Flooding tolerance in Rice: adaptive mechanism and marker-assisted selection breeding approaches

Natural and man-made ecosystems worldwide are subjected to flooding, which is a form of environmental stress. Genetic variability in the plant response to flooding involves variations in metabolism, architecture, and elongation development that are related with a low oxygen escape strategy and an opposing quiescence scheme that enables prolonged submergence endurance. Flooding is typically associated with a decrease in O2 in the cells, which is especially severe when photosynthesis is absent or limited, leading to significant annual yield losses globally. Over the past two decades, considerable advancements have been made in understanding of mechanisms of rice adaptation and tolerance to flooding/submergence. The mapping and identification of Sub1 QTL have led to the development of marker-assisted selection (MAS) breeding approach to improve flooding-tolerant rice varieties in submergence-prone ecosystems. The Sub1 incorporated in rice varieties showed tolerance during flash flood, but not during stagnant conditions. Hence, gene pyramiding techniques can be applied to combine/stack multiple resistant genes for developing flood-resilient rice varieties for different types of flooding stresses. This review contains an update on the latest advances in understanding the molecular mechanisms, metabolic adaptions, and genetic factors governing rice flooding tolerance. A better understanding of molecular genetics and adaptation mechanisms that enhance flood-tolerant varieties under different flooding regimes was also discussed.