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While improved crop water‐deficit tolerance is considered of primary importance, many phenotyping efforts focusing on quantifying structural root traits make assumptions about architecture representing root function. Therefore, the aim of this study was to quantify whole plant water‐use traits among disparate peanut (Arachis hypogaea L.) genotypes and determine their impact on water‐deficit tolerance. Mini‐rhizotrons were installed to evaluate genotypic root architecture and developmental changes to two irrigation regimes imposed during early development. Following the early‐season irrigation regimes, above‐ and below‐ground traits were studied across a range of soil water conditions through measures of: (a) leaf‐level gas exchange and (b) soil water depletion quantified using a novel soil water probe inserted into mini‐rhizotrons allowing for matched root architecture and soil water depletion measures. While differential water treatments influenced root system architecture development among the genotypes, soil water depletion locations were primarily determined by water availability in the soil profile, not simply by having greater root length at a given soil location. This contradicts the assumption that greater root presence is a consistent indicator of increased root activity. Phenotypic selection of root traits for improving the efficiency of crop water use should consider both structural and functional traits in relation to the intended production environments slated for future cultivar development. [ABSTRACT FROM AUTHOR]

Many crop species, including cultivated peanut (Arachis hypogaea L.), modify their above‐ and below‐ground growth to cope with water deficit stress. This acclimation to water deficit often triggers a biomass partitioning shift—allocating more biomass to the roots, to increase the accessibility of roots to water resources. However, additional carbon partitioning to roots may not always translate into increased water use and maintenance of aboveground biomass (ABM) and yield. Therefore, selecting an efficient root system architecture (RSA) should aim to sustain a high ABM production under a water deficit scenario. To better understand the associations of above and belowground biomass partitioning under moderate water deficit, this study evaluated the genotypic stability of 40 peanut genotypes in ABM and RSA in greenhouse experiments and further assessed genotypic differences in 4 site‐year field experiments. Our results suggested that higher ABM‐producing genotypes generally had high plasticity when subjected to water deficit whereas the low ABM‐producing genotypes had relatively high stability. Hierarchical clustering analysis further revealed that genotypes with a high root‐to‐shoot ratio potentially had increased genotypic stability in ABM underwater deficit. Interestingly, genotypes that maintained the highest ABM underwater deficit did not have the highest total root biomass and length. Instead, these genotypes had the highest root length in the top layer of soil (0–0.3 m) and relatively fewer roots in the deeper layer of soil (0.3–1 m). Greenhouse‐screened stable genotypes exhibited minimal yield reduction when subjected to mid‐season water deficit in some of the field validation experiments, but it also happened to some plastic genotypes, indicating that further validation of controlled environment screenings for genotypic water‐deficit tolerance in the field is necessary. [ABSTRACT FROM AUTHOR]