Enforced Early Development of Adventitious Roots Increases Flooding Tolerance in Soybean

Adventitious roots are often developed from soybean stem by farmer's soil-heaping practice especially in East-Asian countries. Here, we examined the possibility of mitigating flooding injury by the development of adventitious roots. The high soil-moisture after soil-heaping greatly stimulated the development of adventitious roots. Soybean yield increased 11 and 26% compared to the control by soil-heaping at the R1 stage and by saturated soil-moisture treatment for 10 days after soil-heaping, respectively. The yield decrease caused by flooding was considerably mitigated by keeping adventitious roots emerged during 10 days of flooding alive by soil-heaping after the flooding. Effect of early development of adventitious roots on the mitigation of flooding injury was also evaluated using four soybean cultivars differing in the ability to develop adventitious roots. Adventitious roots were developed by one-day flooding pretreatment right after soil-heaping at the V2 stage. In all four cultivars examined, the decrease of growth and yield by flooding at the V5 or R2 stage was mitigated by soil-heaping and flooding for one day, which promoted adventitious root development. Furthermore, the higher the number of adventitious roots, the less flooding injury that occurred. Our results indicate that early development of adventitious roots by a brief saturation of soil-moisture or flooding right after soil-heaping not only increases soybean growth and yield but also enhances its flooding tolerance.