemical parameters, water absorption behaviour, pasting profile and textural attributes. Commercial varieties were chosen to provide the widest variation in properties, applying the variability analysis concepts of the Taguchi method, including Japonicas , Indicas , hybrids and aromatics. Quality parameters were measured in five different dimensions of quality space (totalling 50). Variable reduction techniques were applied to chose 3 parameters in each dimension (totalling 15 quality indicators) that would describe the whole space with greatest orthogonality, accuracy and yet explaining a significant proportion of the whole variance of data. The analysis of the quality space thus defined and similarities between varieties is illustrated with the conclusion of how the 4 new advanced lines perform in terms of quality behaviour, where it is concluded that one of them is very promising as an improvement over European ( Indica ) towards the behaviour of a pure Guyana ( Indica ), whereas 3 others have significant shortcomings in various aspects of the quality space compared to all others, albeit their greater closeness to Japonicas . [ABSTRACT FROM AUTHOR]

Starch components determine rice quality and utilization. Rice floury endosperm grains have poor quality. In this study, we screened 27 non-floury endosperm mutants with different starch components from a mutant population derived from japonica rice variety Nipponbare using urea gelatinizing grain-iodine staining method. Nine mutants of MY03, MY12, MY16, MA06, MA15, MP09, MP20, MP31 and MP40 were chosen for identification of homozygous mutant and analysis of starch components and grain properties. The amylose content in single grain indicated that the screened mutants were homozygous and the stained solution color of gelatinized grain could reflect the starch components of brown rice grain. The MY03, MY12 and MY16 grains had altered amylopectin structures and exhibited high gelatinization temperatures and strong resistances to urea gelatinization. Compared with Nipponbare grains, MA06 and MA15 grains had very high amylose and lipid contents. The MP09, MP20, MP31 and MP40 grains had significantly lower amylose contents than Nipponbare grains. The screened mutants had similar grain transparency to Nipponbare. This study provided a method reference for rapidly screening rice non-floury endosperm mutants from thousands of mutant lines, and the screened mutants were important genetic materials for revealing starch synthesis and regulation and good germplasm resources for rice quality breeding. [Display omitted] • Rice mutants were screened using urea gelatinizing grain-iodine staining method. • Non-floury endosperm mutants with different starch components were screened. • The amylose content in single grain confirmed the screened grain homozygous mutation. • Mutant grains exhibited low amylose, high amylose and lipids, or altered amylopectin. • Mature grain transparency was similar between mutant and wild type rice Nipponbare. [ABSTRACT FROM AUTHOR]

An extreme high temperature during grain filling is an important environmental factor that reduce the yield and quality of rice. In this study, we compared the grain appearance, composition and starch structure of four rice varieties response to high temperature during grain filling. The results obviously revealed that two indica AUS varieties Halwa and Jamir showed more tolerance to high temperature during grain filling than either the japonica Nipponbare or another AUS rice DJ24. The data showed that Halwa and Jamir presented less chalkiness, less grain weight loss, less change of endosperm components as well as starch structure than Nipponbare and DJ24 under high temperature treatment. Hence, the results implied that Halwa and Jamir might be useful targets to further identify genetic mechanism response to high temperature, at least during grain filling and endosperm development. Moreover, these AUS varieties have potential application value in further breeding of rice with good quality and heat tolerance. Image 1 • Jamir and Halwa are two AUS rice varieties that originated from low latitudes. • The yield and quality characteristics of Jamir and Halwa were hardly affected by high temperature. • The influences of high temperature on the starch fine structure of Jamir and Halwa were much slighter. [ABSTRACT FROM AUTHOR]