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This review mainly focuses on the rice grain quality based on which rice varieties are distinguished into several quality classes like, physical quality, eating and cooking quality and nutritional quality. The rice breeding programme needs to focus on the development of nutrient-dense rice for value addition, helping in reducing malnutrition and Vitamin-A deficiency (VAD). There is enough scope to enhance the nutritional and cooking quality in small and medium grain rice germplasm by bringing them into the breeding programme through Fe and Zn and Vitamin-A biofortification, aided with molecular techniques. Many studies have been conducted to find out the quantitative trait locus (QTL) for enhancing the quality of grain. The QTL qBRR5 and qBRR3 are responsible for brown rice grain width and length found on chromosome 5 and on chromosome number 3, respectively and for head rice on chromosome number 1, 5, and 6. The QTLs present on chromosomes 3, 5, and 6 are responsible for head rice recovery, chalky appearance of rice grain as well as grain size and shape. The gene Wx, located on chromosome 6 linked with the QTL qAC6 regulate amylose content and gel consistency. The QTL SSIIa on chromosome 6, control both the amylopectin and gelatinization temperature. The QTLs for Fe and Zn content in rice grain are located on chromosome 2, 3, 8, 11 and 12. Development of “Golden rice” and innovations with Arabidopsis genes can significantly enhance β-carotene levels and address Vitamin-A deficiency, while RNAi techniques improve storage quality. [ABSTRACT FROM AUTHOR]

Summary: Head rice yield (HRY) measures rice milling quality and determines final grain yield and commercial value. Here, we report that two major quantitative trait loci for milling quality in rice, qMq‐1 and qMq‐2, represent allelic variants of Waxylv/Waxyb (hereafter Wx) encoding Granule‐Bound Starch Synthase I (GBSSI) and Alkali Spreading Value ALKc/ALKb encoding Soluble Starch Synthase IIa (SSIIa), respectively. Complementation and overexpression transgenic lines in indica and japonica backgrounds confirmed that Wx and ALK coordinately regulate HRY by affecting amylose content, the number of amylopectin branches, amyloplast size, and thus grain filling and hardness. The transcription factor OsDOF18 acts upstream of Wx and ALK by activating their transcription. Furthermore, rice accessions with Wxb and ALKb alleles showed improved HRY over those with Wxlv and ALKc. Our study not only reveals the novel molecular mechanism underlying the formation of HRY but also provides a strategy for breeding rice cultivars with improved HRY. [ABSTRACT FROM AUTHOR]

Grain size is a quantitative trait with a complex genetic mechanism, characterized by the combination of grain length (GL), grain width (GW), length to width ration (LWR), and grain thickness (GT). In this study, we conducted quantitative trait loci (QTL) analysis to investigate the genetic basis of grain size using BC1F2 and BC1F2:3 populations derived from two indica lines, Guangzhan 63-4S (GZ63-4S) and TGMS29 (core germplasm number W240). A total of twenty-four QTLs for grain size were identified, among which, three QTLs (qGW1, qGW7, and qGW12) controlling GL and two QTLs (qGW5 and qGL9) controlling GW were validated and subsequently fine mapped to regions ranging from 128 kb to 624 kb. Scanning electron microscopic (SEM) analysis and expression analysis revealed that qGW7 influences cell expansion, while qGL9 affects cell division. Conversely, qGW1, qGW5, and qGW12 promoted both cell division and expansion. Furthermore, negative correlations were observed between grain yield and quality for both qGW7 and qGW12. Nevertheless, qGW5 exhibited the potential to enhance quality without compromising yield. Importantly, we identified two promising QTLs, qGW1 and qGL9, which simultaneously improved both grain yield and quality. In summary, our results laid the foundation for cloning these five QTLs and provided valuable resources for breeding rice varieties with high yield and superior quality. [ABSTRACT FROM AUTHOR]

The quality of rice (Oryza sativa L) is determined by a combination of appearance, flavor, aroma, texture, storage characteristics, and nutritional composition. Rice quality directly influences acceptance by consumers and commercial value. The genetic mechanism underlying rice quality is highly complex, and is influenced by genotype, environment, and chemical factors such as starch type, protein content, and amino acid composition. Minor variations in these chemical components may lead to substantial differences in rice quality. Among these components, starch is the most crucial and influential factor in determining rice quality. In this study, quantitative trait loci (QTLs) associated with eight physicochemical properties related to the rapid viscosity analysis (RVA) profile were identified using a high-density sequence map constructed using recombinant inbred lines (RILs). Fifty-nine QTLs were identified across three environments, among which qGT6.4 was a novel locus co-located across all three environments. By integrating RNA-seq data, we identified the differentially expressed candidate gene OsCRLK2 within the qGT6.4 interval. osclrk2 mutants exhibited decreased gelatinization temperature (GT), apparent amylose content (AAC) and viscosity, and increased chalkiness. Furthermore, osclrk2 mutants exhibited downregulated expression of the majority of starch biosynthesis-related genes compared to wild type (WT) plants. In summary, OsCRLK2, which encodes a receptor-like protein kinase, appears to consistently influence rice quality across different environments. This discovery provides a new genetic resource for use in the molecular breeding of rice cultivars with improved quality. [ABSTRACT FROM AUTHOR]

Heading date is a critical agronomic trait that significantly affects grain yield and quality in rice. As early heading is typically associated with reduced yield due to shorter growth duration, it is essential to harness optimum heading date genes and their allelic combinations to promote heading while minimizing yield penalties. In this study, we identified quantitative trait loci (QTLs) for heading date and other major agronomic traits in a recombinant inbred line (RIL) population derived from a cross between Koshihikari and Baegilmi. Analyses on 3 major QTLs for heading date and their underlying genes (Hd1 , Hd16 , and Ghd7) revealed their pleiotropic effects on culm length, panicle length, and head rice percentage. Additionally, Ghd7 exhibited pleiotropic effects on panicle number and grain size. Among 8 different types of allelic combinations of the 3 heading date genes, RILs carrying a single nonfunctional hd16 or ghd7 under the functional background of the other 2 genes (Hd1hd16Ghd7 and Hd1Hd16ghd7) showed potential for maintaining yield and quality-related traits while accelerating heading. These results provide valuable insights for fine-tuning heading dates in rice breeding programs. [ABSTRACT FROM AUTHOR]

Improving quality is an essential goal of rice breeding and production. However, rice quality is not solely determined by genotype, but is also influenced by the environment. Phenotype plasticity refers to the ability of a given genotype to produce different phenotypes under different environmental conditions, which can be a representation of the stability of traits. Seven quality traits of 141 hybrid combinations, deriving from the test-crossing of 7 thermosensitive genic male sterile (TGMS) and 25 restorer lines, were evaluated at 5 trial sites with intermittent sowing of three to five in Southern China. In the Yangtze River Basin, it was observed that delaying the sowing time of hybrid rice combinations leads to an improvement in their overall quality. Twelve parents were identified to have lower plasticity general combing ability (GCA) values with increased ability to produce hybrids with a more stable quality. The parents with superior quality tend to exhibit lower GCA values for plasticity. The genome-wide association study (GWAS) identified 13 and 15 quantitative trait loci (QTLs) associated with phenotype plasticity and BLUP measurement, respectively. Notably, seven QTLs simultaneously affected both phenotype plasticity and BLUP measurement. Two cloned rice quality genes, ALK and GL7, may be involved in controlling the plasticity of quality traits in hybrid rice. The direction of the genetic effect of the QTL6 (ALK) on alkali spreading value (ASV) plasticity varies in different cropping environments. This study provides novel insights into the dynamic genetic basis of quality traits in response to different cropping regions, cultivation practices, and changing climates. These findings establish a foundation for precise breeding and production of stable and high-quality rice. [ABSTRACT FROM AUTHOR]

Improving rice yield is one of the most important food issues internationally. It is an undeniable goal of rice breeding, and the effective panicle number (EPN) is a key factor determining rice yield. Increasing the EPN in rice is a major way to increase rice yield. Currently, the main quantitative trait locus (QTL) for EPN in rice is limited, and there is also limited research on the gene for EPN in rice. Therefore, the excavation and analysis of major genes related to EPN in rice is of great significance for molecular breeding and yield improvement. This study used japonica rice varieties Dongfu 114 and Longyang 11 to construct an F5 population consisting of 309 individual plants. Two extreme phenotypic pools were constructed by identifying the EPN of the population, and QTL-seq analysis was performed to obtain three main effective QTL intervals for EPN. This analysis also helped to screen out 34 candidate genes. Then, EPN time expression pattern analysis was performed on these 34 genes to screen out six candidate genes with higher expression levels. Using a 3K database to perform haplotype analysis on these six genes, we selected haplotypes with significant differences in EPN. Finally, five candidate genes related to EPN were obtained. [ABSTRACT FROM AUTHOR]

Panicle length (PL) is an important trait that determines panicle architecture and strongly affects grain yield and quality in rice. However, this trait has not been well characterized genetically, and its contribution to yield improvement is not well understood. Characterization of novel genes related to PL is of great significance for breeding high-yielding rice varieties. In our previous research, we identified qPL5, a quantitative trait locus for PL. In this study, we aimed to determine the exact position of qPL5 in the rice genome and identify the candidate gene. Through substitution mapping, we mapped qPL5 to a region of 21.86 kb flanked by the molecular marker loci STS5-99 and STS5-106 in which two candidate genes were predicted. By sequence analysis and relative expression analysis, LOC-Os05g41230, which putatively encodes a BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 precursor, was considered to be the most likely candidate gene for qPL5. In addition, we successfully developed a pair of near-isogenic lines (NILs) for qPL5 in different genetic backgrounds to evaluate the genetic effects of qPL5. Agronomic trait analysis of the NILs indicated that qPL5 positively contributes to plant height, grain number per panicle, panicle length, grain yield per plant, and flag leaf length, but it had no influence on heading date and grain-size-related traits. Therefore, qPL5 and the markers tightly linked to it should be available for molecular breeding of high-yielding varieties. [ABSTRACT FROM AUTHOR]

Grain weight is a key trait that determines rice quality and yield, and it is primarily controlled by quantitative trait loci (QTL). Recently, attention has been paid to minor QTLs. A minor effect QTL qTGW7 that controls grain weight was previously identified in a set of chromosomal fragment substitution lines (CSSLs) derived from Nipponbare (NPB)/93-11. Compared to NPB, the single segment substitution line (SSSL) N83 carrying the qTGW7 introgression exhibited an increase in grain length and width and a 4.5% increase in grain weight. Meanwhile, N83 was backcrossed to NPB to create a separating population, qTGW7b, a QTL distinct from qTGW7, which was detected between markers G31 and G32. Twelve near-isogenic lines (NILs) from the BC9F3 population and progeny of five NILs from the BC9F3:4 population were genotyped and phenotyped, resulting in the fine mapping of the minor effect QTL qTGW7b to the approximately 86.2-kb region between markers G72 and G32. Further sequence comparisons and expression analysis confirmed that five genes, including Os07g39370, Os07g39430, Os07g39440, Os07g39450, and Os07g39480, were considered as the candidate genes underlying qTGW7b. These results provide a crucial foundation for further cloning of qTGW7b and molecular breeding design in rice. [ABSTRACT FROM AUTHOR]

Significant achievements have been made in breeding programs for the heavy‐panicle‐type (HPT) rice (Oryza sativa) in Southwest China. The HPT varieties now exhibit excellent lodging resistance, allowing them to overcome the greater pressures caused by heavy panicles. However, the genetic mechanism of this lodging resistance remains elusive. Here, we isolated a major quantitative trait locus, Panicle Neck Diameter 1 (PND1), and identified the causal gene as GRAIN NUMBER 1A/CYTOKININ OXIDASE 2 (Gn1A/OsCKX2). The null gn1a allele from rice line R498 (gn1aR498) improved lodging resistance through increasing the culm diameter and promoting crown root development. Loss‐of‐function of Gn1a/OsCKX2 led to cytokinin accumulation in the crown root tip and accelerated the development of adventitious roots. Gene pyramiding between the null gn1aR498 allele with two gain‐of‐function alleles, STRONG CULM 2 (SCM2) and SCM3, further improved lodging resistance. Moreover, Gn1a/OsCKX2 had minimal influence on overall rice quality. Our research thus highlights the distinct genetic components of lodging resistance of HPT varieties and provides a strategy for tailor‐made crop improvement of both yield and lodging resistance in rice. [ABSTRACT FROM AUTHOR]

The determination of rice grain quality (RGQ) parameters is important because it is the benchmark of rice breeding success to meet up the consumers' demand. RGQ includes milling, storage, cooking, eating, nutrition, and market quality of rice grain. Furthermore, demand for high-quality rice has increased globally and is expected to continue to rise due to consumer preferences. However, global consumer demand, culture, and demographic variances determine acceptable RGQ attributes. For example, European consumers prefer long-grain, nonaromatic rice, whereas Middle Eastern consumers prefer long-grain, well-milled rice with a strong aroma. To improve the rice quality, RGQ analysis is the best way; besides we need to understand the genetic mechanism of the several grain quality quantitative trait loci (QTLs) actions. A better understanding of these QTLs can be tremendously useful in the development of novel RGQ varieties. This review is intended to study major RGQ parameters and their assessment tools. This study is focusing on the limitations and prospects of QTLs to improve RGQ. [ABSTRACT FROM AUTHOR]

Chalkiness is one of the key determinants of rice quality and is a highly undesirable trait for breeding and marketing. In this study, qWCR7, a major quantitative trait locus (QTL) of white-core rate (WCR), was genetically validated using a BC3F2 segregation population and further fine mapped using a near isogenic line (NIL) population, of which both were derived from a cross between the donor parent DL208 and the recurrent parent ZS97. qWCR7 was finally narrowed to a genomic interval of ~ 68 kb, containing seven annotated genes. Among those, two genes displayed markedly different expression levels in endosperm of NILs. Transcriptome analysis showed that the synthesis and accumulation of metabolites played a key role in chalkiness formation. The contents of storage components and expression levels of related genes were detected, suggesting that starch and storage protein were closely related to white-core trait. Our findings have laid the foundation of map-based cloning of qWCR7, which may have potential value in quality improvement during rice breeding. [ABSTRACT FROM AUTHOR]

Background: Improving the overall production of rice with high quality is a major target of breeders. Mining potential yield-related loci have been geared towards developing efficient rice breeding strategies. In this study, one single-locus genome-wide association studies (SL-GWAS) method (MLM) in conjunction with five multi-locus genome-wide association studies (ML-GWAS) approaches (mrMLM, FASTmrMLM, pLARmEB, pKWmEB, and ISIS EM-BLASSO) were conducted in a panel consisting of 529 rice core varieties with 607,201 SNPs. Results: A total of 152, 106, 12, 111, and 64 SNPs were detected by the MLM model associated with the five yield-related traits, namely grain length (GL), grain width (GW), grain thickness (GT), thousand-grain weight (TGW), and yield per plant (YPP), respectively. Furthermore, 74 significant quantitative trait nucleotides (QTNs) were presented across at least two ML-GWAS methods to be associated with the above five traits successively. Finally, 20 common QTNs were simultaneously discovered by both SL-GWAS and ML-GWAS methods. Based on genome annotation, gene expression analysis, and previous studies, two candidate key genes (LOC_Os09g02830 and LOC_Os07g31450) were characterized to affect GW and TGW, separately. Conclusions: These outcomes will provide an indication for breeding high-yielding rice varieties in the immediate future. [ABSTRACT FROM AUTHOR]

Background: Seed dormancy, a quality characteristic that plays a role in seed germination, seedling establishment and grain yield, is affected by multiple genes and environmental factors. The genetic and molecular mechanisms underlying seed dormancy in rice remain largely unknown. Results: Quantitative trait loci (QTLs) for seed dormancy were identified in two different mapping populations, a chromosome segment substitution line (CSSL) and backcross inbred line (BIL) population, both derived from the same parents Nipponbare, a japonica cultivar with seed dormancy, and 9311, an indica cultivar lacking seed dormancy. A total of 12 and 27 QTL regions for seed dormancy were detected in the CSSLs and BILs, respectively. Among these regions, four major loci (qSD3.1, qSD3.2, qSD5.2 and qSD11.2) were commonly identified for multiple germination parameters associated with seed dormancy in both populations, with Nipponbare alleles delaying the seed germination percentage and decreasing germination uniformity. Two loci (qSD3.1 and qSD3.2) were individually validated in the near-isogenic lines containing the QTL of interest. The effect of qSD3.2 was further confirmed in a CSSL-derived F2 population. Furthermore, both qSD3.1 and qSD3.2 were sensitive to abscisic acid and exhibited a significant epistatic interaction to increase seed dormancy. Conclusions: Our results indicate that the integration of the developed CSSLs and BILs with high-density markers can provide a powerful tool for dissecting the genetic basis of seed dormancy in rice. Our findings regarding the major loci and their interactions with several promising candidate genes that are induced by abscisic acid and specifically expressed in the seeds will facilitate further gene discovery and a better understanding of the genetic and molecular mechanisms of seed dormancy for improving seed quality in rice breeding programs. [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]