Functional roles of the plasticity of root system development in biomass production and water uptake under rainfed lowland conditions

Abstract Fluctuation of soil moisture conditions between wet and dry is a normal occurrence in rainfed lowland and irrigated rice fields where water saving production systems are implemented, which can constrain rice productivity. In this study, we evaluated the functional roles of root plasticity for water uptake and dry matter production under such fluctuating water stress conditions. Introgression lines (INLs) of IR64, whose yield performances were previously evaluated in aerobic fields, were evaluated in the field and greenhouse under soil culture conditions using slant tube and root box methods. Under field conditions, greater root system development of INLs YTH183 and YTH304 in shallow soil layers contributed to greater shoot dry matter production than that of IR64. Furthermore, the line YTH183 responded sharply to rewatering after drought in slant tube and root box systems by increasing root elongation and branching, which contributed to its higher shoot dry matter production and water extraction compared to IR64. Such growth responses to the different soil water regimes reflect the plastic root growth response of this INL. These results imply that the plasticity in root system development in response to rewatering after drought contributed to the promotion of shoot dry matter production. Since the INLs in this study are highly genetically similar, future work will focus on pinpointing the genetic control of rice root plasticity under rainfed lowland conditions.