Field plot test of submergence tolerance of Sub1 and non-Sub1 varieties. The SUB1 locus from FR13A was introduced into the rice varieties IR64 and Samba Mahsuri by marker-assisted backcrossing and into IR49830-7-1-2-2 through conventional breeding. A field trial performed at IRRI in 2007 included Sub1 lines, the progenitors, and IR49830-7-1-2-2 (tolerant, used as SUB1 donor) and IR42 (sensitive) as checks. Fourteen-day-old seedlings were transplanted into a field with high levees, grown for 14 days and then completely submerged with about 1.25 m of water for 17 days. The field was drained, and the plants were allowed to recover under non-stress conditions. The photograph shows the performance of the lines about 60 days after de-submergence.