| Summary: | Rice is a major crop, providing calories and food for most of the world’s population. Currently, the global population is rapidly increasing, and securing a yield of rice that can satisfy everyone is an ongoing challenge. The yield of rice can be increased by controlling 1000-grain weight as one of the important determining factors. Grain length, grain width, grain thickness, and 1000-grain weight, which determine grain size, are controlled by QTLs. To identify QTLs related to grain size, we screened and then mapped 88 RIL individuals derived from a cross between JJ625LG, which has a long grain size, long spindle-shaped grains, and low 1000-grain weight, and Namchan, which has short grains with round shape and heavy 1000-grain weight. In 2021 and 2022, 511 SNP markers were used to map QTLs related to grain size to a physical map. The QTLs found to be related to grain size are evenly distributed on chromosomes 2, 3, 5, 10, and 11. The mapping results also show that the QTLs <i>qGl3-2</i>, <i>qRlw3</i>, and <i>qRlw3-2</i> of chromosome 3, and qGt5 and <i>qRlw5</i> of chromosome 5 are, respectively, associated with <i>GS3</i> and <i>qSW5</i>, which are the major genes previously cloned and found to be related to grain size. In addition, <i>qGw10</i> and <i>qGw10-1</i>, which were additionally detected in this study, were found to be associated with <i>Os10g0525200</i> (<i>OsCPq10</i>), a potential candidate gene involved in controlling grain size. This gene codes for a cytochrome P450 family protein and is reported to have a positive effect on grain size by interacting with proteins related to mechanisms determining grain size. In particular, <i>OsCPq10</i> was screened in the same identified QTL region for 2 consecutive years, which is expected to have a positive effect on grain size. These results will be helpful for breeding elite rice cultivars with high yields through additional fine mapping related to grain size.
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