Flash flood + Stagnant flood

Rainfed shallow and semi-deep water lowland rice suffer from flash floods and waterlogging. Flash floods occur due to the overflow of rivers and canals because of heavy and intense rainfall events and sometimes due to tidal movements in coastal areas. Rice varieties with 140-155 day duration are usually cultivated in these flood-prone areas.
Three genes SUB1A, SUB1B, and SUB1C were identified within the Sub1 (QTL) region of which SUB1A was subsequently identified as the major determinant of submergence tolerance.
Marker-assisted backcross (MABC) breeding system was used to incorporate this gene into elite rice varieties. The new varieties with SUB1A retain the entire genome of the original varieties having a small segment of the donor genome containing Sub1 (QTL) gene. These varieties possess all characteristics of original parental lines except for the added trait of submergence tolerance.
Swarna-Sub1 was released for cultivation in 2009 in India and performed better under flood situation apart from being high yielding with good grain quality. Wide adaptability of Sub1 varieties is important because flood incidences are becoming more erratic in recent years.