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Rice is a staple food for nearly two-thirds of China's population. As socio-economic development continues, there is a growing demand for high-quality rice. This study collected grain quality traits for 17,785 rice varieties approved throughout China, and categorized them into the following five types: indica inbred (II), indica hybrid (IH), japonica inbred (JI), japonica hybrid (JH), and indica-japonica hybrid (IJ). Comprehensive analyses were conducted to assess the differences and trends in rice quality across these varieties. We found that JI and JH excel in processing and cooking qualities, featuring higher brown rice and head milled rice rates, coupling with longer gel consistency. Inbred varieties display lower chalky rice rates than hybrids. Over several decades, head milled rice rates have notably increased across all types except for IJ. Transparency grade has decreased in nearly all types except for IJ, with similar declines observed in chalky rice rates and chalkiness degree, suggesting an overall progress in appearance quality. In terms of cooking and taste attributes, amylose content has decreased in most varieties except for IJ, and gel consistency has improved in indica varieties. Generally, the rice quality of varieties approved in China has shown a clear trend of improvement over the past 40 years. This study provides significant data support and theoretical backing for ongoing rice breeding efforts. [ABSTRACT FROM AUTHOR]

Rice is sensitive to high-temperature stress during almost all stages of growth and development. High-temperature stress has become one of the main factors restricting high yield and superior quality of rice. In this study, recombinant inbred lines (RILs) derived from an indica rice cross between two restorer lines were planted in two years. One sowing date was applied in 2019, and four sowing dates were set in 2020 according to the period of local high temperatures in recent years. Two traits closely related to high-temperature tolerance, heading date (HD), and spikelet fertility (SF) were measured. In each trial, the HD showed a bimodal distribution, whereas SF had a continuous and left-skewed distribution. QTL analysis was performed using a high-density bin map. For HD, a total of six QTL were detected. All of them correspond in position to the cloned genes, among which qHD8 in the DTH8/Ghd8 region showed the largest genetic effect. For SF, a total of eight QTL were detected. Five of them, qSF1, qSF2, qSF3.1, qSF3.2, and qSF8, showed high-temperature tolerance and had an important potential in rice breeding. [ABSTRACT FROM AUTHOR]

High yield and superior quality are the main objectives of rice breeding and research. While innovations in rice breeding have increased production to meet growing demand, the universal issue of balancing high yield and susperior quality has led to a lack of focus on improving rice quality. With rising living standards, improving rice quality has become increasingly important. Rice grain quality is a complex trait influenced by both genetic and environmental factors, with four primary aspects: milling quality, appearance quality, eating and cooking quality, and nutritional quality. While different populations have varying demands for rice quality, the core traits that contribute to rice quality include grain shape and chalkiness in terms of appearance, as well as endosperm composition that influences cooking and sensory evaluation. Researchers have made substantial advancements in discovering genes/QTLs associated with critical traits including appearance, aroma, texture, and nutritional properties. Markers derived from these genetic discoveries have provided an efficient tool for marker-assisted selection to improve rice quality. Thus, this review focuses on elite genes and their applications in breeding practices to quickly develop superior quality rice varieties that meet various market demands. [ABSTRACT FROM AUTHOR]

The source strength and sink demand as well as their interaction have been demonstrated to co-regulate the synthesis of starch and determine the grain quality, but the knowledge of the underlying physiological mechanisms is limiting. An indica variety, Yangdao 6, and a japonica variety, Jinxiangyu 1, were planted with three treatments, including normal growth plant (CK), leaf-cutting (LC) and spikelet-thinning (ST). The transcript levels of starch metabolic genes, physicochemical characteristics of starch and appearance, milling, cooking and tasting qualities of rice under different treatments were determined. The ST treatment increased the relative expression of genes related to the synthesis of short branch-chains of amylopectin (SSI, BEI, BEIIb) and amylose (GBSSI) and reduced the relative expression of medium-long to long branch-chains of amylopectin synthesis genes (SSIIa, SSIIIa, SSIIIb, ISA1). When comparing ST with the CK treatment, starch granules became smoother with higher contents of short branch-chains and lower ratios of medium-long and long branch-chains of amylopectin; the crystallinity and the value of 1045/1022 cm−1 was decreased; for pasting properties, the setback and pasting temperature were decreased; the peak viscosity, hot viscosity, breakdown and final viscosity were significantly increased. Meanwhile, the ST treatment improved the appearance, milling and cooking and tasting qualities. The opposite results were observed under the LC treatment. These results indicated that source strength and sink size would regulate expression levels of starch metabolic genes, which is pivotal for the contents of amylose and short/long branch chains ratio of amylopectin, thus changing the structure and physicochemical properties of starch and grain quality. Here, we speculated that the improved source strength in terms of higher leaf/canopy photosynthesis and small sink size, such as small panicle size, would be preferred traits in high grain quality rice breeding. [ABSTRACT FROM AUTHOR]

For the purpose of breeding documentation, researchers and breeders kept handwritten records of the breeding history, including parental information and breeding methods. The cultivars were used again as parents for further breeding, and modern cultivars of rice have a wide range of alleles from many generations of parents and ancestors. To understand such a breeding history, it is necessary to ask around for relevant information, which is then usually documented in Excel or Word by multiple breeders or breeding institutes. Here, we constructed RicePedigree, which contains the breeding history of rice based on the documents provided by the Rural Development Administration (RDA) in Korea. We devised a simple method for collecting a breeding history and storing it in a database. RicePedigree is a web-based application on the database that facilitates researchers' and breeders' utilization of the breeding history of rice. Based on the query cultivar name, it will return a hierarchical tree of breeding histories and a list of cultivars and breeding lines that contain query cultivars in their breeding histories. This app would be a good way to review and keep track of information about current and future cultivars. [ABSTRACT FROM AUTHOR]

The super hybrid rice breeding program in China has raised genetic yield ceilings through morphological improvements and inter-subspecific heterosis. Despite this, little information on the physiological basis underlying this yield transformation exists, and less so on the genotype x environment x management conditions enabling consistent yield gains. Here, we assess grain yield, photosynthetic physiology, and leaf carbon and nitrogen (N) metabolic properties of super rice (Y-liangyou900) under four management practices (i.e., zero-fertilizer control, CK; farmers' practice, FP; high-yield and high-efficiency management, OPT1; and super-high-yield management, OPT2) using a field experiment conducted over five years. Grain yield and agronomic N use efficiency (AEN) of OPT2 were 15% and 10% higher than OPT1, and 30% and 78% higher than FP, respectively. The superior yields of OPT2 were attributed to higher source production capacity, that is, higher leaf photosynthetic rate, carbon metabolic enzyme activity (i.e., AGP and SPS), nitrogen metabolic enzyme activity (i.e., NR, GS, and GOGAT), soluble protein and sugar content, and delayed leaf senescence (the latter due to elevated activity of protective enzyme systems) during grain filling. The higher AEN of OPT2 was associated with higher activity of leaf carbon metabolic enzyme (i.e., AGP and SPS), nitrogen metabolic enzyme (i.e., NR, GS, GDH, and GOGAT) and protective enzyme (POD) after heading, and lower C/N ratio in grains. We conclude that optimized management (optimized water and fertilizer management with appropriate dense planting) improved grain yield and N use efficiency simultaneously by enhancing post-heading leaf carbon and N metabolism and delayed leaf senescence. [ABSTRACT FROM AUTHOR]

Brown planthopper, blast, and bacterial blight are the main biotic stressors of rice and can cause a massive loss in rice production. Aroma is an important character of rice quality. It is of far-reaching significance to breed resistant and high-quality varieties using germplasms with objective genes. In this study, the introgression and pyramiding of brown planthopper (BPH), blast, and bacterial leaf blight (BLB) resistance genes and aroma genes into elite rice maintainers and restorers were conducted through conventional cross-breeding coupled with the marker-assisted selection (MAS) breeding method. Single-plant selection was performed from F2 onwards to select desirable recombinants possessing alleles of interest with suitable phenotypes. Respective linked markers were used in each generation from intercrossing to the F7 generation for tracking the presence of targeted genes. A total of 74 improved lines (ILs) have been developed which possess a combination of 1 to 4 genes for BPH, blast, and BLB resistance and aroma. These ILs showed moderate to high resistance to multiple biotic stresses (BPH, blast and BLB) or aromatic fragrance without obvious negative effects on agronomic traits. As multiple resistance and aromatic traits have become significant objectives in rice breeding, these resistance and/or aroma gene introgressed or pyramided lines have important application prospects. Core ideas: (1) marker-assisted breeding was used to pyramid multiple genes for an elite breeding line; (2) improved lines with the introgression of 1–4 genes were developed to achieve high resistance against various biotic stresses and aroma; (3) new lines were used as donor parents to introgress multiple genes in other genetic backgrounds. [ABSTRACT FROM AUTHOR]

The japonica rice in Northeast China is famous because of its high quality. Eating and cooking qualities (ECQs) are the most important factors that determine cooked rice quality. However, the genetic basis of ECQ of japonica varieties in Northeast China needs further study. In this study, 200 japonica varieties that are widely distributed in Northeast China were collected to evaluate the physicochemical indices of grain ECQs. The distribution of each trait was concentrated without large variations. Correlation analysis indicated that gel consistency (GC) had a significantly negative correlation with gelatinization temperature (GT). By integrating various analyses including kinship calculation, principal component analysis (PCA), linkage disequilibrium (LD) analysis, and original parent investigation, we found that the japonica varieties in Northeast China exhibited a narrow genetic basis. An association study for grain ECQs was performed and eight quantitative trait loci (QTLs) were detected. ALK was the major locus that regulated GT and also significantly affecting GC. Through the linkage disequilibrium (LD) and expression pattern analysis, one possible candidate gene (LOC_Os02g29980) was predicted and required further research for validation. Additionally, a different allele of Wx was identified in the variety CH4126, and ALK was not fixed in these japonica varieties. These results further elucidate the genetic basis of ECQs of japonica varieties in Northeast China and provide local breeders some assistance for improving ECQs of rice grain in rice breeding. [ABSTRACT FROM AUTHOR]