*Corresponding Author C.S. Park: pcs89@jbnu.ac.kr

Understanding the genetic mechanisms underlying heading date is essential in wheat breeding to maximize productivity in different environments. As Korean wheat breeding programs have focused on developing early heading cultivars since the 1970s, most recent commercial cultivars already carry the alleles for early heading at the major genes such as VRN1 and PPD1.

This study aimed to identify new genetic factors influencing heading date by dissecting Quantitative Trait Loci (QTL) associated with days to heading date (DHD) in Korean Doubled Haploid lines. Ninety-four lines were evaluated for eight yield-related traits, including DHD, over three growing seasons (2017, 2018, and 2019).

A linkage map was constructed using 641 SNPs from 35K SNP Array, leading to the identification of three stable quantitative trait loci (QTLs) associated with days to heading date (QDhd.jbnu-3B, QDhd.jbnu-6B, and QDhd.jbnu-7D). Compared to the lines carrying the allele for late heading, those carrying the allele for early heading at QDhd.jbnu-3B, QDhd.jbnu-6B, and QDhd.jbnu-7D headed 3.1, 2.0, and 1.7 days earlier, respectively.

As the alleles for early heading at all three QTLs were associated with decreased kernels per spike, caution is required when deploying these alleles to minimize the negative impacts on yield. Nonetheless, the accumulation of alleles for early heading at the three QTLs resulted in an acceleration of heading date by approximately one week, indicating that these QTLs provide useful genetic resources for fine-tuning heading date.

We also developed a KASP marker for QDhd.jbnu-3B, the most impactful QTL for accelerating heading, and validated using 49 Korean cultivars. Cultivars with the early-heading allele headed 5.5 days earlier than those with the late-heading allele, suggesting that this KASP marker will be useful for further marker-assisted selection in Korea. This study provides valuable information for developing wheat cultivars with optimal heading dates.