Tolerant Responses of Soybean (Glycine max) to Soil Waterlogging Stress.

Soybean (Glycine max) cultivars from the U.S. are generally intolerant to stress from waterlogged soil. Since current U.S. soybean cultivars come from a narrow genetic base, soybeans with better soil waterlogging tolerance may be found in germplasm from other countries.  Three hundred exotic soybean plant introductions from the United State Department of Agriculture soybean germplasm collection were evaluated for tolerance to soil waterlogging in a four-year field study. The genotype PI408105A was identified as showing consistent tolerance to flooding as determined by overall plant injury. Yield tests of the plant introductions with good visual tolerance scores showed that PI408105A had less reduction (8 to 18%) in seed yield than other genotypes. Additional studies were conducted in the greenhouse to determine the flood tolerance mechanisms of the plant introduction PI408105A compared to the flood-sensitive genotype, S99-2281. PI408105A plants more rapidly developed an adaptive mechanism to flooding by producing aerenchyma and adventitious roots and were able to resume root growth after three days of flooding in comparison to the flood sensitive genotype S99-2281. Roots of PI408105A plants also contained more ATP and showed less membrane damage than roots of S99-2281 plants. Understanding mechanisms involved in tolerance will enhance development of cultivars that have the ability to overcome flooding stress for the benefit of soybean producers, especially in regions where soil drainage is either impractical or impossible.