**4. Discussion**

The GWAS panel, including released cultivars, advanced lines and landraces from di fferent ecological regions, has a high genetic diversity with a wide range of mesocotyl length. In this study, *Indica* accessions had 32.4% and 70.0% accessions with longer mesocotyls (≥2.0 cm) in sand and 6 cm soil culture, respectively, but only 30.0% and 45.0% accessions in the *Japonica*, indicating that mesocotyl length had a grea<sup>t</sup> potential for improvement. Although mesocotyl is a crucial developmental trait of rice and is imminently required to improve crop adaptability to modern cultivation mode, the molecular mechanisms of its elongation and domestication remains unclear. Here, a GWAS based on re-sequencing were employed to identify associated SNP markers and understand the genetic basis of mesocotyl length.
