Role of Roots for Stabilizing Rice Production under Water Stress Conditionst

Water stress is the major factor that determines the rice productivity, which includes drought under upland conditions, and moisture fluctuations in rainfed lowland and possibly in irrigated fields with water-saving production technology like aerobic rice cultivation. The response of root system to a certain soil environmental condition in turn largely determines the plant’s ability to adapt to the condition. The ability of the plant to change its morphology, as environmental conditions change is known as phenotypic plasticity. We showed that the root system development and their plastic responses to drought are under different QTL control. We further showed that root osmotic adjustment is one of the physiological bases for the plasticity. We then used chromosome segment substitution lines to identify desirable root traits under water stress conditions and to evaluate the functional significance of the target traits with greater precision because of the minimal confounding effects of other traits. We found that the lines exhibiting plastic root system development in response to drought and those with plastic lateral root development and aerenchyma formation in response to transient drought and O2 deficient conditions showed better adaptation to respective condition. Further study is in progress to more precisely identify the QTL responsible for the root plasticity under various intensities and types of water stresses and to examine quantitatively the physiological function of such plasticity for plant adaptation and productivity.