Fruit development period (FDP), defined as the time between full bloom and maturity, varies greatly in peaches (Prunus persica L. Batsch). It is necessary to develop molecular markers associated with maturity date to extend the harvest season in new peach cultivars. We designed the 260 SSR primer set covering the entire genome of approximately 300 kb to 1 Mb based on P. persica cultivar ‘Mihong’ genome sequence. The SSR markers were used to survey the relationship between the parentages ‘Yumeyong’ and ‘Chiyomaru’ and their offspring cultivars ‘Mihong’, ‘Yumi’, ‘Misshong’ and ‘Soomee’. Male cultivar ‘Chiyomaru and its offspring cultivars ‘Mihong’, Yumi’, and ‘Misshong’ are early and middle maturity cultivars with FDP of 77, 76, 82, and 108 days, respectively, whereas female cultivar ‘Yumyeong’ and its offspring cultivar ‘Soomee’ are late maturity cultivars with FDP of 128 days. Three regions of SSR markers could distinguish between early, middle, and late maturity cultivars. In the early stages of breeding, these markers will be used for marker-assisted selection (MAS) in the parentages ‘Yumyeong’ and ‘Chiyomaru’ and their offspring cultivars.

This study aimed to develop an agarose gel-based multiplex PCR assay using sequence-tagged site (STS) and simple sequence repeat (SSR) markers that can differentiate Korean wheat cultivars. Forty-nine Korean wheat cultivars were primarily classified based on seed coat color into red (36) and white (13) groups. Red wheat cultivars were further differentiated by three multiplex PCRs using molecular markers for Ppo-A1/Vrn-D1a/Rht-B1b, Glu-A3ac/TaCwi-A1b/Lr34, and Glu-A1ac/Glu-B1b/KWSM003/TaSE96. Similarly, white wheat cultivars were further differentiated using two multiplex PCRs using the molecular markers for Ppo-A1/Vrn-D1a/Pina-D1a and Ppo-B1/Glu-B3h. A multiplex PCR assay using molecular markers for Glu-A1b/Glu-D1d/Wx-B1 was developed to differentiate four Korean wheat cultivars used as government certified seeds: Baekkang, Hwanggeumal, Keumkang, and Saekeumkang. A multiplex PCR assay using molecular markers for Glu-B3h and Pin-D1a was used for colored wheat cultivars, Arijinheuk, Ariheuk, and Chinese colored wheat. The multiplex PCR assays developed in this study can provide useful molecular tools for differentiating Korean wheat cultivars, developing wheat seed management systems, and guaranteeing wheat seeds in Korea.

Prunus persica “Mihong” cultivar is a domesticated white peach that was generated from the crossing between “Yumyeong” and “Chiyomaru” cultivars in the Republic of Korea in 1995. We launched “Mihong” genome sequencing in 2018 and “Mihong” reached to 200 scaffold and 241 Mb sequences using long-read sequencing and Hi-C technology. F₁ populations of ”Kawanakajima Hakuto,” “Mihong,” “Changhowon Hwangdo,” and “Yumi” were developed in NIHHS. These four cultivars were sequenced and assembled using the SOAPdenovo version 2.04. First, we surveyed the SSRs in “Mihong” assembly sequences and extracted the ±300 bp flanking sequences containing SSRs. Second, the assembly sequences of three cultivars were aligned and mapped against “Mihong” ±300 bp flanking sequences using BLASTn (version 2.2.29+). We anticipated the differential length in SSRs among the four cultivars. We sorted the primers with a standard deviation over 4.5 (STEV > 4.5) among the four cultivars. In addition, we surveyed the primers having difference in over 10 bp with “Kawanakajima Hakuto” and “Mihong” for polymorphic markers in the mapping population. All primer pairs were designed to generate amplicons of 150-200 bp in coating SSR regions using primer3 (version 3-2.2.3). We selected 260 SSR markers with a physical distance of average per 1 Mb. These SSR markers accounted for 74% polymorphism in the four genotypes. Finally, a F₁ population of “Kawanakajima Hakuto” and “Mihong” covered 884.5 cM with 465 SNPs and 86 SSRs and this genetic map matched correctly to the HI-C pseudomolecule of P. persica.

Wheat (Triticum aestivum) is one of the three major food crops, along with rice and corn, and is the second most consumed crop after rice in Korea. However, the domestic production of wheat is insufficient, and the self-sufficiency rate is recorded in single digits. As wheat has a large genome size of 17 Gbp, and contains many repeated nucleotide sequences, it is difficult to conduct breeding studies and genome-based breeding lags behind that of other crops. To overcome the above challenges, we constructed a wheat core collection using simple sequence repeat markers that are suitable for the domestic cultivation environment with excellent reproducibility. Genetic diversity and population structure were analyzed using a core collection. Agricultural traits were evaluated in the Korean wheat core collection. Single marker analysis was correlated with 21 agricultural traits to identify potential molecular markers. These results may be useful for wheat breeding programs in the precision breeding era.

Chrysanthemum morifolium Ramat. is one of the major flowering crop plants worldwide. However, domestic chrysanthemum markets have recently faced a downturn. To stimulate related industries, breeding technologies and efficient protection systems using molecular markers must be established. However, high cost and intensive efforts are required to develop useful molecular markers for the chrysanthemum as it is a polyploid crop with highly complex genome organization. Thus, the aim of this research was to develop expressed sequence tag-based simple sequence repeat (EST-SSR) markers, which are applicable to the chrysanthemum breeding program and cultivar protection, based on next-generation sequencing technology. From the RNAseq data of the standard chrysanthemum cultivars ‘Jungwoon’ and ‘Seinoisei,’ we identified 31,121 SSR loci and further retrieved 1,846 polymorphic SSRs. To test the marker efficiency of the 1,846 SSRs, we first chose 50 of the SSRs and designed primers by using the flanking sequences. It is noted that the nine EST_SSR markers show a single band-like amplicon, which can be exploited in various genetic studies. We proceeded to polymorphism tests for those SSRs with 56 chrysanthemum cultivars, confirming that the average polymorphism index content (PIC) was 0.69±0.058. Among those, we found that six SSRs were sufficient to specify the genetic identities of 55 chrysanthemum cultivars, which may be useful for protections of the related cultivars, as well as breeding programs, in the future.

High-density genetic linkage mapping is critical for undertaking marker-assisted selection and confirming quantitative trait loci, as well as helping to build pseudomolecules of genomes. We constructed a genetic map using 94 F₁ populations generated from the interspecific cross between Korean cultivar “Wonwhang” (Pyrus pyrifolia, NCBI BioSample SAMN05196235) and European cultivar “Bartlett” (Pyrus communis). We designed a total of 24,267 SSR markers based on the genome sequences of “Wonwhang” for this. To select the markers that are linked to the traits important in pear breeding programs, SSR-containing genomic sequences were subjected to nucleotide sequence homology searches, which resulted in 510 SSR markers with high similarity to genes encoding proteins with putative functions such as transcription factors, resistance proteins, flowering time, and regulatory genes. Of these, 70 markers showed polymorphisms in parents and segregating populations and were used to construct a genetic linkage map, together with the unpublished 579 SNPs obtained from genotyping by sequencing analysis. The genetic linkage map covered 3,784.2 cM and the average distance between adjacent markers was 5.8 cM. Seventy SSR markers were distributed across 17 chromosomes with more than one locus.

We collected 32 maize inbred lines from eastern cereal and oilseed research center in Canada to develop new maize varieties. We also evaluated genetic diversity, genetic relationships, and population structure using 35 SSR markers. A total of 269 alleles were revealed in 35 loci with an average of 7.69 and a range between 3 and 15 alleles per locus. The genetic diversity values varied from 0.176 to 0.889 with an average of 0.691. The polymorphic information content varied from 0.171 to 0.879 with an average of 0.659. Population structure analysis indicated that 32 Canadian maize inbred lines comprised four major groups and one admixed group based on a membership probability threshold of 0.80. The four major groups contained 13, 2, 5 and 2 maize inbred lines, respectively. From genetic relationships analysis, the all inbred lines were divided into three main groups at 26% genetic similarity. Group I included 22 inbred lines, and Group II included 9 inbred lines. Group III consist of only one inbred line. The results in this study would be useful for the improvement and development of new cultivars, planning crosses for hybrids or development of inbred line in maize breeding program

Chrysanthemum (Dendranthema grandiflourm Kitamura) is a member of the Asteraceae and one of the important horticultural crops. The
objective
of this study was to construct a DNA profile database for identification of chrysanthemum varieties using simple sequence repeat (SSR) markers. In order to select SSR markers for the variety identification, we screened 587 SSR primers using 20 varieties. Among them, 27 SSR markers showed polymorphism. We finally selected 14 SSR markers showing peak clearance, high polymorphism and reproducibility in 20 varieties. In conclusion, DNA profile database for 147 chrysanthemum varieties were constructed by 14 SSR markers. A total of 79 SSR alleles were detected and three to ten alleles were detected with an average of 5.6 alleles per locus. The polymorphism information content value ranged 0.287 ~ 0.785 with an average of 0.598. Genetic relationship revealed that genetic distance of 147 varieties ranged from 0.44 to 1.00. The 143 varieties among 147 varieties were distinguished by 14 SSR markers but the 2 varieties developed by mutation breeding and natural variation were not distinguished from original varieties. These constructed SSR profile database will be useful for the selection of similar varieties for candidate variety and for solving problem relating to seed dispute and infringement of plant breeder’s right.

Grain yield, agronomic traits, and correlation between genetic distance of 36 F₁ hybrids produced by half-diallel crosses using nine maize inbred lines were analyzed. In the analyses of F₁ hybrids and their mid-parent heterosis (MPH) for agronomic traits, grain yield showed highest MPH value of 156%. One-hundred kernel weight showed the lowest value of 7%. In addition, when genetic distance based on agronomic traits was estimated, parental inbred lines did not agree with their own pedigree. Therefore it had the limitation to estimate genetic distance using agronomic traits. In this study, 92 SSR markers were used to calculate genetic distance at DNA level. However we did not confirm their own pedigree of nine parental inbred lines. There was no correlation between grain yield and SSR markers. Therefore molecular marker selection was conducted in relation with grain yield by the step-by-step method using 92 SSR markers. The selected nine SSR markers showed a significant positive correlation (r²=0.703**) between grain yield and SSR markers. The correlations between the selected SSR markers and agronomic traits of ear length, ear width, plant height, and ear height were particularly showed positively correlated. The nine SSR markers selected in this study would help predicting heterosis and planning crosses for hybrids in maize breeding programs.

This study was conducted to construct a DNA marker database for 38 plum varieties collected in Korea using simple sequence repeat (SSR) markers. A set of 61 SSR primer pairs was tested to select polymorphic SSR markers between 8 varieties. Among the 61 primer pairs, 21 showed polymorphism, reproducibility and easy scoring. The genetic relationship between the 21 SSR markers and 38 varieties was analyzed. A total of 210 polymorphic amplified fragments were obtained with the 21 SSR markers. Three to seventeen SSR alleles were detected for each locus, with an average of 10.0 alleles per locus. Average polymorphism information content (PIC) was 0.758, with a range from 0.549 to 0.870. A total of 210 SSR marker loci were used to calculate Jaccard’s distance coefficients for cluster analysis by an unweighted pair-group method with arithmetical average (UPGMA). The genetic distance ranged from 0.06 to 1.00 in 38 varieties. Out of 38 plum varieties, 32 were identified using the 21 SSR markers. Therefore, these SSR markers may be employed to complement distinctness, uniformity, and stability (DUS) tests or as potential tools to solve seed disputes regarding plums.