Maintained root length density contributes to the waterlogging tolerance in common wheat (Triticum aestivum L.)

• Common wheat was exposed to waterlogging from jointing to maturity.
• The cultivars with higher root length density showed higher grain yield.
• Maintained root length density is necessary for waterlogging tolerance in common wheat.

Waterlogging stress substantially reduces the growth and yield of common wheat (Triticum aestivum L.). Limited root development due to decreased availability of oxygen in roots is the major growth-limiting factor for plants under waterlogged conditions. In this study, we have determined whether a maintained root length density can be one of the important traits for waterlogging tolerance to maintain the shoot growth and grain yield, using waterlogging-tolerant and -susceptible wheat cultivars. This study was carried out over five consecutive cropping seasons (from 2006 to 2010), and the wheat plants were exposed to waterlogging from jointing stage to maturity. The waterlogging-tolerant cultivars Nishikazekomugi and Iwainodaichi showed higher relative grain yield and whole grain ratio under waterlogged conditions than the susceptible UNICULM. The waterlogging-tolerant cultivars maintained higher leaf water potential, stomatal conductance and photosynthetic rate under waterlogged conditions than the susceptible one, which was consistent with the higher relative root length density in the tolerant cultivars. These results indicate that maintained root length density is related to maintaining water uptake and the resultant photosynthesis and yield production in common wheat grown under waterlogged conditions.