Root Plasticity for Adaptation and Productivity of Crop Plants Grown Under Various Water Stresses

Roots play significant functional roles in adaptation and productivity of crop plants especially when grown under various water stresses. The ability of plant to change its morphology as environmental conditions change is defined as phenotypic plasticity. We have accumulated experimental evidence by conducting a series of experiments that attempt to determine the functional roles of root plasticity by using various accessions/populations, and root plasticity has been phenotyped by using a range of methods. The results have consistently shown that the root plasticity specifically in branching, deep rooting, the associated aerenchyma formation, and rooting angle, which is expressed in response to varied soil water conditions, substantially contribute to the maintained/promoted growth and productivity through enhanced physiological functions. Genotyping is also in progress by using some of the population to locate genes responsible for the expression of root plasticity traits. An attempt of pyramiding multiple root plasticity traits was also made to improve submergence and salinity tolerance. Further study is in progress to more precisely identify the quantitative trait loci responsible for root plasticity and to examine the physiological function of such plasticity for plant adaptation and productivity. Based on these studies, we propose an ideotype of the root system that maximizes the growth and yield under various water stress conditions with breeding and agronomic approaches.