Plant breeding for flood tolerance: Advances and limitations

Over 17 million km² of land surface is affected by flooding every year, resulting in severe damage to plants and associated losses in agricultural production around the globe. While importance of plant breeding for waterlogging stress tolerance has been long on the agenda, the progress in the field is handicapped by the physiological and genetic complexity of this trait. In this chapter, we summarise the recent knowledge about the major constraints affecting plant performance in waterlogged soils and discuss the mechanisms employed by plants to deal with the stress. The topics covered include oxygen availability in flooded soils; whole-plant responses to oxygen deprivation; biochemical alterations in hypoxic roots; mechanisms of aerenchyma formation; the role of ethylene signalling and programmed cell death in hypoxic roots; oxygen transport from shoot to root; formation of ROL barrier and control of oxygen loss; changes in soil redox potential under flooding; Mn and Fe toxicity in waterlogged plants; secondary metabolite toxicity and plant adaptation to organic phytotoxins; MAS approach to plant breeding for flooding stress tolerance; and emerging areas such as elucidating the role of membrane transporters in flooding tolerance, developing high-throughput technology platforms for fine QTL mapping and understanding ROS signalling in flooding stress tolerance.