Rice Genotypes with SUB1 QTL Differ in Submergence Tolerance, Elongation Ability during Submergence and Re-generation Growth at Re-emergence

Rice is often the only cereal that can be grown in flood prone ecosystem. Uncertainty of rainfall is a major factor affecting the rice yield in India, Bangladesh, and Myanmar with flash flood affecting the plant stand seriously depending on duration of submergence stress which is considered as the third most important constraint to high yield in India, particularly is in the eastern Indian States (Sarkar et al. [2006]; Sarkar et al. [2009a]). Excessive flooding poses risks to human life and is a major contributor to the poverty and vulnerability of marginalized communities especially women and children in poor families (Douglas [2009]). It is estimated that the flood-affected area has more than doubled in size from about 5% (19 million hectares) to about 12% (40 million hectares) of India’s geographic area (World Bank Report [2008]). Adding to these already high risk areas, the climate projections suggest that temperatures, precipitation and flooding, and sea level rise are likely to increase, with adverse impacts on crop yield and farm income in Southeast Asia (Unnikrishnan et al. [2006]; Wassmann et al. [2009]; [INCCA 2010]). Rice in these areas is the major crop providing food for millions of subsistence farming families. Present and anticipated global food demands further necessitate a significant increase in crop productivity on less favorable farmlands and under the adversary of climate change.Quiescence and elongation are two opposite strategies by which rice adapts to flood depending upon the nature of flooding (Luo et al. [2011]). The ethylene response factors genes Snorkel1 (SK1) and Snorkel2 (SK2) allow rice to adapt to deep water whereas Submergence1A-1 (Sub1A-1) allows rice to acclimatize under flash flooding (Xu et al., [2006]; Hattori et al., [2009]; Nagai et al., [2010]). Both SKs genes and Sub1A-1 are connected with gibberellin biosynthesis or signal transduction, yet deepwater and submergence-tolerant rice seem to have opposite flooding response; n