Root-Leaf Continuum Traits to Improve Resilience of Rice to Water-Deficit Condition.

Studies addressing root morphological and anatomical parameters connecting above ground leaf physiology including stomatal regulation, leaf structural-functional parameters affecting yield under water-deficit stress is not known either in rice or in other cereals. Towards generating such holistic knowledge at the whole plant level, representative accessions of Oryza species from different ploidy and dryland cereals including maize and sorghum were phenotyped for root anatomical traits under non-stress conditions in Experiment 1. Accessions (O. meyeriana and O. granulata) having strong root anatomical (lager stele in proportion to root diameter, SD:RD) similarities to dryland cereals were identified. In Experiment 2, along with these two wild rice accessions, lowland (IR64) and upland (N22) rice varieties were compared with sorghum for understanding root (SD:RD and late metaxylem characteristics)-leaf (stomatal size and density) alterations under non-stress (100% field capacity; FC) and 55-60% FC (water-deficit) conditions coinciding with panicle initiation (PI) and flowering. Limited water supply during PI and flowering displayed substantial plasticity in root and leaf morph-anatomical-functional traits including gas exchange, stomata behavior, leaf area, biomass and yield. Both under non-stress and water-deficit conditions, SD:RD was positively correlated with a fewer large stomata, while late metaxylem diameter was positively correlated with gas exchange, biomass and yield. The drought sensitive rice ‘IR64’ with smaller SD:RD, larger late metaxylem diameter along the root positions were associated with high density of small sized stomata resulted in greater reduction in gas exchange compared with GG genome accessions (O. meyeriana and O. granulata) and dryland sorghum under water-deficit stress. Information generated on root-leaf continuum traits will help to harness proxy traits for belowground traits using above ground parameters, which could enable designing a novel ideotype for water-limited rice ecosystems.