An incomplete understanding of stalk strength and stalk lodging impedes efforts to improve maize (Zea mays L.) production. To develop a more complete understanding of stalk strength, the current study examined the effect of stalk morphology on stalk bending strength. A detailed geometric analysis was conducted on five varieties of dent corn sown at five planting densities in two replicates at each of two locations near Greenville, IA, in 2013. Stalks were imaged using high‐resolution X‐ray computed tomography, and morphological features of the stalk were quantified using customized computer code. After scanning, stalks were subjected to mechanical tests to determine stalk bending strength and rind penetration resistance. The section modulus of the stalk (a morphological quantity derived from engineering beam theory) was found to be highly predictive of stalk strength, and its predictions appear to be largely unaffected by common confounding factors such as hybrid and planting density. By assuming the stalk cross section to be a hollow ellipse, the section modulus of the stalk can be estimated using measurements of stalk diameter and rind thickness (which does not require computerized tomography scanning). The elliptical section modulus is highly predictive of stalk strength, does not appear to be confounded by experimental variables, and can be obtained using a pair of calipers. Thus, it demonstrates potential as a selective breeding index to improve lodging resistance. In the current study, the elliptical section modulus predicted stalk strength with four times the accuracy of rind penetration resistance (a more common method used in breeding studies).

Late‐season stalk lodging in maize (Zea mays L.) is a major agronomic problem that has far‐reaching economic ramifications. More rapid advances in lodging resistance could be achieved through development of selective breeding tools that are not confounded by environmental factors. It was hypothesized that measurements of stalk flexural stiffness (a mechanical measurement inspired by engineering beam theory) would be a stronger predictor of stalk strength than current technologies. Stalk flexural stiffness, rind penetration resistance and stalk bending strength measurements were acquired for five commercial varieties of dent corn grown at five planting densities and two locations. Correlation analyses revealed that stalk flexural stiffness predicted 81% of the variation in stalk strength, whereas rind penetration resistance only accounted for 18% of the variation in stalk strength. Strength predictions based on measurements of stalk flexural stiffness were not confounded by hybrid type, planting density, or planting location. Strength predictions based on rind penetration resistance were moderately to severely confounded by such factors. Results indicate that stalk flexural stiffness is a good predictor of stalk strength and that it may outperform rind penetration resistance as a selective breeding tool to improve lodging resistance of future varieties of maize.

Stalk lodging is essentially a structural failure. It was therefore hypothesized that application of structural and forensic engineering principles would provide novel insights into the problem of late‐season stalk lodging of maize (Zea mays L.). This study presents results from a structural engineering failure analysis of corn stalk lodging, involving detailed inspection and measurements of lodged stalks and a multidimensional imaging study to assess stalk architecture based on structural engineering principles. This work involved in‐field observation of >20 varieties of lodged corn stalk in eight international locations and detailed geometric analysis of four varieties. Analysis of collected data revealed very strong, yet previously unreported, patterns in corn stalk lodging. Corn stalks predominantly fail (break) by creasing, fall in the direction of the minor diameter of the cross section, and break within 4 cm of a node. These failure patterns, across a broad sampling of varieties and environments, suggest a consistent weakness in maize stalk architecture, indicating that a common solution might be identified to strengthen maize stalks. Structural engineering analysis of stalk architecture and morphology revealed that several geometric stress concentrators (features known from engineering theory to increase local stresses) occur in the predominant failure region of corn stalk. Identified stress concentrators include surface irregularities, sharp changes in diameter, and voids occurring in the stalk pith. Each of these stalk features persist across different international locations, environmental conditions, and hybrid varieties. These findings support the use of new selective breeding approaches that focus on stalk morphology and structural engineering analysis of corn stalk architecture to develop lodging resistant varieties of maize.

Background: During traditional acupuncture therapy, soft tissues attach to and wind around the acupuncture needle. To study this phenomenon in a controlled and quantitative setting, we performed acupuncture needling in vitro.

No abstract