Fine-Mapping of a Major Quantitative Trait Locus q2ID1 for Rice Stem Diameter

Rice culm is an important trait for determining rice lodging yield, and stem diameter has been suggested as a yield-related trait; however, studies for the genetic basis of its phenotypic variation are still required. In this study, we used 160 recombination inbred lines derived from a cross of two different rice varieties [‘Milyang23’ (Tongil rice) and ‘Giho’ (japonica)] for quantitative trait locus (QTL) mapping with nine stem traits. The analysis showed that QTLs for the diameters of the first, second, third and fourth internode traits were independently separated in the top of chromosome 1, whereas four lengths of internodes were estimated as being related to the semidwarf1 (sd1) gene. A major-effect QTL (q2ID1) was identified that the overlapped region of our previous mapping with a large genomic region. Therefore, we performed high-resolution genetic mapping for fine-mapping of q2ID1 to a ~140 kb region between Ind1_1 and Ind1_2 of genetic markers, with candidate genes predicted using a reference genome. We ultimately identified nine of the 15 candidate genes with specific gene functions and analyzed the sequence variations between two parents. These results offer valuable gene and/or genetic information on stem diameter to improve lodging resistance and yield.