The study was conducted in experimental fields of the Ubon
Rice Research Center (URRC), Thailand, in the wet seasons of 2010
and 2011. The soil is light in texture, permitting high percolation
and loss of water, and classified as loamy sand. Twenty rice
(Oryza sativa L.) genotypes with a wide genetic background with
respect to adaptations to aerobic conditions were used for the 2010
and 2011 experiments (Table 1), including seven and eight genotypes
from double haploid lines (DHLs) and backcross lines (BCLs),
respectively. DHLs were developed from a cross between CT9993-
5-10-1-M (upland japonica) and IR62266-42-6-2 (lowland indica)
and include large genotypic variation with respect to drought tolerance
(Zhang et al., 2001). BCLs were Surin1 (rainfed lowland rice)
backcross introgression lines with IR68586-FA-CA-143, which is
one of the DHLs identified as drought tolerance (Jongdee et al.,
2006).