Genotyping-by-sequencing (GBS) is a cost-efficient method which can be useful for SNP marker discovery in a population of interest. GBS is genome reduction sequencing method using restriction enzyme. The quality of DNA is a key factor which could have an influence in downstream analysis. However, there have not been many studies which investigated the impact of DNA degradation and the quality of the data on marker discovery. In this study, GBS data of 6 Hanwoo samples (H1~6) showing differing level of DNA degradation were compared. Re-sequencing pipeline was followed to investigate the impact of DNA degradation on marker discovery. As a result, we found that the quantity and quality of SNPs were not affected in the sample H5 and H6 with moderately degraded DNA. On the other hand, marker discovery was greatly affected in samples with severe DNA degradation (H3 and H4). The findings in this study support that GBS is a robust genotyping method towards moderate DNA degradation.

Pepper (Capsicum spp.) germplasm shows diverse phenotypic variations including fruit size, color, pungency, and many other horticultural traits. Traditional markers including SSR, AFLP, and RFLP have been used to construct genetic maps using biparental populations. However to assess the genetic diversity of large number of germplasm, a robust and rapid marker development and genotyping approach is needed. We used six pepper accessions including C. annuum, C. chinense, C. baccatum and C. frutescens and performed genotyping-by-sequencing (GBS). To select the most appropriate condition, eight different 2 bp selective nucleotides were used to make GBS libraries. Selective nucleotide ‘OO’ showed the largest number of reads in all samples, and 11,026 to 47,957 high-quality SNPs were called in six accessions. When C. annuum ‘CM334’ genome sequence was used as a reference, C. annuum showed the smallest number of SNPs, while C. baccatum which was known to be a different Capsicum clade showed the largest number of SNPs. Pepper core collection chosen to represent the genetic diversity of whole germplasm will be genotyped by high-density SNPs developed from GBS. We will perform genome-wide association study (GWAS) using genetic and phenotypic variation to identify the functional genetic loci controlling horticultural traits.

Clubroot is a devastating disease caused by Plasmodiophora brassicae and results in severe losses of yield and quality in Brassica crops including Brassica oleracea. Therefore, it is important to identify resistance gene for CR disease and apply it to breeding of Brassica crops. In this study, we applied genotyping-by-sequencing (GBS) technique to construct high resolution genetic map and mapping of clubroot resistance (CR) genes. A total of 18,187 GBS markers were identified between two parent lines resistant and susceptible to the disease, of which 4,103 markers were genotyped in all 78 F2 plants generated from crossing of both parent lines. The markers were clustered into nine linkage groups spanning 879.9 cM, generating high resolution genetic map enough to refine reported reference genome of cabbage. In addition, through QTL analysis using 78 F2:3 progenies and mapping based on the genetic map, two and single major QTLs were identified for resistance of race 2 and race 9 of P. brassicae, respectively. These QTLs did not show collinearity with CR loci found in Chinese cabbage (Brassica rapa) but roughly overlapped with CR loci identified in cabbage for resistance to race 4. Taken together, genetic map and QTLs obtained in this study will provide valuable information to improve reference genome and clubroot resistance in cabbage.