Plant Gene and Trait 2024, Vol.15, No.5, 230-242 http://genbreedpublisher.com/index.php/pgt 231 findings have provided a deeper understanding of the genetic mechanisms underlying these traits and have highlighted the potential for molecular breeding to enhance rice grain yield and quality (Niu et al., 2021; Chen et al., 2021). Recent GWAS have identified key genetic factors influencing rice grain shape and chalkiness, traits critical to quality and market value. Wang et al. (2023) conducted a GWAS on Xian (indica) rice accessions, revealing significant QTLs and candidate genes linked to these traits. These findings provide valuable genetic markers for breeding programs focused on enhancing grain shape and reducing chalkiness, offering a pathway to improve both consumer satisfaction and marketability. A study using the indica rice Multiparent Advanced Generation Intercross (MAGIC) population revealed several key loci associated with grain size traits, such as grain length, width, and thickness. The study conducted by Ponce et al. (2020) employed GWAS and identified significant QTLs, including qGL4 (grain length) and qGW7 (grain width), providing valuable genetic targets for improving grain size and quality in rice breeding programs. Similarly, Gong et al. (2023) discussed elite genes like GS3 and qSW5, which are crucial for improving grain size and quality, and how molecular breeding techniques such as marker-assisted selection (MAS) and genomic selection (GS) have been applied to incorporate these traits into high-quality rice varieties. This review aims to summarize the key genetic factors influencing rice grain shape and palatability; highlight the advancements in genome-wide association studies and their contributions to understanding these traits; identify potential candidate genes and QTLs that could be targeted for future rice breeding programs; and discuss the implications of these findings for improving rice yield and quality through molecular breeding. By providing a comprehensive overview of the genetic determinants of rice grain shape and palatability, we seek to inform and guide future research and breeding efforts aimed at enhancing the quality and marketability of rice. 2 Rice Grain Shape: Genetic and Phenotypic Characteristics 2.1 Definition and assessment of grain shape Rice grain shape is a critical agronomic trait that significantly influences both the yield and quality of rice (Bai et al., 2010). Grain shape is typically defined by several parameters, including grain length (GL), grain width (GW), and grain thickness (GT). These dimensions are used to determine specific grain shape indices, such as the grain length-to-width ratio (L/W), which is often used to classify rice as long, medium, or short-grained. Grain shape plays a crucial role in determining the rice variety's market category and consumer preference, as it affects both cooking properties and aesthetic appeal. These parameters are measured using digital calipers or specialized image analysis software. Advanced phenotyping tools now allow for the high-throughput collection of grain shape data, improving the accuracy of trait analysis in breeding programs. Researchers also employ QTL mapping and GWAS to identify the underlying genetic factors that influence grain shape, aiding in the selection of optimal traits for breeding. (Huang et al., 2013; Niu et al., 2021; Meng et al., 2022). 2.2 Importance of grain shape in consumer preference and market value Grain shape is a major determinant of rice market value and consumer preference. Different markets and cultures have varying preferences for grain shape, which can influence the commercial success of rice varieties. For example, long and slender grains are often preferred in South Asian markets, while shorter and rounder grains may be favored in East Asian markets. Grain shape also significantly affects market value. Longer and slender grains tend to fetch higher prices in international markets due to their appearance and cooking qualities. The aesthetics of rice, including the uniformity of grain shape, contribute to its overall visual appeal and marketability. Studies show that grain shape is often a key criterion in rice grading and pricing (Fitzgerald et al., 2009; Wang et al., 2023). The appearance, processing quality, and palatability of rice are all affected by grain shape, making it a crucial factor in rice breeding programs aimed at meeting consumer demands (Lu et al., 2013; Misra et al., 2018; Angira et al., 2022). 2.3 Genetic determinants of grain shape The genetic basis of rice grain shape is complex and involves multiple genes and QTLs. Advances in genomics have facilitated the identification of numerous QTLs and candidate genes associated with grain shape. Advances
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