Genetic variations in dry matter production, nitrogen uptake, and nitrogen use efficiency in the AA genome Oryza species grown under different nitrogen conditions

To clarify the genotypic variation of nitrogen (N) response in the AA genome Oryza species, we investigated dry matter production, N uptake, N and water use efficiencies (NUE and WUE), bleeding sap rate (BR), and root morphological traits at vegetative stage in 6 cultivars and 4 strains of 6 species (O. sativa, O. glaberrima, O. barthii, O. nivara, O. meridionalis, and O. rufpogon) grown under standard N (SN) and low N (LN) conditions. Some wild Oryza strains and O. glaberrima showed high dry matter production under both N conditions. In most plants, total dry weight decreased and root dry weight increased under the LN condition, resulting in decreased top-root ratio. In japonica cultivars of O. sativa, however, these traits were unaffected by the N condition. There were no significant differences in WUE with plant species or N conditions. In all plants, however, NUE was higher in the LN than SN condition, and was conspicuously high in most wild Oryza species and O. glaberrima. Some of them showed increased capacity of nitrate-N (NO₃-N) uptake under the LN condition. In cultivars and strains with a high NUE, root dry weight, root surface area, and BR were also higher under the LN condition. These results suggest that a high NUE is associated with the development of a root system, increased BR, and probably increased capacity of NO₃-N uptake. This study revealed the presence of superior wild Oryza strains for growth under LN that may be a promising genetic resource for low N-input agriculture.