Changes in Water Uptake and Cotyledon Morphology during Imbibition among Individual Soybean Seeds of the Same Variety and the Impact on Plant Emergence

Abstract

Imbibition damage leads to poor early growth in soybean seeds exposed to excessive soil moisture. Rapid water imbibition hampers germination and emergence, even before cotyledons are not sufficiently swollen. Therefore, interindividual variations in amount of water absorption, localization of absorbed water, and morphology of seeds were examined to clarify the mechanism underlying imbibition damage. Furthermore, the relationship between water absorption and plant emergence was examined. Seeds of cultivar “Satonohohoemi” were soaked in water for 10–90 minutes. During soaking, the seed morphology was examined, water intake was quantified, and magnetic resonance images were captured. After seeds were soaked, seed germination and plant emergence rates were assessed. The soaked seeds were classified as normal and over-absorbed seeds. The over-absorbed seeds were further classified into those without a gap between the cotyledons (CL seeds) and those with a gap (OP seeds). The unimpaired seed rates of normal, CL, and OP seeds were 98.3%, 66.7%, and 20.0% after 10 minutes of soaking treatment, the difference being significant. Plant emergence rates of normal, CL, and OP seeds were 93.3%, 53.3%, and 23.3%. Wide interindividual variations in amount of water absorption and morphological change were observed in the same lot of seeds. In addition, water intrusion between the cotyledons was suggested to affect the germination and emergence.