Exploring Rice and Sorghum Roots– Can Root Anatomical Modification Increase Drought Tolerance in Rice?.

Sustaining global food security is increasingly becoming a challenge under rapidly changing climate, particularly with the predicted increase in frequency and magnitude of drought stress. Flooded rice plays a key role in meeting the caloric requirement for almost half the world population, but is known to be extremely sensitive to drought stress. Plasticity in root anatomical traits between Oryza species (21 wild accessions, lowland: IR64 and upland rice: N22) and sorghum under non-stress was explored. Nodal root anatomy at two different positions i.e. root-shoot junction (RSJ) and 6 cm from the root apex was targeted. Sorghum possess distinctive adaptive root anatomical traits such as higher stele diameter and its proportion to root diameter (SD:RD), higher late meta xylem numbers and larger late meta xylem diameter, compared to Oryza species under non-stress conditions. Interestingly, only GG genome of Oryza species including O. granulata and O. meyeriana had promising below-ground root anatomy similar to sorghum at RSJ. Further, rice (IR64, N22 and GG genome) and sorghum accessions were exposed to non-stress (100 % FC) and drought stress (60 % field capacity) conditions at vegetative and reproductive stages, independently. Anatomical assessment including the root (both the RSJ and the root apex), peduncle and the stomata, to quantify the root-stem-leaf anatomical continuum affecting drought stress response in rice and sorghum were examined. Additionally, physiological (gas exchange and water use efficiency) and morphological (leaf area and biomass) traits were quantified and their relationship with yield and yield components was established under non-stress and drought stress conditions. Promising anatomical and physiological aspects of better adaptability of upland cereal sorghum to water limited conditions will be discussed, in the context of alternative breeding opportunities to enhance drought tolerance in highly sensitive rice genotypes.