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Soybean (Glycine max L. Merr.) cultivars from the U.S. are generally intolerant to flooding stress. Soybean
germplasm and cultivars originating from other countries and grown in rotations with paddy rice potentially could have
better flooding tolerance. Screen-house and field tests were conducted to determine variations in flooding tolerance
among 21 soybean varieties from Southeast Asia. Flooding for two weeks at the R2 growth stage reduced grain yield under
field conditions between 36% and 100% (all plants dead). However, plants that survived were, on the average, 13%
taller than control plants. Tolerance to R2 flooding was associated with higher number of pods per plant and 100-grain
weight. Growth response to flooding stress, as determined by plant height, was correlated with grain yield in all three environments.
While there was no correlation in yield between field and screen-house tests, the flood tolerance ranking of
the field test was correlated with the ranking of one screen-house test. Screen-house tests could distinguish tolerant from
susceptible varieties based on plant survival and grain yield. Three varieties - VND2, Nam Vang and ATF15-1 - showed
the best flooding tolerant responses under field and screen-house conditions. These lines provide new germplasm resources
for the genetic improvement of flooding tolerance in soybean.