Root anatomical traits of wild-rices reveal links between flooded rice and dryland sorghum

The root anatomical and morphological traits and their plasticity under water deficit are essential to improve adaptation of rice cultivars to water-limited conditions. We investigated wild-rice accessions along with a dryland cereal (Sorghum bicolor) for root related traits under non-stress and water deficit during panicle initiation and flowering. Wild-rices from GG genome (Oryza granulata and Oryza meyeriana) recorded high similarity with sorghum in key root anatomical parameters such as larger stele diameter in proportion to root diameter (SD:RD [%]) and more late metaxylem number (LMXN). Comparative analyses between wild-rice accessions and a diverse indica panel revealed narrow genetic variability in LMXN and SD:RD in Oryza sativa panel compared to O. granulata and O. meyeriana. Wild-rices from GG genome had a combination of favorable anatomy (larger SD:RD and more but smaller late metaxylem) and root morphology (thinner roots and higher root surface area) during panicle initiation and flowering compared to popular rice cultivar IR64. The above combination can help facilitate effective water use by regulating axial water flow under water-deficit conditions, while the opposite was noticed in the drought susceptible IR64. Novel sources for root anatomical traits identified from wild-rice accessions can be utilized in rice breeding programs to develop water-deficit stress tolerant rice cultivars.