Red pericarp trait, common to weedy rice, contributes to freezing tolerance of seeds and their ability to overwinter in soil

The red pericarp trait is controlled by <i>Rc</i> and <i>Rd</i>, is prevalent in weedy rice, and is associated with seed dormancy and longevity. However, the individual and combined effects of these genes on seed adaptation remain unclear. We developed near-isogenic lines (NILs) carrying 'Kasalath' <i>Rc</i> and/or <i>Rd</i> alleles in the 'Koshihikari' background and evaluated seed dormancy, freezing tolerance, and overwintering ability under controlled and field conditions, using 'Koshihikari', 'Kasalath', and the Japanese weedy rice accession 'JP_1177' as controls. NILs carrying <i>Rc</i>, <i>Rd</i>, or both did not have the deep primary dormancy typical of weedy rice. Under field conditions, these lines germinated prematurely and failed to survive winter, unlike 'JP_1177'. However, the NIL carrying both <i>Rc</i> and <i>Rd</i> had higher freezing tolerance than the other lines, suggesting an interaction between these genes. These findings indicate that the red pericarp trait does not confer deep dormancy but may increase seed longevity primarily by improving low-temperature tolerance and overwintering ability in soil. These results provide insights into the adaptive significance of the red pericarp trait in temperate environments, although our data are limited to a cultivated temperate <i>japonica</i> (Koshihikari) background.