Relationship between mineral coating on roots and yield performance of wheat under waterlogging stress

Waterlogging stress limits the productivity of winter wheat (Triticum aestivum L. emend. Thell.) in many parts of the world. When wheat is grown under waterlogged conditions, a reddish-brown mineral coating can form on the epidermal surface of the roots. In wetland plants such as rice, the amount of mineral coating formed on root surfaces is positively related to yield. This study was conducted to determine whether mineral coating on the roots of wheat is related to yield potential under waterlogged conditions. Root mineral coatings formed under waterlogged conditions were studied in 12 cultivars and two breeding lines over three years of greenhouse pot studies. Soil redox potential in the waterlogged treatment ranged between - 46 and 171 mV, and grain yield was suppressed by 28–49% compared to well-drained controls. Mineral coating formed on the roots from the waterlogged treatment was determined to be composed primarily of iron, based on ICP elemental analysis, iron-specific staining, and ion-mapping by scanning electron microscopy using an X-ray detector. Of 11 elements quantified by ICP spectroscopy, six were significantly affected by waterlogging treatment, and three of these, Fe, Mn and P, were well-correlated negatively to yield. Aerenchyma formation in the heavily coated waterlogged roots appeared to disrupt the internal root structure, and exceeded 40% of cross-sectional area in one cultivar. Unlike rice, which shows a positive relationship between oxygen release from roots, grain yield and mineral coating, in winter wheat, the amount of mineral coating is negatively related to grain yield under waterlogged conditions.