Unveiling the phenotypic landscape of stalk lodging resistance in diverse maize hybrids

Context: Stalk lodging causes up to 43 % of yield losses in maize (Zea mays L.) worldwide, significantly worsening food and feed shortages. Stalk lodging resistance is a complex trait specified by several structural, material, and geometric phenotypes. However, the identity, relative contribution, and genetic tractability of these intermediate phenotypes remain unknown. Objective: The study is designed to identify and evaluate plant-, organ-, and tissue-level intermediate phenotypes associated with stalk lodging resistance following standardized phenotyping protocols and to understand the variation and genetic tractability of these intermediate phenotypes. Methods: We examined 16 diverse maize hybrids in two environments to identify and evaluate intermediate phenotypes associated with stalk flexural stiffness, a reliable indicator of stalk lodging resistance, at physiological maturity. Engineering-informed and machine learning models were employed to understand relationships among intermediate phenotypes and stalk flexural stiffness. Results: Stalk flexural stiffness showed significant genetic variation and high heritability (0.64) in the evaluated hybrids. Significant genetic variation and comparable heritability for the cross-sectional moment of inertia and Young's modulus indicated that geometric and material properties are under tight genetic control and play a combinatorial role in determining stalk lodging resistance. Among the twelve internode-level traits measured on the bottom and the ear internode, most traits exhibited significant genetic variation among hybrids, moderate to high heritability, and considerable effect of genotype × environment interaction. The marginal statistical model based on structural engineering beam theory revealed that 74–80 % of the phenotypic variation for flexural stiffness was explained by accounting for the major diameter, minor diameter, and rind thickness of the stalks. The machine learning model explained a relatively modest proportion (58–62 %) of the variation for flexural stiffness. Conclusions: Characterization of stalk and internode properties using standard phenotyping methods revealed tremendous variation for intermediate phenotypes underlying stalk lodging resistance. The intermediate phenotypes showed moderate to high heritability, indicating their genetic tractability for improving stalk lodging resistance. Stalk geometric and material properties showed complementarity in determining stalk flexural stiffness. Engineering-informed models outperformed machine learning approaches in explaining variation for flexural stiffness. Implications: Identification of genetically tractable intermediate phenotypes will boost efforts toward genetic improvement of stalk lodging resistance in maize. Discovering the genetic architecture of the intermediate traits will enhance our understanding of the biological underpinning of stalk lodging resistance.