Physiological basis of submergence tolerance in rainfed lowland rice ecosystem

The rainfed lowland rice ecosystem is affected by not only water deficit but also excess water. Nearly half of the ecosystem is prone to submergence damages caused by flash flooding. Although the rice plant is well adapted to aquatic environments, it is unable to survive if it is completely submerged in water for an extended period. Germplasm improvement for submergence tolerance is likely to be the best option available for alleviation of the submergence damages, other than construction of extensive drainage systems which require a large investment. The germplasm improvement may be successful if physiological mechanisms for submergence tolerance are well understood and floodwater environments are characterized. The plant response to submergence stress varies greatly depending on conditions of floodwater such as light intensity and concentrations of O-2 and CO2. This suggests that various physiological mechanisms are involved for survival from the submergence stress. This paper reviews the current understanding of submergence tolerance in rice plants from physiological aspects and then discusses possible strategies to improve the tolerance. (C) 1999 Elsevier Science B.V. All rights reserved.