Assessing genetic diversity, population structure, and linkage disequilibrium is important in identifying potential parental lines for breeding programs. In this study, we assessed the genetic and phenotypic variation of 174 normal maize (Zea mays) inbred lines and made association analyses with respect to nine agronomical traits, using 150 simple sequence repeats (SSR). From population structure analysis, the lines were divided into three groups. Association analysis was done with a mixed linear model and a general linear model. Twenty one marker-trait associations involving 19 SSR markers were observed using the mixed model, with a significance level of P<0.01. All of these associations, as well as 120 additional marker-trait associations involving 77 SSR markers, were observed with the general model. Two significant marker-trait associations (SMTAs) were detected at P ≤ 0.0001. In the mixed linear model, one locus was associated with water content, two loci were associated with 100-kernel weight, setted ear length, ear thickness and stem thickness; three loci were associated with ear height, four loci were associated with total kernel weight and five loci were associated with plant height. These results should prove useful to breeders in the selection of parental lines and markers.

Bacterial spot of tomato (Solanum lycopersicum L.) is caused by at least four species of Xanthomonas with multiple physiological races. In this study, we developed a mapping population for association analysis of bacterial spot resistance. For this population, six advanced breeding lines with distinct sources of resistance were first crossed in all combinations and their F1 hybrids were intercrossed. The 1,100 segregating progeny from these crosses were evaluated in the field against T1 strains. Based on this individual evaluation, we selected 5% of the most resistant and 5% of the most susceptible progeny for evaluation as plots in two subsequent replicate field trials inoculated with T1 and T3 strains. A total of 461 markers across 12 chromosomes were used for genotyping these selections. Of these markers, an optimized subset of 384 SNPs was derived from the 7,720 SNP Infinium array developed by the Solanaceae Coordinated Agricultural Project (SolCAP). For association analysis to detect known resistance loci and additional novel loci, we used the mixed models with correction for population structure, and found that accounting for kinship appeared to be sufficient. Detection of known loci was not improved by adding a correction for structure using either a Q matrix from model-based clustering or covariate matrix from Principal Component Analysis. Both single-point and haplotype analyses identified strong associations in the region of the genome known to carry Rx-3 (chromosome 5) and Rx-4/Xv3 (chromosome 11). Additional QTL associated with resistance were detected on chromosomes 1, 3, 4, 6 and 7 for T1 resistance and chromosomes 2, 4, and 6 for T3 resistance. Haplotype analysis improved our ability to trace the origin of positive alleles. These results demonstrate that both known and novel associations can be identified using complex breeding populations that have experienced directional selection.

본 연구는 강원도 농업기술원 옥수수연구소에서 튀김옥 수수 품종개발을 위하여 육성한 79개의 자식계통들에 대하 여 대표적인 분자마커인 SSR마커를 이용하여 집단구조 및 association mapping 분석을 실시하였다. 집단구조에 대한 분 석 결과에서 79개의 튀김옥수수 자식계통들은 groups I, II, III, IV, admixed group으로 구분되었다. 4개의 옥수수 자식 계통은 group I에 포함되었고, Group II는 총 17개의 자식계 통들이 포함되었다. 그리고 6개의 자식계통들은 Group III에 포함되었으며, 22개의 자식계통들은 Group IV에 포함되었 다. 그리고 admixed group에는 30개 옥수수 자식계통들이 포함되었다. 튀김옥수수 자식계통들에 대하여 50개 SSR 마 커와 10개의 양적 형질 사이에서 association mapping 분석 을 하였다. Q GLM 분석에서는 0.01의 유의수준에서 92개의 marker-trait association을 확인하였으며, 반면에 Q+K MLM 분석에서는 0.01의 유의수준에서 6개의 marker-trait association 을 확인되었다. 본 연구에서 79개의 튀김옥수수 자식계통들 에 대한 집단구조 및 association mapping 분석의 결과는 앞 으로 강원도농업기술원 옥수수연구소에서 튀김옥수수 품종개 발을 위한 계통 육성 및 교배조합 구성 등에 유용한 정보를 제공할 것으로 기대한다.

Our study is performed to confirm the level of genetic diversity and population structure with 80 maize inbred lines (40 waxy inbred lines and 40 flint inbred lines) and to explain the genetic basis of agronomic traits using an association mapping. The 200 SSR loci are confirmed a total of 1,610 alleles in total 80 maize inbred lines. The average number of alleles per locus was 8.05. The average GD was 0.72. The average PIC value was 0.68. The average MAF was 0.40. Population structure was revealed for K=2. Total 80 maize inbred lines were divided by groups I, II and admixed group. The 14 waxy inbred lines were assigned to group I. The 45 inbred lines include 5 waxy inbred lines and 40 flint inbred lines were contained to group II. The 21 waxy inbred lines were contained in the admixed group with lower than membership threshold 0.8. Association mapping between 200 SSR markers and 10 phenotypic traits of waxy/flint maize inbred lines were performed by Q GLM and Q+K MLM. In significant level at 0.01, 72 SSR markers were associated with 10 phenotypic traits using Q GLM. The 4 marker-trait association were detected in Q+K MLM. The results derived from this study will be used for designing efficient new maize breeding programs.

NGS costs are decreasing rapidly, and beneficial application of the technology to plant genomics seems inevitable. Trying to interpret the agriculturally important traits like yield is actively in progress all across the globe. However, the current stage of bio-informatic technology as applied to the interpretation of agricultural trait appears not yet at a level of maturity to justify widespread plant genome sequencing for user-friendly molecular breeding. It is necessary to construct dense mutation block (DMB) based molecular breeding system for selecting plants with optimal agricultural performance; as well as for identifying useful quantitative trait loci (QTLs). Firstly, we screened and selected DMBs-specific INDEL markers obtained from SNV density profiles using 42 genome sequences of Korean cultivar and public sequences of 24 japonica rice cultivars. Secondly, we analyzed the genetic similarity between 288 Korean cultivars using 113 DMB-specific INDEL markers, which could differentiate on agarose gel by PCR. And we are going to integrate 360 INDEL markers up to 30 per each chromosome. Finally, we selected 40 founder lines considering the importance of the breeding, the purpose of use, and plant ecotype. To construct rice nested association mapping population we crossed each founder lines with the pollen of Hwayoungbyeo which was most commonly used in korean rice breeding program. F2 seed multiplication and generation iteration are ongoing.