Submergence is a common problem in rainfed lowland rice cultivation in Bangladesh. Submergence stress adversely affects about 15 million ha of ricegrowing areas in the rainfed lowlands in South and Southeast Asia each year. The extent of submergence stress has recently increased because of extreme weather events such as the unexpected heavy rains that inundated wide areas across many regions in Asia. Moreover, climate projections indicate a likely increase in temperature, precipitation and flooding, and sea level, with adverse impacts on crop yield and farm income in Southeast Asia (Wassmann et al 2009). In Bangladesh, flash floods normally occur once or twice per year (sometimes more often), especially in the country’s northwestern part, due to recent changes in climate (Mazid et al 2012). One of the most promising solutions is to develop high-yielding varieties that can tolerate submergence and are most likely to be adopted by farmers in the target regions. IR64 is the parent of NSIC Rc 194 (Submarino 1), which was released in the Philippines in 2009. The parent of Swarna-Sub1 is Swarna (MTU 7029), which was released in India in 2009. The Bangladesh Rice Research Institute (BRRI) released the same variety as BRRI dhan51 in 2010; in the same year, BRRI released another submergence-tolerant rice variety, BRRI dhan52, an introgression line of BR11 carrying the SUB1 gene.