Heritable variation in root emergence during post-drought recovery reveals potential links to seedling drought recovery in rice

Abstract

Drought stress is a significant factor limiting rice yields worldwide. Effective drought tolerance involves both the ability of a plant to withstand water-limited conditions and the capacity to recover after rehydration. As rainfall patterns shift due to climate change, adaptation to variations in water availability during the growth period becomes increasingly important. Given the critical role of crown root number and length in drought response, understanding these traits is crucial. In this study, we evaluated the ability of rice genotypes to produce new crown roots following drought stress, using both a QTL mapping population and a diverse set of 3K-Rice Genomes Project accessions. Our results revealed high heritability (H² = 0.65) for new root number (NRN), as well as significant genotypic variation in NRN and new root length (NRL) during recovery. They are independent of general root vigor or drought tolerance under stress. A newly developed, simple screening method was validated in greenhouse and field trials, showing consistent genotype-specific responses, with a significant correlation (R = 0.73, p = 0.007). Varieties such as DJ123 and CHILE BORO maintained high NRN values under both water bath and soil-based recovery conditions, whereas IR64, despite producing many roots, showed limited recovery potential. Candidate loci associated with recovery-related root traits partially overlapped with known QTL for rooting ability and drought response, indicating both novel and previously characterized genomic regions. Our findings demonstrate that new root development during recovery is a distinct and heritable trait with potential for use in breeding programs.