Doubled haploid (DH) technology is widely used in maize breeding because of its ability to produce 100% homozygous inbred lines within a short period of time. This efficiency has made DH technology an attractive tool for maize breeders, allowing its incorporation into breeding programs. This technology also facilitates advanced breeding techniques such as genome editing and the conversion of elite inbred lines into their cytoplasmic male sterility counterparts. The successful integration of DH technology into various maize breeding programs worldwide has spurred extensive research on the genetic basis and mechanisms underlying haploid induction, leading to the identification of key quantitative trait loci (QTL) aimed at improving efficiency and reducing costs. Additionally, new phenotypic markers are being explored for use along with the R1-nj marker to enhance the accuracy of haploid seed and plant identification. Efforts are underway to identify alternatives to colchicine, a toxic and carcinogenic compound commonly used for chromosome doubling. Nondestructive methods, such as nuclear magnetic resonance, Fourier transform Raman spectroscopy, and flow cytometry, are being developed to enable fast and accurate haploid identification and automate the process for large-scale breeding programs. As these advancements improve DH technology, the maize hybrid breeding paradigm is undergoing a substantial transformation. However, several challenges remain unaddressed.

Brassica juncea, a member of the Brassicaceae family commonly referred to as mustard, is an allotetraploid (AABB, 2n=36) resulting from interspecific hybridization between Brassica rapa (AA, 2n=20) and Brassica nigra (BB, 2n=16). In this study, microspores were cultured using F₁ hybrids between two selected B. juncea double haploid (DH) lines with high anthocyanin and glucosinolate contents in the maternal versus leafy paternity. The results of the microspore culture showed that the total number of cultured buds, obtained embryos, and embryos per bud were 2,010, 15,526, and 7.62, respectively. Colchicine was used to induce the amphidiploids (AABB). We found that 149 of the 218 regenerated plants (68.3%) were amphidoploid. Among them, 117 individuals underwent ripening and seed harvesting and were used for subsequent phenotype analysis. Leaf color, length, and other agricultural traits exhibited various patterns owing to the recombination of the parental allele. The glucosinolate (GSL) content ranged from a maximum of 29.27 μmol/g dry weight to a minimum of 6.39 μmol/g dry weight, exceeding the range of parental value. The composition of GSL was mainly aliphatic, with sinigrin accounting for approximately 89% of the total aliphatic GSL content. These DH lines and their respective unique phenotypic traits are crucial for crop breeding and are valuable resources for advancing functional genomics and developing molecular markers in B. juncea.

Many studies concerning breeding maize varieties are in progress in Korea and other countries. Double haploid technology is widely used for the development of commercial maize varieties worldwide, and has also been utilized in Korea since its introduction by the Maize Research Institute, Gangwondo. We performed a study to improve the efficiency of selecting haploid maize seeds using fluorescence imaging. It was verified that anthocyanin produced by the expression of R1-nj gene can be detected by fluorescence imaging, and we developed a high-throughput method for discriminating between haploid and diploid seeds. Compared with discriminating with naked eye, this method reduced the time for discriminating haploid and diploid maize by 91.7% and increased selection accuracy by 16.8% for haploid and 2.2% for diploid maize. This method enabled the acquisition of more haploid seeds and improved the efficiency of breeding research by shortening the time involved.

Rice doubled haploid (DH) lines derived from crosses of the indica cultivar 93-11 and japonica line Milyang352 were used in genetic mapping and QTL analysis studies of days to heading (DTH), an important trait that controls rice yield and biomass. QTL mapping was conducted using the inclusive composite interval mapping method. We used 234 single-nucleotide polymorphic markers in the whole-genome region, including 100 KASP markers and 134 Fluidigm markers, to construct a genetic map. DH populations were raised in Milyang, Korea, over three different periods. Two major DTH QTLs, qDTH3-1 and qDTH7, were detected under natural conditions in Milyang, and explained 14.88%~24.56% and 24.20%~37.39% of the phenotypic variation, respectively, in 93-11×Milyang352 DH populations. During three different rice cultivation periods, qDTH3-1 and qDTH7 were repeatedly detected with significant logarithm of the odds scores and phenotypic variability explained. The findings of this study will make a valuable contribution to breeding high-yielding and early-maturing rice in Korea.

The
objective
of this study was to identify quantitative trait loci (QTL) of spike length by association analysis with 94 doubled haploid wheat lines derived from Keumkang and Olgeuru. Days to heading date, culm length, spike length, and kernels per spike were evaluated in 2017 and 2018 in upland conditions. Culm length and spike length were biased short culm length and spike length (skewness=0.2 and 1.5, respectively). Kernel number per spike was biased low kernel number per spike (skewness=0.8). A genetic map was constructed with 170 microsatellite marker loci. One QTL was detected for spike length. The QTL on chromosome 4A, qSL-1 was detected by Xwmc283 and Xbarc327 explained 44.3% of the phenotypic variation. The QTL was applied to validate the relationship between genotypes of QTL and 29 Korean wheat cultivars grown for nine years under upland conditions. Korean wheat cultivars were classified into 5 types based on the combination of the two SSR markers. In Korean wheat cultivars, genotype b at Xbarc327, which was homozygous to Keumkang, had a shorter spike length (7.48 cm) than genotype c, which was different from the genotypes of Keumkang and Olgeuru, (8.45 cm). The two Korean wheat cultivars with genotypes ac at Xwmc283 and Xbarc327 had longer spike length (8.45 cm) than genotypes ba and bb (<7.42 cm).

Kimchi cabbage (Chinese cabbage) is a very common Korean traditional vegetable, cultivated across 32,000 ha, which accounts for about 13% of the total vegetable cultivation area in Korea. Since 2010, frequent occurrences of extreme weather conditions caused a shortage of summer, winter, and autumn Kimchi cabbage. Therefore, the National Institute of Horticultural and Herbal Science (NIHHS) selected a haploid breeding method of microspore culture to develop inbred lines that show resistance under extremely low or high temperature for Kimchi cabbage production. ‘Wonkyo20051ho’ is a double-haploid (DH) inbred line developed using the microspore culture method. Eleven heat resistant parental plants were selected through summer cultivation of 37 resources collected in 2014. Microspore culture was efficient in regenerating four resources, from which 13 DH inbred lines were developed. After artificially inoculating ‘Seosan’ clubroot with low concentration inoculum, 7 inbred lines showing moderate resistance were selected. As a result of the autumn cultivation of 83 breeding plants, including 6 selected inbred lines, the ‘18-FH98’ inbred line forming tight heads with yellow inner leaf under low temperature was finally selected during the 2018 autumn field trial. The selected DH inbred line was named ‘Wonkyo20051ho’ and is expected to be a valuable breeding material possessing tolerance to low temperature and clubroot.

Anther culture is useful and significant tool for producing haploid or doubled haploid (DH) plants in crop breeding system. Androgenesis is the way of inducing haploid and DH plants from anther (immature pollen) or microspore culture. In vitro androgenesis is efficient technique for introducing complete homozygous lines in one generation, thus less time and expense could be necessary than conventional plant breeding. In maize, anther culture is important system for shortening the breeding cycle and enhancing selection efficiency. Anther culture technique is also applicable to various researches such as molecular genetics, genetic engineering, genomics, and plant biotechnology. We review the past and present studies on anther culture and provide useful information for future researches on androgenesis in maize. The combination of androgenesis with other techniques such as molecular breeding and biotechnology is producing a variety of variety of maize species. In addition, we suggest strategy to develop androgenesis technique adapted to Korean research environment.

A doubled haploid (DH) lines derived from the cross between high-yielding japonica rice cultivars ‘Deuraechan’ and ‘Boramchan’ was developed to increase diversity of panicle and yield-related traits and select high-yielding lines. Panicle and yield-related traits of DH population consisting of 163 lines and 13 selected high-yielding lines were analyzed using correlation, principal component, and path analysis. Among panicle-related traits, number of spikelets on secondary rachis-branches (SRBs) was more highly correlated with and had more positive effect on number of spikelets (NS) than number of spikelets on primary rachis-branches (PRBs) per panicle. In the DH population, NS had the most positive effect on yield, whereas panicle number per hill (PN) was in the selected lines. PN was significantly positive correlated with ratio of ripened grain (RGG) in both case. The enhancement of ripening and increase of total spikelets number by increasing PN had more effect on yield than increase of total spiekelts number by increasing NS in the selected lines. Among 13 lines, four lines, AC60, AC152, AC156, and AC161 showed higher yield than Deuraechan (481 kg/10a) and Boramchan (558 kg/10a). Deuraechan exhibited panicle-weight type with low tiller and heavy panicles and Boramchan was slightly panicle-number type with more PN and higher RGG. Selected high-yielding lines showed medium characteristics of parents with improved yield potential. These elite lines could be utilized to develop high-yielding japonica rice.

Doubled haploid (DH) system is an effective tool in improving breeding efficiency and has been widely applied in wheat breeding programs. Wheat x maize hybridization is used for the production of wheat DH because of its efficiency and ease of application. We carried out an experiment to investigate genotype effect of wheat (Triticum aestivum) and maize (Zea mays) on efficiency of wheat haploid production. In various wheat x maize crosses, ten wheat and seven maize genotypes were tested. Haploid embryos were rescued and cultured for plant regeneration. Average seed set, embryo formation and haploid regeneration of five wheat varieties in crosses with a pollinator cv. Gangdaok were about 75%, 19% and 8.4%, respectively. Their haploid regeneration ranged from 3.7~9.8% and cv. Jokyoung showed highest regeneration. Average seed set, embryo formation and haploid regeneration of seven maize genotypes in crosses with a parent cv. Jokyoung were about 78%, 18% and 9.6%, respectively. Their haploid regeneration ranged from 7.6~12.9% and cv. Kwangpyeongok showed highest regeneration followed by cvs. Gangdaok and Gangilok. Analysis of variance for seed set and embryo formation showed highly significant effects of wheat parents and maize pollinators, whereas their interaction effect was only significant for seed set. The effect of maize genotypes on these traits was greater than that of wheat genotypes. Consequently, cvs. Kwangpyeongok, Gangdaok and Gangilok were found to be better pollen donors among the genotypes tested in wheat x maize hybridization for wheat hybrid production.