Chapter 10 - Physiological and genomic approaches for improving tolerance of flooding during germination and seedling establishment in rice

Abstract

Anaerobic conditions either anoxia or hypoxia caused by flooding at seed germination severely impact crop establishment under both rainfed and irrigated cultivation systems. Flooding is one of the most destructive natural hazards and a major stress constraint to rice production throughout the world, which results in huge economic losses. Approximately one-fourth of the global rice crops (ca. 40 million hectares) are grown in the rainfed lowland that is prone to seasonal flooding. Flooding reduces overall seedling survival both in controlled and field conditions, but the anaerobic condition potential gene AG1-AG2 introgression has greater tolerance under hypoxia or anoxia due to flooding stress. Our understanding of the mechanisms involved in the adaptation and tolerance of rice to flooding/anaerobic conditions especially the seed germination stage has significantly progressed in the last decades. It appears that mapping and identification of AG1-AG2 quantitative trait loci have led to the development of a marker-assisted selection breeding approach to improve flooding-tolerant rice varieties under flooding during germination. A better understanding of molecular genetics and adaptation mechanisms that enhance flood-tolerant varieties under flooding during germination needs to be reviewed. This chapter aims to review and update current knowledge on the physiological and molecular mechanisms that contribute to tolerance of flooding/anaerobic conditions in rice. We also discussed different types of flooding stress; the environmental characterization of flood water; the impact of flooding stress on rice plants; and their morphological, physiological, and metabolic responses under flooding. A brief discussion on the tolerance mechanism in rice exhibited to different types of flooding is focused on the future crop improvement program for the development of flooding-tolerant rice varieties.