Supplemental red-light improves consistency of solid stem phenotype in solid-stem wheat varieties

Wheat stem sawfly (WSS) is a major pest of wheat with limited control options, causing substantial grain yield losses and reducing grain quality. Solid-stem genetic resistance has been the primary management strategy due to the lack of effective chemical or biological pest control options. However, the currently available solid-stem varieties often show inconsistent stem solidness across different environments. Because increased light intensity and longer day length are associated with stronger solid stem expression, we investigated the effect of supplemental red light (SL) in a greenhouse study comparing SL to standard greenhouse light (GL) across seven spring wheat varieties (Choteau, Conan, Dagmar, Duclair, Fortuna, Vida, along with Reeder, a hollow-stem variety). SL treatment enhanced solid-stem phenotypes in solid-stem varieties, with Duclair, Dagmar, and Choteau exhibiting consistent pith expression in both main stems and tillers, resulting in more uniform pith development. Transcriptomic analysis of first internode tissues from Reeder and Duclair under SL and GL conditions identified 55,997 differentially expressed genes (DEGs), with SL upregulating pathways related to cell division, phytochrome signaling, and photosynthesis. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichments analyses indicated that SL suppressed Programmed Cell Death (PCD) and promoted cytoskeletal remodeling, and energy reallocation, suggesting activation of signaling networks that support pith proliferation. These findings indicate that supplemental red light can stabilize the solid-stem phenotype through light-mediated gene regulation and may provide physiological and molecular insights to support breeding for improved WSS resistance and reduced lodging.