Differences in elongation growth between floating and deepwater rice plants grown under severe flooding in Thailand

• Under severe flooding condition, survival rates of DWR were lower than those of FR.
• Low survival of DWR is due at least in part to lower rate of internode elongation.
• Internode elongation of FR was at a rate equal to that of the rise in water level.
• FR can properly modulate the rate of internode elongation according to water level.

To compare growth responses of floating rice (FR) and deepwater rice (DWR) to severe flooding conditions, two FR varieties, Plai Ngahm Prachinburi and Pin Gaew 56, and two DWR varieties, Prachinburi 2 and Hawm Prachinburi (RD45), were grown in the floating rice field of Prachinburi Rice Research Center in Thailand in 2007 and 2008. The water depth in the research field exceeded 1 m from September to October in both 2007 and 2008. Although the plant length of the two DWR varieties increased at a slower rate than those of the FR varieties, the DWR varieties kept parts of their foliage above the water surface. However, the survival rates of the DWR varieties were lower than those of the FR varieties under these conditions. The rates of internode elongation of the DWR varieties were slower than those of water level rise, whereas those of the FR varieties were almost equal. Consequently the tops of the uppermost leaf sheath in the FR varieties were always above the water level. These results suggest that FR can regulate internode elongation in response to rising water level so as to keep the top of the uppermost leaf sheath above the water surface.