Rainfed lowland rice is grown under fluctuation of soil moisture conditions between wet and dry due to the unpredictable rainfall. For rainfed lowland rice, various intensities of drought and soil moisture fluctuation are critical stresses which can constrain rice productivity. In addition, the irrigated rice when water saving cultivation technology is implemented may experience soil moisture fluctuation stress due to the intermittent irrigation. We focused on the root plasticity as a key root trait for plant’s adaptation to such water stress under rainfed lowlands and irrigated lowlands with water saving cultivation systems. Chromosome segment substitution lines and IR64 introgression lines were used to evaluate the functional role of root plasticity. To evaluate the plasticity in root system development, we used the several methods to quantitatively evaluate the root plasticity such as large scale field experiment and detailed analysis by using root-box pinboard method. The root morphological trait and its genetic control for root plasticity expressions differed depending on the type of water stress. It was also shown quantitatively that developmental root plasticity triggered by water stress effectively contributed to dry matter production through enhanced water uptake. Furthermore, the expression of root plasticity was affected by the level of nitrogen application, indicating that root plasticity can be enhanced by cultivation technics.

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