Translating Flood-Tolerance Biology into Breeding: A 5D Framework for Next-Generation Rice Varieties.

Flooding is among the most devastating abiotic stresses limiting rice productivity. Although SUB1A introgression conferred submergence tolerance in several mega-varieties, this single-gene approach is insufficient for the diverse flood types-flash floods, stagnant floods, anaerobic germination, and deepwater inundation-progressively intensifying with climate change. Here, we review the physiological mechanisms and genetic architecture underlying tolerance to each flood type, emphasizing the dual role of reactive oxygen species (ROS) in signalling and damage, the management of elemental toxicities (Fe2+, Mn2+) under altered soil redox, and lessons from wetland species and lowland rice. We then examine why marker-assisted selection has failed for polygenic, multi-stress tolerance and identify persistent breeding bottlenecks. Building on this biological foundation, we outline an integrated 5D framework (Demand, Discovery, Design, Development, Deployment) that links gene-bank diversity, multi-omics discovery, predictive breeding and on-farm validation through continuous feedback. We discuss how connected breeding, the transition-from-trait-to-environment (TTE) strategy, and speed breeding can accelerate genetic gain, and we close with research priorities centred on the biology of multi-flood tolerance to develop climate-resilient rice.