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

## TL;DR

This study shows that the red pericarp trait in rice, controlled by Rc and Rd genes, improves seed survival in cold conditions but does not cause deep dormancy.

## Contribution

The combined effect of Rc and Rd on freezing tolerance and overwintering ability is newly demonstrated in rice.

## Key findings

- NILs with both Rc and Rd showed higher freezing tolerance than other lines.
- Red pericarp increases seed longevity through cold tolerance, not dormancy.
- Lines with Rc or Rd alone failed to survive winter unlike weedy rice controls.

## Abstract

The red pericarp trait is controlled by Rc and Rd, 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’ Rc and/or Rd 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 Rc, Rd, 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 Rc and Rd 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 japonica (Koshihikari) background.

This study shows that the red pericarp trait, controlled by Rc and Rd, does not by itself confer deep seed dormancy in rice. Using near isogenic lines in a temperate japonica background, we demonstrate that the combined action of Rc and Rd markedly enhances seed freezing tolerance and overwintering survival in soil. These findings suggest that red pericarp contributes to seed persistence primarily through improved cold tolerance rather than dormancy.