Dissecting culm strength in wheat: anatomical, biochemical, and genetic insights into lodging tolerance

Lodging is a major constraint in wheat production, often resulting in substantial yield losses. Resistance to lodging is influenced by various morphological, biochemical, and anatomical traits of the stem, and the relative contribution of different stem parts, particularly individual internodes, to lodging tolerance remains unclear. In this study, key culm-related morphological internode length (IL), internode weight (IW), stem diameter (SD), culm wall thickness (CWT), pith diameter (PD), the stem diameter to culm wall thickness ratio (SD/CWT) and the internode length to internode weight ratio (IL/IW), biochemical (cellulose), and anatomical traits were evaluated across the first three internodes in diverse wheat genotypes. The results revealed that the second internode played the most critical role in lodging tolerance. Lodging-resistant genotypes presented higher PD, CWT, IW, and cellulose content in the second internode, whereas susceptible genotypes presented increased IL and IL/IW ratios. Anatomical analyses revealed that resistant genotypes possessed more vascular bundles, thicker sclerenchyma, well-developed parenchyma, and enhanced lignin deposition in the second internode, collectively contributing to superior mechanical stability. Furthermore, single-marker analysis using SSR markers revealed 12 significant loci associated with 16 culm strength traits, with Gwm337 and Wmc273 explaining the greatest percentage of the phenotypic variance (24.40% and 23.01%, respectively). These findings underscore the pivotal role of the second internode in lodging tolerance and provide valuable molecular markers to support marker-assisted breeding for enhanced culm strength in wheat.