This study is to excavate embryo-related quantitative trait loci (QTL) with potential breeding value, to explore the genetic relationship between embryo and other agronomic traits in tetraploid wheat, and finally to aim at laying an important foundation for the fine mapping and breeding utilization of embryo-related traits in the future.

A total of 121 F₈ recombinant inbred lines (RIL) constructed by crossing tetraploid durum wheat (Ailanmai) and wild emmer wheat (LM001) were used. This RIL population was planted in five different environments including Chongzhou (2018-2020), Wenjiang (2020), and Ya'an (2020) in Sichuan Province for phenotypic evaluation of embryo length (EL), embryo width (EW), embryo length/embryo width (EL/EW), embryo length/kernel length (EL/KL), embryo width/kernel width (EW/KW), and embryo area (EA). QTL mapping was performed based on a genetic linkage map constructed based on the wheat 55K SNP.

The embryo size-related traits showed approximately normal distribution in the RIL population satisfying the genetic characteristics of quantitative traits. A total of 27 QTL for embryo size-related traits were detected in five environments over three years. Among them, seven ones controlling EL could contribute 7.75%-21.74% of phenotypic variation. Seven QTLs controlling EW could explain 7.67%-33.29% of phenotypic variation. Five stable and major QTLs (QEL.sicau-AM-3B, QEW.sicau-AM-2B, QEW/KW.sicau-AM-2B, QEL/EW.sicau- AM-2B-1 and QEA.sicau-AM-2B) were identified, and they explained 11.88%-18.99%, 21.77%-29.41%, 8.80%-24.92%, 12.79%- 25.69% and 10.47%-15.22% of phenotypic variation, respectively. In addition, four QTL-rich regions were identified in the embryo size-related loci mentioned above. The QTL controlling EL/KL and EL was located on chromosome 1B, that for EW, EL/EW, EW/KW, and EA was located on 2B, that controlling EL and EA was on 3B, and that controlling EL/EW and EW/KW was on 6B. Embryo size was significantly and positively correlated with kernel size. Further, the major QTL for EL, QEL.sicau-AM-3B was co-located with that for kernel length identified previously, but that for EW QEW.sicau-AM-2B was independent of that for kernel width. Four genes likely involved in regulation of embryo size were identified in intervals where major QTL were mapped.

Five stable and major QTLs were identified: QEL.sicau-AM-3B, QEW.sicau-AM-2B, QEW/KW.sicau-AM-2B, QEL/EW.sicau-AM-2B-1, QEA.sicau-AM-2B, among which QEW.sicau-AM-2B may be novel.