Elucidating the genetic control of rooting behavior under water-deficit stress is essential to breed climate-robust rice (Oryza sativa) cultivars. Using a diverse panel of 274 indica genotypes grown under control and water-deficit conditions during vegetative growth, we phenotyped 35 traits, mostly related to root morphology and anatomy, involving 45,000 root-scanning images and nearly 25,000 cross sections from the root-shoot junction. The phenotypic plasticity of these traits was quantified as the relative change in trait value under water-deficit compared with control conditions. We then carried out a genome-wide association analysis on these traits and their plasticity, using 45,608 high-quality single-nucleotide polymorphisms. One hundred four significant loci were detected for these traits under control conditions, 106 were detected under water-deficit stress, and 76 were detected for trait plasticity. We predicted 296 (control), 284 (water-deficit stress), and 233 (plasticity) a priori candidate genes within linkage disequilibrium blocks for these loci. We identified key a priori candidate genes regulating root growth and development and relevant alleles that, upon validation, can help improve rice adaptation to water-deficit stress.

District of Columbia 20005 (P.S.B.)Water scarcity and the increasing severity of water deficit stress are major challenges to sustaining irrigated rice (Oryza sativa) production. Despite the technologies developed to reduce the water requirement, rice growth is seriously constrained under water deficit stress compared with other dryland cereals such as wheat (Triticum aestivum). We exposed rice cultivars with contrasting responses to water deficit stress and wheat cultivars well adapted to water-limited conditions to the same moisture stress during vegetative growth to unravel the whole-plant (shoot and root morphology) and organ/tissue (root anatomy) responses. Wheat cultivars followed a water-conserving strategy by reducing specific leaf area and developing thicker roots and moderate tillering. In contrast, rice 'IR64' and 'Apo' adopted a rapid water acquisition strategy through thinner roots under water deficit stress. Root diameter, stele and xylem diameter, and xylem number were more responsive and varied with different positions along the nodal root under water deficit stress in wheat, whereas they were relatively conserved in rice cultivars. Increased metaxylem diameter and lower metaxylem number near the root tips and exactly the opposite phenomena at the rootshoot junction facilitated the efficient use of available soil moisture in wheat. Tolerant rice 'Nagina 22' had an advantage in root morphological and anatomical attributes over cultivars IR64 and Apo but lacked plasticity, unlike wheat cultivars exposed to water deficit stress. The key traits determining the adaptation of wheat to dryland conditions have been summarized and discussed.Among cereals, rice (Oryza sativa) and wheat (Triticum aestivum) are the most important staple food crops, and they belong to the family Poaceae. These two cereals share a common ancestor and diverged about 65 million years ago (Sorrells et al., 2003). Rice eventually developed strong adaptation potential for fully flooded conditions across tropical to temperate environments, while wheat became well adapted to aerobic conditions mostly restricted to temperate environments. Rice, with a semiaquatic behavior, consumes about 30% of the total fresh water available for agricultural crops worldwide, which equates to a 2-to 3-fold higher consumption than other cereals such as wheat and maize (Zea mays; Peng et al., 2006). Despite a significantly lower water requirement, the potential yield of wheat in a favorable environment (9 tons ha 21 ) is comparable with the yield of fully flooded rice (9 tons ha 21 ) in the dry season at the International Rice Research Institute (IRRI; Fischer and Edmeades, 2010). Hence, rice records very low water productivity compared with wheat and other dryland cereals. Because of growing concerns about water scarcity and the increased frequency and magnitude of water deficit stress events under current and future climates, increasing or even sustaining rice yield under fully flooded conditions is highly challenging. To minimize the total water requ...

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The metabolic-oxidative stress profile of the rice flag leaf during drought stress in the reproductive stage is highly predictive for grain yield loss sensitivity of 292 accessions at harvest time.