Identifying winter wheat ( <i>Triticum aestivum</i> L.) lines with group 1 herbicide tolerance

Abstract The management of herbicide‐tolerant weeds is a challenge for many winter wheat ( Triticum aestivum L.) producers. Implementing grass herbicide‐tolerant wheat cultivars, such as those under the CoAXium production system, may be an important tool. The objective of this experiment was to develop a screening method that identifies winter wheat lines with homozygous AADD genotypes and demonstrates tolerance to Aggressor AX herbicide. In this experiment, both an herbicide seed soak assay and molecular techniques were used to determine if lines contained the AXigen trait. Fourteen of the 20 populations phenotypically selected a different number of lines than were expected to be tolerant. Of those which were selected phenotypically for tolerance using the herbicide seed soak assay, only 27% of the lines were homozygous for the AADD genotype. While using the phenotypic screen appeared to select lines that were tolerant, few lines exhibited the two‐gene combination required for commercialization. Further research is needed to understand why the seed soak assay was selecting against two‐gene homozygous lines while allowing non‐homozygous lines to appear tolerant. Regardless, lines which were phenotypically screened first, and subsequently selected for homozygosity using molecular markers, demonstrated higher tolerance under field conditions compared to those only screened using markers. This two‐step process may be helpful in better selecting lines with high levels of herbicide tolerance rather than relying on molecular marker screening alone.