**5. Conclusions**

Peanut is one of the most important food/oil crops and improving the quality and yield potential of crops is an important challenge in most breeding programs. Our study demonstrated the feasibility of GWAS analysis using the core germplasm from diverse origins and high-density array chips. Five candidate markers with a significant correlation with the aspect ratio of peanut seeds were identified and lay a foundation for further research. The Arahy.HT9EWH, phosphoenolpyruvate carboxylase (PEPC) gene corresponding to the most significantly associated marker was a promising candidate gene that is involved in many metabolic pathways, including those involved in seed development processes. Therefore, the results of the present study provide valuable information and methods for the genetic and genomic study as well as molecular breeding programs in peanuts.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/2073-442 5/12/1/2/s1, Figure S1: ImageJ protocol, Figure S2: Δk values to confirm the number of populations, Figure S3: The estimation of LD decay, Table S1: Information on the 384 peanut accessions, Table S2: Information on the 384 peanut accessions seed aspect ratio, Table S3: A high-density SNP array 'Axiom\_Arachis' with 58K SNPs, Table S4: Information of the peanut genome from 58K SNP array chip, Table S5: Pairwise LD on chromosome Araip.B08, Table S6: List of genes in the significant region (chromosome Araip.B08) with annotations identified by *Arachis hypogaea* Tifrunner 1.0 reference, Table S7: Genome-wide association study (GWAS) (*p*-value < 0.001) of seed aspect ratio were constructed by different heterozygous filter methods.

**Author Contributions:** Conceptualization, T.-H.J.; methodology, T.-H.J. and H.S.; software, K.Z. and K.K.; formal analysis, K.Z. and K.K.; investigation, K.Z., D.K. and Y.-H.P.; resources, T.-H.J.; data curation, J.H. and K.-S.K.; writing—original draft preparation, K.Z. and K.-S.K.; writing—review and editing, B.-K.H., H.S., K.-S.K. and T.-H.J. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was carried out with the support of the "Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ013125022020)" Rural Development Administration, Republic of Korea.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable. **Data Availability Statement:** Please refer to suggested Data Availability Statements in section "MDPI Research Data Policies" at https://www.mdpi.com/ethics.

**Conflicts of Interest:** The authors declare no conflict of interest.
