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Plant root systems are responsible for the capture of soil water and minerals essential for their growth. With the need to reduce fertiliser use and improve resilience to extreme climate events, improving resource capture efficiency has become a hot topic in agriculture. This includes optimising root distribution in soils via appropriate root system architecture and growth. Root systems are often described using integrative variables, e.g. number and biomass, that are cost-effective but provide limited cues on root distribution. Modelling studies have shown that root systems can also be described using process variables, depicting growth and development processes. These are expected to be more closely connected to the underlying biology than the integrative variables and to lead more directly to optimisation paths. In this thesis, we created a novel high-throughput phenotyping pipeline of plants grown in aeroponics. This pipeline exploits high spatial and temporal resolution image series to estimate process variables from simple morphologic features, with very limited computing resources. It was used to analyse the genetic architecture of process and integrative variables on diversity panels of bread and durum wheat (500 genotypes) and was evaluated against independent experiments (pouches, rhizotubes and field). We demonstrated that process information can be estimated easily from simple morphologic features if dense time series are available. We also showed that lateral root formation, despite being highly variable along the root system, can be constant when cumulated at the whole plant level. Cross-experiment validation revealed that genotypic differences for process variables were largely environment-specific. Finally, the genetic architecture of process variables was not found to be simpler than that of the integrative ones. (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2022

Poster that presents the experiments, the main results and take home messages.

Poster presented during the NSABS conference held in Gembloux Belgium on the 31th of January 2020.

Over the last years, high throughput phenotyping has become increasingly popular in plant biology and breeding. But, root phenotyping has been progressing at a slower pace, mainly due to observation constraints, but also because root scientists are still not unanimous on how to represent root system morphology. Our group has developed a root phenotyping installation that allows us to evaluate root morphology at high spatial and temporal resolutions. The platform has required throughput for modern genetic quantitative experiments, it captures images that simplified segmentation and with the very high spatial and temporal resolution, it can yield quantitative root information in many different formalisms (model parameters, tracing, densities, shapes...)

Poster presented during the poster session of the 2nd annual meeting of the European project SolACE about root architecture phenotypes in bread and durum wheat.

Genetic Analysis of Dynamic Root Traits using Wheat Diversity Panels Clothilde Collet*, Patrick Thaon*, Karine Chenu, Jack Christopher, Xavier Draye. *These authors contributed equally to the work. Understanding drought tolerance mechanisms has never been so relevant, especially in view of the increasing diversity of water limited scenarios predicted by climate research. Classically, breeders target above ground traits to improve drought tolerance and a rather limited interest has been given to the root system architecture. Root traits should be considered because roots are key players of soil water extraction. In particular, special attention should be devoted to dynamic root traits in order to shift the focus towards a better understanding of drought resilience. Using time-lapse image sequences of whole root systems over three weeks, we captured dynamic information on root architecture of wheat seedlings growing in aeroponics. Three wheat diversity panels have been phenotyped: a MR-NAM bread wheat population (521 lines), a bread wheat diversity panel (250 varieties) and a durum wheat diversity panel (250 varieties). Data extraction, based on the identification and tracking of root tips in image sequences, has allowed the determination of the root growth rate, emergence, maximum length and apical diameter of primary and seminal roots. For the MR-NAM panel, a high heritability of seminal root emergence has been estimated, despite important environmental and genotype by environment variances. However, for the others seminal traits, heritability tended to be low. Efforts are ongoing to analyse lateral root traits, yet their extraction from images is challenging due the high density of lateral roots. A genome wide association study (GWAS) has been carried out with the MR-NAM population data and has led to the identification of three QTLs, related to seminal root growth rate and maximum root length. Phenotyping of the other panels are still ongoing and a meta-analysis will be conducted using GWAS results from the three panels. These experiments are part of the EU project SolACE (http://www.solace-eu.net). References: Burton, Amy L., James Johnson, Jillian Foerster, Meredith T. Hanlon, Shawn M. Kaeppler, Jonathan P. Lynch, et Kathleen M. Brown. 2015. « QTL Mapping and Phenotypic Variation of Root Anatomical Traits in Maize (Zea Mays L.) ». Theoretical and Applied Genetics 128 (1): 93‑106. https://doi.org/10.1007/s00122-014-2414-8. de Dorlodot, S., 2007. Root system architecture: a genetic analysis in rice (PhD Thesis). Université catholique de Louvain. de Dorlodot, S., Forster, B., Pagès, L., Price, A., Tuberosa, R., Draye, X., 2007. Root system architecture: opportunities and constraints for genetic improvement of crops. Trends in Plant Science 12, 474–481. https://doi.org/10.1016/j.tplants.2007.08.012 Lynch, J. 1995. « Root Architecture and Plant Productivity ». Plant Physiology 109 (1): 7‑13. https://doi.org/10.1104/pp.109.1.7. Thaon, P., 2017. Genetic analysis of wheat root architecture in aeroponics. Tuberosa, R., Sanguineti, M.C., Landi, P., Michela Giuliani, M., Salvi, S., Conti, S., 2002. Identification of QTLs for root characteristics in maize grown in hydroponics and analysis of their overlap with QTLs for grain yield in the field at two water regimes. Plant Mol Biol 48, 697–712. https://doi.org/10.1023/A:1014897607670 Wasson, A. P., R. A. Richards, R. Chatrath, S. C. Misra, S. V. Sai Prasad, G. J. Rebetzke, J. A. Kirkegaard, J. Christopher, et M. Watt. 2012. « Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops ». Journal of Experimental Botany 63 (9): 3485‑98. https://doi.org/10.1093/jxb/ers111. Welcker, C., Sadok, W., Dignat, G., Renault, M., Salvi, S., Charcosset, A., Tardieu, F., 2011. A Common Genetic Determinism for Sensitivities to Soil Water Deficit and Evaporative Demand: Meta-Analysis of Quantitative Trait Loci and Introgression Lines of Maize. Plant Physiology 157, 718–729. https://doi.org/10.1104/pp.111.176479

Understanding drought tolerance mechanisms has never been so relevant, especially in view of the increasing diversity of water limited scenarios predicted by climate research. Classically, breeders target above ground traits to improve drought tolerance and a rather limited interest has been given to the root system architecture. Root traits should be considered because roots are key players of soil water extraction. In particular, special attention should be devoted to dynamic root traits in order to shift the focus towards a better understanding of drought resilience. Using time-lapse image sequences of whole root systems over three weeks, we captured dynamic information on root architecture of wheat seedlings growing in aeroponics. Three wheat diversity panels have been phenotyped: a MR-NAM bread wheat population (521 lines), a bread wheat diversity panel (250 varieties) and a durum wheat diversity panel (250 varieties). Data extraction, based on the identification and tracking of root tips in image sequences, has allowed the determination of the root growth rate, emergence, maximum length and apical diameter of primary and seminal roots. For the MR-NAM panel, a high heritability of seminal root emergence has been estimated, despite important environmental and genotype by environment variances. However, for the others seminal traits, heritability tended to be low. Efforts are ongoing to analyse lateral root traits, yet their extraction from images is challenging due the high density of lateral roots. A genome wide association study (GWAS) has been carried out with the MR-NAM population data and has led to the identification of three QTLs, related to seminal root growth rate and maximum root length. Phenotyping of the other panels are still ongoing and a meta-analysis will be conducted using GWAS results from the three panels. These experiments are part of the EU project SolACE (http://www.solace-eu.net). References: Burton, Amy L., James Johnson, Jillian Foerster, Meredith T. Hanlon, Shawn M. Kaeppler, Jonathan P. Lynch, et Kathleen M. Brown. 2015. « QTL Mapping and Phenotypic Variation of Root Anatomical Traits in Maize (Zea Mays L.) ». Theoretical and Applied Genetics 128 (1): 93-106. https://doi.org/10.1007/s00122-014-2414-8. de Dorlodot, S., 2007. Root system architecture: a genetic analysis in rice (PhD Thesis). Université catholique de Louvain. de Dorlodot, S., Forster, B., Pagès, L., Price, A., Tuberosa, R., Draye, X., 2007. Root system architecture: opportunities and constraints for genetic improvement of crops. Trends in Plant Science 12, 474–481. https://doi.org/10.1016/j.tplants.2007.08.012 Lynch, J. 1995. « Root Architecture and Plant Productivity ». Plant Physiology 109 (1): 7-13. https://doi.org/10.1104/pp.109.1.7. Thaon, P., 2017. Genetic analysis of wheat root architecture in aeroponics. Tuberosa, R., Sanguineti, M.C., Landi, P., Michela Giuliani, M., Salvi, S., Conti, S., 2002. Identification of QTLs for root characteristics in maize grown in hydroponics and analysis of their overlap with QTLs for grain yield in the field at two water regimes. Plant Mol Biol 48, 697–712. https://doi.org/10.1023/A:1014897607670 Wasson, A. P., R. A. Richards, R. Chatrath, S. C. Misra, S. V. Sai Prasad, G. J. Rebetzke, J. A. Kirkegaard, J. Christopher, et M. Watt. 2012. « Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops ». Journal of Experimental Botany 63 (9): 3485-98. https://doi.org/10.1093/jxb/ers111. Welcker, C., Sadok, W., Dignat, G., Renault, M., Salvi, S., Charcosset, A., Tardieu, F., 2011. A Common Genetic Determinism for Sensitivities to Soil Water Deficit and Evaporative Demand: Meta-Analysis of Quantitative Trait Loci and Introgression Lines of Maize. Plant Physiology 157, 718–729. https://doi.org/10.1104/pp.111.176479

Understanding drought tolerance mechanisms has never been so relevant, especially in view of the increasing diversity of water limited scenarios predicted by climate research. Classically, breeders target above ground traits to improve drought tolerance and a rather limited interest has been given to the root system architecture. Root traits should be considered because roots are key players of soil water extraction. In particular, special attention should be devoted to dynamic root traits in order to shift the focus towards a better understanding of drought resilience. Using time-lapse image sequences of whole root systems over three weeks, we captured dynamic information on root architecture of wheat seedlings growing in aeroponics. Three wheat diversity panels have been phenotyped: a MR-NAM bread wheat population (521 lines), a bread wheat diversity panel (250 varieties) and a durum wheat diversity panel (250 varieties). Data extraction, based on the identification and tracking of root tips in image sequences, has allowed the determination of the root growth rate, emergence, maximum length and apical diameter of primary and seminal roots. For the MR-NAM panel, a high heritability of seminal root emergence has been estimated, despite important environmental and genotype by environment variances. However, for the others seminal traits, heritability tended to be low. Efforts are ongoing to analyse lateral root traits, yet their extraction from images is challenging due the high density of lateral roots. A genome wide association study (GWAS) has been carried out with the MR-NAM population data and has led to the identification of three QTLs, related to seminal root growth rate and maximum root length. Phenotyping of the other panels are still ongoing and a meta-analysis will be conducted using GWAS results from the three panels. These experiments are part of the EU project SolACE (http://www.solace-eu.net). References: Burton, Amy L., James Johnson, Jillian Foerster, Meredith T. Hanlon, Shawn M. Kaeppler, Jonathan P. Lynch, et Kathleen M. Brown. 2015. « QTL Mapping and Phenotypic Variation of Root Anatomical Traits in Maize (Zea Mays L.) ». Theoretical and Applied Genetics 128 (1): 93-106. https://doi.org/10.1007/s00122-014-2414-8. de Dorlodot, S., 2007. Root system architecture: a genetic analysis in rice (PhD Thesis). Université catholique de Louvain. de Dorlodot, S., Forster, B., Pagès, L., Price, A., Tuberosa, R., Draye, X., 2007. Root system architecture: opportunities and constraints for genetic improvement of crops. Trends in Plant Science 12, 474–481. https://doi.org/10.1016/j.tplants.2007.08.012 Lynch, J. 1995. « Root Architecture and Plant Productivity ». Plant Physiology 109 (1): 7-13. https://doi.org/10.1104/pp.109.1.7. Thaon, P., 2017. Genetic analysis of wheat root architecture in aeroponics. Tuberosa, R., Sanguineti, M.C., Landi, P., Michela Giuliani, M., Salvi, S., Conti, S., 2002. Identification of QTLs for root characteristics in maize grown in hydroponics and analysis of their overlap with QTLs for grain yield in the field at two water regimes. Plant Mol Biol 48, 697–712. https://doi.org/10.1023/A:1014897607670 Wasson, A. P., R. A. Richards, R. Chatrath, S. C. Misra, S. V. Sai Prasad, G. J. Rebetzke, J. A. Kirkegaard, J. Christopher, et M. Watt. 2012. « Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops ». Journal of Experimental Botany 63 (9): 3485-98. https://doi.org/10.1093/jxb/ers111. Welcker, C., Sadok, W., Dignat, G., Renault, M., Salvi, S., Charcosset, A., Tardieu, F., 2011. A Common Genetic Determinism for Sensitivities to Soil Water Deficit and Evaporative Demand: Meta-Analysis of Quantitative Trait Loci and Introgression Lines of Maize. Plant Physiology 157, 718–729. https://doi.org/10.1104/pp.111.176479

Poster presented during the NSABS conference held in Gembloux Belgium on the 31th of January 2020.

Understanding drought tolerance mechanisms has never been so relevant, especially in view of the increasing diversity of water limited scenarios predicted by climate research. Classically, breeders target above ground traits to improve drought tolerance and a rather limited interest has been given to the root system architecture. Root traits should be considered because roots are key players of soil water extraction. In particular, special attention should be devoted to dynamic root traits in order to shift the focus towards a better understanding of drought resilience. Using time-lapse image sequences of whole root systems over three weeks, we captured dynamic information on root architecture of wheat seedlings growing in aeroponics. Three wheat diversity panels have been phenotyped: a MR-NAM bread wheat population (521 lines), a bread wheat diversity panel (250 varieties) and a durum wheat diversity panel (250 varieties). Data extraction, based on the identification and tracking of root tips in image sequences, has allowed the determination of the root growth rate, emergence, maximum length and apical diameter of primary and seminal roots. For the MR-NAM panel, a high heritability of seminal root emergence has been estimated, despite important environmental and genotype by environment variances. However, for the others seminal traits, heritability tended to be low. Efforts are ongoing to analyse lateral root traits, yet their extraction from images is challenging due the high density of lateral roots. A genome wide association study (GWAS) has been carried out with the MR-NAM population data and has led to the identification of three QTLs, related to seminal root growth rate and maximum root length. Phenotyping of the other panels are still ongoing and a meta-analysis will be conducted using GWAS results from the three panels. These experiments are part of the EU project SolACE (http://www.solace-eu.net). References: Burton, Amy L., James Johnson, Jillian Foerster, Meredith T. Hanlon, Shawn M. Kaeppler, Jonathan P. Lynch, et Kathleen M. Brown. 2015. « QTL Mapping and Phenotypic Variation of Root Anatomical Traits in Maize (Zea Mays L.) ». Theoretical and Applied Genetics 128 (1): 93-106. https://doi.org/10.1007/s00122-014-2414-8. de Dorlodot, S., 2007. Root system architecture: a genetic analysis in rice (PhD Thesis). Université catholique de Louvain. de Dorlodot, S., Forster, B., Pagès, L., Price, A., Tuberosa, R., Draye, X., 2007. Root system architecture: opportunities and constraints for genetic improvement of crops. Trends in Plant Science 12, 474–481. https://doi.org/10.1016/j.tplants.2007.08.012 Lynch, J. 1995. « Root Architecture and Plant Productivity ». Plant Physiology 109 (1): 7-13. https://doi.org/10.1104/pp.109.1.7. Thaon, P., 2017. Genetic analysis of wheat root architecture in aeroponics. Tuberosa, R., Sanguineti, M.C., Landi, P., Michela Giuliani, M., Salvi, S., Conti, S., 2002. Identification of QTLs for root characteristics in maize grown in hydroponics and analysis of their overlap with QTLs for grain yield in the field at two water regimes. Plant Mol Biol 48, 697–712. https://doi.org/10.1023/A:1014897607670 Wasson, A. P., R. A. Richards, R. Chatrath, S. C. Misra, S. V. Sai Prasad, G. J. Rebetzke, J. A. Kirkegaard, J. Christopher, et M. Watt. 2012. « Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops ». Journal of Experimental Botany 63 (9): 3485-98. https://doi.org/10.1093/jxb/ers111. Welcker, C., Sadok, W., Dignat, G., Renault, M., Salvi, S., Charcosset, A., Tardieu, F., 2011. A Common Genetic Determinism for Sensitivities to Soil Water Deficit and Evaporative Demand: Meta-Analysis of Quantitative Trait Loci and Introgression Lines of Maize. Plant Physiology 157, 718–729. https://doi.org/10.1104/pp.111.176479

Genetic Analysis of Dynamic Root Traits using Wheat Diversity Panels Clothilde Collet*, Patrick Thaon*, Karine Chenu, Jack Christopher, Xavier Draye. *These authors contributed equally to the work. Understanding drought tolerance mechanisms has never been so relevant, especially in view of the increasing diversity of water limited scenarios predicted by climate research. Classically, breeders target above ground traits to improve drought tolerance and a rather limited interest has been given to the root system architecture. Root traits should be considered because roots are key players of soil water extraction. In particular, special attention should be devoted to dynamic root traits in order to shift the focus towards a better understanding of drought resilience. Using time-lapse image sequences of whole root systems over three weeks, we captured dynamic information on root architecture of wheat seedlings growing in aeroponics. Three wheat diversity panels have been phenotyped: a MR-NAM bread wheat population (521 lines), a bread wheat diversity panel (250 varieties) and a durum wheat diversity panel (250 varieties). Data extraction, based on the identification and tracking of root tips in image sequences, has allowed the determination of the root growth rate, emergence, maximum length and apical diameter of primary and seminal roots. For the MR-NAM panel, a high heritability of seminal root emergence has been estimated, despite important environmental and genotype by environment variances. However, for the others seminal traits, heritability tended to be low. Efforts are ongoing to analyse lateral root traits, yet their extraction from images is challenging due the high density of lateral roots. A genome wide association study (GWAS) has been carried out with the MR-NAM population data and has led to the identification of three QTLs, related to seminal root growth rate and maximum root length. Phenotyping of the other panels are still ongoing and a meta-analysis will be conducted using GWAS results from the three panels. These experiments are part of the EU project SolACE (http://www.solace-eu.net). References: Burton, Amy L., James Johnson, Jillian Foerster, Meredith T. Hanlon, Shawn M. Kaeppler, Jonathan P. Lynch, et Kathleen M. Brown. 2015. « QTL Mapping and Phenotypic Variation of Root Anatomical Traits in Maize (Zea Mays L.) ». Theoretical and Applied Genetics 128 (1): 93‑106. https://doi.org/10.1007/s00122-014-2414-8. de Dorlodot, S., 2007. Root system architecture: a genetic analysis in rice (PhD Thesis). Université catholique de Louvain. de Dorlodot, S., Forster, B., Pagès, L., Price, A., Tuberosa, R., Draye, X., 2007. Root system architecture: opportunities and constraints for genetic improvement of crops. Trends in Plant Science 12, 474–481. https://doi.org/10.1016/j.tplants.2007.08.012 Lynch, J. 1995. « Root Architecture and Plant Productivity ». Plant Physiology 109 (1): 7‑13. https://doi.org/10.1104/pp.109.1.7. Thaon, P., 2017. Genetic analysis of wheat root architecture in aeroponics. Tuberosa, R., Sanguineti, M.C., Landi, P., Michela Giuliani, M., Salvi, S., Conti, S., 2002. Identification of QTLs for root characteristics in maize grown in hydroponics and analysis of their overlap with QTLs for grain yield in the field at two water regimes. Plant Mol Biol 48, 697–712. https://doi.org/10.1023/A:1014897607670 Wasson, A. P., R. A. Richards, R. Chatrath, S. C. Misra, S. V. Sai Prasad, G. J. Rebetzke, J. A. Kirkegaard, J. Christopher, et M. Watt. 2012. « Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops ». Journal of Experimental Botany 63 (9): 3485‑98. https://doi.org/10.1093/jxb/ers111. Welcker, C., Sadok, W., Dignat, G., Renault, M., Salvi, S., Charcosset, A., Tardieu, F., 2011. A Common Genetic Determinism for Sensitivities to Soil Water Deficit and Evaporative Demand: Meta-Analysis of Quantitative Trait Loci and Introgression Lines of Maize. Plant Physiology 157, 718–729. https://doi.org/10.1104/pp.111.176479

Phenotyping wheat seedling’s root angle variation to highlight correlations with water stress Clothilde Collet, Xavier Draye. An increasing diversity of water limited scenarios is predicted by climate research. Because roots determine soil-root conductance and water extraction[1], root traits have been proposed as a priority target to breed for drought tolerant yielding crops. There are many reports that the seminal root angle of cereal seedlings is a good predictor of several aspects of field root architecture[2], including deep root distribution[3],[4], which is considered as a positive adaptation to drought scenarios[5]. We have carried out an experiment under controlled conditions to analyse the genetic determinism of seminal root angles of wheat seedlings. Two diversity panels have been studied: a bread wheat diversity panel (250 varieties) and a durum wheat diversity panel (250 varieties). Seedlings (12 per genotype) were disposed at six different heights on a vertical germination paper plate whose moisture was maintained by capillary rise of water from the bottom of the plate. Daily pictures of the root systems have been captured during a 4-day long experiment and have been vectorized with the SmartRoot program. We observed a weak but significant correlation between the metric potential of water in the filter paper and the seedling seminal root angle. We also confirm that there is a very high broad-sense heritability for the root angle within each panel. This experiment is part of the EU project SolACE (http://www.solace-eu.net). [1] Xavier Draye et al., ‘Model-Assisted Integration of Physiological and Environmental Constraints Affecting the Dynamic and Spatial Patterns of Root Water Uptake from Soils’, Journal of Experimental Botany 61, no. 8 (May 2010): 2145–55, https://doi.org/10.1093/jxb/erq077. [2] Ahmad M. Manschadi et al., ‘The Role of Root Architectural Traits in Adaptation of Wheat to Water-Limited Environments’, Functional Plant Biology 33, no. 9 (22 September 2006): 823–37, https://doi.org/10.1071/FP06055; Manschadi et al. [3] A. Oyanagi, ‘Gravitropic Response Growth Angle and Vertical Distribution of Roots of Wheat (Triticum Aestivum L.)’, Plant and Soil165, no. 2 (1994): 323–26. [4] A. M. Manschadi et al., ‘Experimental and Modelling Studies of Drought‐adaptive Root Architectural Traits in Wheat (Triticum Aestivum L.)’, Plant Biosystems - An International Journal Dealing with All Aspects of Plant Biology 144, no. 2 (1 June 2010): 458–62, https://doi.org/10.1080/11263501003731805. [5] Ahmad M. Manschadi et al., ‘Genotypic Variation in Seedling Root Architectural Traits and Implications for Drought Adaptation in Wheat (Triticum Aestivum L.)’, Plant and Soil 303, no. 1 (1 February 2008): 115–29, https://doi.org/10.1007/s11104-007-9492-1.

Poster presented during the NSABS conference held in Gembloux Belgium on the 31th of January 2020.

Plants have evolved arrays of responses to abiotic constraints, many of which involve the root phenome. Presumably, these responses were shaped by natural selection to maximise adaptation and reproductive success. However, it is generally unclear whether this plasticity also contributes to improved agronomic performance of cultivated species under abiotic stress. In the context of the SolACE EU project, we monitored root growth and architecture of 250 bread wheat and 250 durum wheat genotypes in the 4PMI platform (rhizotubes) under combined low N and water and in the RootPhAir platform (aeroponics) under unconstrained conditions. Phenotypic plasticity in response to low N and water was estimated by comparing data from the two platforms. In parallel, conventional phenological and yield component variables were recorded for the same genotypes in replicated field trials involving control conditions vs combined low N and water. AMF colonisation data were also recorded on roots sampled in control conditions from one of the durum wheat trials. The genotypic effect (within each species) was significant for many variables and experiments. Root plasticity was predominant in the architectural data, as indicated by extremely low correlations between analogous variables in the two platforms. The root:shoot ratio was higher in 4PMI than in RootPhAir, which is consistent with the abiotic constraint present in the former. However, the genotypic variance for the root:shoot ratio was larger in RootPhAir than in 4PMI, as if the constraint in the latter was reducing the genotypic variability in root:shoot allocation. Field data were summarized by computing the rank of genotype responses to combined water and N deficits across the different trials, low ranks being assigned to generally sensitive genotypes. After assembling field and platform data, the sensitive genotypes in field trials tended to be those which have a low root allocation in RootPhAir (compared to 4PMI), while the tolerant genotypes in the field were those for which the root allocation in RootPhAir was close to that of 4PMI. Our interpretation is that the sensitive genotypes are able to reduce their root allocation when the root constraints are small, which makes them sensitive to soil-related constraints that would develop later during the crop cycle. Interestingly, the AMF data also points that the same genotypes are less keen to support the symbiotic association. Our results suggest that the ability to achieve a large root:shoot ratio is an important component of field crop tolerance to abiotic stress and call for reconsidering the value of architectural variables estimated in phenotyping platforms as direct predictors of crop tolerance.