Plant Gene and Trait 2024, Vol.15, No.5, 230-242 http://genbreedpublisher.com/index.php/pgt 236 utilized a high-density genetic map with 3 203 Bin markers to detect 91 QTLs for grain shape, with 64 forming 15 clusters, and three new QTLs identified (Kang et al., 2021). These comparative studies highlight the genetic diversity and stability of palatability traits across different genetic backgrounds and environmental conditions. 7 Integrative Analysis of Grain Shape and Palatability 7.1 Correlation between grain shape and palatability Grain shape is a critical determinant of rice quality, influencing both yield and consumer preferences. Traits such as grain length, width, and roundness are closely associated with sensory properties like softness, stickiness, and overall mouthfeel (Huang et al., 2013). Long, slender grains tend to be less sticky and firmer after cooking, which may appeal to consumers in regions where rice is served as individual grains. Conversely, shorter, rounder grains are often associated with softer textures and higher stickiness, characteristics that contribute to the palatability preferred in other cultural contexts (Misra et al., 2018). Studies have shown that grain shape, including traits such as GL, GW, and length-width ratio (LWR), significantly impacts the palatability of rice. The identification of QTLs associated with grain shape in high-yielding rice varieties has provided insights into the genetic factors that contribute to both yield and quality (Kang et al., 2020; Kang et al., 2021; Meng et al., 2022). Moreover, the grain shape impacts the water absorption rate during cooking, which directly affects the final texture and taste of the rice (Feng et al., 2016). The correlation between grain shape and palatability is further supported by the discovery of pleiotropic effects of certain QTLs, which affect multiple traits including grain shape and eating quality (Ogawa et al., 2018; Wang et al., 2023). This suggests that breeding programs targeting grain shape improvements can simultaneously enhance rice palatability. 7.2 Combined GWAS and QTL studies The integration of GWAS and QTL mapping has proven to be a powerful approach to identifying genetic determinants of grain shape. The use of a combined linkage mapping and GWAS strategy has led to the identification of several QTLs that govern rice grain shape and weight, with significant contributions to phenotypic variation (Kang et al., 2020). Similarly, haplotype-based GWAS has been effective in evaluating multiple QTLs with small effects on grain shape, providing high-accuracy QTL detection (Ogawa et al., 2018). These integrative studies have not only identified novel QTLs but also validated known ones, thereby enhancing our understanding of the genetic architecture of grain shape (Niu et al., 2020; Kabange et al., 2023; Wang et al., 2023). For example, studies by Misra et al. (2018) and Yano et al. (2016) employed combined GWAS and QTL strategies, identifying key loci such as GS3, GW5, and qGL3 that regulate grain length and width. Additionally, Chen et al. (2016) highlighted the use of integrative mapping for discovering pleiotropic QTLs influencing both grain shape and chalkiness. These insights pave the way for more precise marker-assisted selection in rice breeding programs, improving grain quality and yield. 7.3 Case studies of successful breeding programs Several breeding programs have successfully utilized the findings from GWAS and QTL studies to develop rice varieties with improved grain shape and palatability. The identification of major QTL clusters and candidate genes has facilitated the breeding of high-yielding rice varieties with desirable grain shapes (Chen et al., 2021; Kang et al., 2021). In Japan, the JAM population has been used to identify QTLs for grain shape, leading to the development of rice lines with optimized grain traits for better eating quality (Figure 3) (Ogawa et al., 2018). Additionally, the validation of QTLs in different populations and environments has provided robust genetic markers for marker-assisted selection (MAS), enabling the production of rice varieties with consistent quality and yield (Zhou et al., 2019). Ashikari and Matsuoka (2006) highlighted the successful application of QTL pyramiding in rice breeding, focusing on combining multiple QTLs to enhance grain shape, yield, and other agronomic traits. Their work demonstrated how integrating various QTLs related to grain size and quality can lead to the development of superior rice varieties. These case studies highlight the practical applications of genetic research in rice breeding programs aimed at enhancing both grain shape and palatability.
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