Adaptation of Legume Seeds to Waterlogging at Germination

Abstract

Legume seeds are often sown on standing rice crops a few weeks before rice harvest (relay cropping). Seeds cannot germinate in waterlogged soil under relay sowing as oxygen is depleted. However, seeds may survive under soil waterlogging if the seeds can initiate anaerobic respiration, have a large seed reserve such as carbohydrates, perform a slow water uptake during imbibition and are small in size. An example of a seed crop that can initiate anaerobic respiration is rice. The seed embryo of rice can use an alcoholic fermentation pathway from carbohydrates to produce enough energy to germinate. In legumes, seeds with a slow imbibition rate were more waterlogging tolerant than seeds with a rapid rate. This is likely due to seeds with low imbibition rates having less electrolyte leakage than seeds with a rapid imbibition rate during germination under waterlogging. A small amount of oxygen may remain on the surface of waterlogged soil. Small seeds can use the small amount of oxygen on the surface of waterlogged soil to germinate. However, large seeds often fail to use the oxygen on the surface of waterlogged soil to germinate because only a small part of large seeds remain on the surface of waterlogged soil. Therefore, small seeds are more adapted to soil waterlogging than large seeds under relay cropping. This review is focused on the physiological adaptation of legume seeds under low oxygen concentration during soil waterlogging.