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1. High throughput phenotyping of cross-sectional morphology to assess stalk lodging resistance

   https://doi.org/10.1186/s13007-021-00833-3  

   Oduntan, Yusuf A. ; Stubbs, Christopher J. ; Robertson, Daniel J. ( January 2022 , Plant Methods)

   Stalk lodging (mechanical failure of plant stems during windstorms) leads to global yield losses in cereal crops estimated to range from 5% to 25% annually. The cross-sectional morphology of plant stalks is a key determinant of stalk lodging resistance. However, previously developed techniques for quantifying cross-sectional morphology of plant stalks are relatively low-throughput, expensive and often require specialized equipment and expertise. There is need for a simple and cost-effective technique to quantify plant traits related to stalk lodging resistance in a high-throughput manner.

   A new phenotyping methodology was developed and applied to a range of plant samples including, maize (Zea mays), sorghum (Sorghum bicolor), wheat (Triticum aestivum), poison hemlock (Conium maculatum), and Arabidopsis (Arabis thaliana). The major diameter, minor diameter, rind thickness and number of vascular bundles were quantified for each of these plant types. Linear correlation analyses demonstrated strong agreement between the newly developed method and more time-consuming manual techniques (R² > 0.9). In addition, the new method was used to generate several specimen-specific finite element models of plant stalks. All the models compiled without issue and were successfully imported into finite element software for analysis. All the models demonstrated reasonable and stable solutions when subjected to realistic applied loads.

   A rapid, low-cost, and user-friendly phenotyping methodology was developed to quantify two-dimensional plant cross-sections. The methodology offers reduced sample preparation time and cost as compared to previously developed techniques. The new methodology employs a stereoscope and a semi-automated image processing algorithm. The algorithm can be used to produce specimen-specific, dimensionally accurate computational models (including finite element models) of plant stalks.

    

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2. A Parameterised Model of Maize Stem Cross-sectional Morphology

   Ottesen, Michael A ; Larson, Ryan A. ; Stubbs, Christopher J ; Cook, Douglas D ( April 2022 , Biosystems engineering)

   Stalk lodging, or failure of the stalk structure, is a serious problem in the production of maize (corn). Addressing this problem requires an understanding of the parameters that influence lodging resistance. Computational modelling is a powerful tool for this purpose, but current modelling methods have limited throughput and do not provide the ability to modify individual geometric features. A parameterised model of the maize stalk has the potential to overcome these limitations. The purposes of this study were to (a) develop a parameterised model of the maize stalk cross-section that could accurately simulate the physical response of multiple loading cases, and (b) use this model to rigorously investigate the relationships between cross-sectional morphology and predictive model accuracy. Principal component analysis was utilised to reveal underlying geometric patterns which were used as parameters in a cross-sectional model. A series of approximated cross-sections was created that represented various levels of geometric fidelity. The true and approximated cross-sections were modelled in axial tension/compression, bending, transverse compression, and torsion. For each loading case, the predictive accuracy of each approximated model was calculated. A sensitivity study was also performed to quantify the influence of individual parameters. The simplest model, an elliptical cross-section consisting of just three parameters: major diameter, minor diameter, and rind thickness, accurately predicted the structural stiffness of all four loading cases. The modelling approach used in this study model can be used to parameterise the maize cross-section to any desired level of geometric fidelity, and could be applied to other plant species. 

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3. Development and stochastic validation of a parameterized model of maize stalk flexure and buckling

   https://doi.org/10.1093/insilicoplants/diad010  

   Ottesen, Michael ; Carter, Joseph ; Hall, Ryan ; Liu, Nan-Wei ; Cook, Douglas D. ; Zhu, ed., Xin-Guang ( August 2023 , in silico Plants)

   Maize stalk lodging is the structural failure of the stalk prior to harvest and is a major problem for maize (corn) producers and plant breeders. To address this problem, it is critical to understand precisely how geometric and material parameters of the maize stalk influence stalk strength. Computational models could be a powerful tool in such investigations, but current methods of creating computational models are costly, time-consuming and, most importantly, do not provide parameterized control of the maize stalk parameters. The purpose of this study was to develop and validate a parameterized 3D model of the maize stalk. The parameterized model provides independent control over all aspects of the maize stalk geometry and material properties. The model accurately captures the shape of actual maize stalks and is predictive of maize stalk stiffness and strength. The model was validated using stochastic sampling of material properties to account for uncertainty in the values and influence of mechanical tissue properties. Results indicated that buckling is influenced by material properties to a greater extent that flexural stiffness. Finally, we demonstrate that this model can be used to create an unlimited number of synthetic stalks from within the parameter space. This model will enable the future implementation of parameter sweep studies, sensitivity analysis and optimization studies, and can be used to create computational models of maize stalks with any desired combination of geometric and material properties.

    

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4. Maize stalk stiffness and strength are primarily determined by morphological factors

   https://doi.org/10.1038/s41598-021-04114-w  

   Stubbs, Christopher J ; Larson, R ; Cook, Douglas D ( January 2022 , Scientific reports)

   The maize (Zea mays) stem is a biological structure that must balance both biotic and structural load bearing duties. These competing requirements are particularly relevant in the design of new bioenergy crops. Although increased stem digestibility is typically associated with a lower structural strength and higher propensity for lodging, with the right balance between structural and biological activities it may be possible to design crops that are high-yielding and have digestible biomass. This study investigates the hypothesis that geometric factors are much more influential in determining structural strength than tissue properties. To study these influences, both physical and in silico experiments were used. First, maize stems were tested in three-point bending. Specimen-specific finite element models were created based on x-ray computed tomography scans. Models were validated by comparison with experimental data. Sensitivity analyses were used to assess the influence of structural parameters such as geometric and material properties. As hypothesized, geometry was found to have a much stronger influence on structural stability than material properties. This information reinforces the notion that deficiencies in tissue strength could be offset by manipulation of stalk morphology, thus allowing the creation of stalks which are both resilient and digestible. 

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5. Assessing axial and temporal effects of the leaf sheath on the flexural stiffness of large‐grain stems

   https://doi.org/10.1002/csc2.20899  

   Hale, Jared ; Webb, Spencer ; Hale, Nathan ; Stubbs, Christopher ; Cook, Douglas ( February 2023 , Crop Science)

   The leaf sheath of many plants has been observed to influence both stiffness and ultimate strength. For example, the sheath has been observed to be closely related to “greensnap” (or “brittle‐snap”) failure ofZea mays. The goal of this study was to develop a method for assessing longitudinal and temporal patterns of sheath influence on flexural stiffness. This metric was chosen because it has been shown to be predictive of ultimate bending strength. A three‐point bending test method was developed for assessing the longitudinal and temporal influence of the sheath on flexural stiffness ofZea mays. Comparisons between pairs of tests at the same location (sheath present vs. absent) were performed. Four types of maize were tested. The sheath had a statistically significant influence on bending. Sheath influence appears to be closely related to maturity since both spatial and temporal patterns of influence mirror the sigmoidal maturation patterns previously observed in maize stalks. The paired nature of this method increases statistical significance and allows for multiple tests along the length of the stalk. Results indicate that the influence of the sheath changes over the life span of theZea maysin parallel with maturation patterns. However, further studies will be needed to confirm this hypothesis more broadly and to study additional issues such as heritability and the influence of genotype and environment on sheath effects. Due to the common architecture ofPoaceaplants, this method can be used to provide new insights on sheath influences of various species.

    

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