Microspore culture is a key method for rapid development of genetically uniform lines. In this study, we aimed to identify the critical factors influencing the efficiency of microspore culture in Chinese cabbage (Brassica rapa), which is an important vegetable crop widely cultivated worldwide for its genetic diversity and nutritional value. To this end, we compared the efficiency of microspore embryogenesis across four different Chinese cabbage genotypes. We selected three accessions representing high, medium, and low efficiencies. Flower buds were harvested to examine pollen developmental stages using a light microscope. Unexpectedly, we found that the genotype with the highest efficiency (Wonkyo20044ho) had abnormally shaped microspores and pollen. In contrast, the genotype with the lowest efficiency (Wonkyo20039ho) had fine, normally shaped pollen. An additional experiment was conducted using the Wonkyo20044ho accession. Different bud sizes were harvested from this accession to observe differences in embryogenesis. The results showed that almost all pollen stages of this genotype were suitable for microspore culture. It can be assumed that the genotype is much more critical for microspore culture efficiency than the developmental stage of the pollen. Our results serve as a valuable reference for improved cabbage breeding methods.

Climate change caused by global warming, is predicted to have severe consequences for ecosystems and economic sectors. In the agricultural industry, it is predicted that there will be decreased crop yields resulting from shifting planting seasons, as well as higher temperature and water stress which significantly reduce crop productivity. Kimchi cabbage, a cold-loving plant, is particularly vulnerable to high-temperature stress which can lead to stunted growth, increased susceptibility to pests like soft rot, reduced yield, and lower quality that will negatively impact the Kimchi cabbage market. Kimchi cabbage can be cultivated in highland regions with low summer temperatures and reduced pest occurrence, but rising temperatures and water stress are expected to increase pest pressure, resulting in a rapid decrease in the potential cultivation area of Kimchi cabbage. Currently, research is being conducted around the world to identify physiological mechanisms of heat tolerance at the molecular level, selection of heat-tolerant material, and studies on cellular responses of plants under high-temperature conditions. Despite numerous studies on physiological and biochemical responses of Brassica crops to high temperatures, there is a need to develop heat-tolerant Kimchi cabbage cultivars that can adapt to rapidly changing climates, new strategies for pest control under high-temperature conditions, and mitigation measures to ensure stable cultivation and production.

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.

Kimchi cabbage (known as Chinese cabbage) is major vegetable in Korea. An inbred line of ‘Wonkyo20038ho’, was developed by the National Institute of Horticultural & Herbal Science, RDA in Republic of Korea. The microspore culture was carried out using ‘Chunhuigohangwang’ which was introduced from China in 2002. Among 3 DH inbred lines, ‘Wonkyo20038ho’ inbred line was finally selected after field exhibition in 2009. The horticultural traits of ‘Wonkyo20038ho’ inbred line; half-open head, white inner leaf colour, and dark green outer leaf colour. The average (for four years) head weight was 2025.3g, and head width and height were 15.8cm and 32.4cm, respectively. Head shape was narrow elliptic and degree of overlapping leaf was medium. Numbers of outer and internal leaves were 14.1 and 49.8, respectively. Harvest maturity was mid-late maturing type and average of seed yield for five years was 926 seeds. In addition, ‘Wonkyo20038ho’ inbred line is suitable for salad in that it possessed few trichome and narrow elliptic head shape.

Kimchi cabbage (known as Chinese cabbage) is one of the major vegetable in Korea. An inbred line ‘Wonkyo20042ho’, was developed by the National Institute of Horticultural & Herbal Science, RDA in South Korea. The first cross carried out using ‘Norang gwandong’ which had been introduced to Korea in 2007. During segrerating generations, bud pollination carried out using selected plants to fix genetic materials. ‘Wonkyo20042ho’ inbred line was finally selected by breeders from commercial companies at the field exhibition at 2011. The horticultural traits of ‘Wonkyo20042ho’ inbred line were as follows; half-open head, yellow inner leaf colour, and dark green outer leaf colour. The average head weight was 1899.2g, head width and height were 17.5cm and 27.9cm, respectively. Numbers of outer and internal leaves were 14.3 and 66.5, respectively. Harvest maturity was mid-late maturing type and average of seed yield for three years was 723 seeds. In addition, ‘Wonkyo20042ho’ inbred line showed resistance to clubroot disease (race 4 single spore isolation) and possessed thin leaves and small sized head.

Fusarium wilt, caused by a fungal pathogen Fusarium oxysporum f. sp. conglutinans (Foc), is a destructive disease of Brassica oleracea var. capitata. Currently, there are reports concerning molecular markers linked to Fusarium wilt disease resistance gene (FocBo1) in cabbage. In this study, we have studied a relationship between the FocBo1 gene and six cabbage breeding lines obtained from Asia Seed Company. The six cabbage breeding lines were evaluated resistance levels to Foc by combing of disease phenotypes and fungal biomass in planta. Of 6 breeding lines, KR-518 and OK-517 presented strong resistance and RK-P6-1, moderately resistance, whereas MT-624, JK-2, and HY-164, were susceptible to Foc. To define the correlation between the wilt disease resistance phenotype and the presence of resistance FocBo1 gene, we employed RT-PCR with MTK-C marker, which is known to be linked to FocBo1 resistant gene. The results exhibited inaccuracy in differentiating resistant and susceptible plants with genomic DNA samples, but it shows 100% correlation with cDNAs, indicating there is exceptional breeding line that contains FocBo1 gene in its genome with no expression. After cloning and sequencing the MTK-C product, a specific molecular marker, FocBo1-C, was developed which amplify a single, easily resolved band from cDNA of cabbage breeding lines with FocBo1 gene. Altogether, these results indicate that the three cabbage breeding lines in resistant category contain the resistance FocBo1 gene and moreover, the expression level of FocBo1 affect the degree of resistance of cabbage breeding lines, suggest the semidominant nature of FocBo1 gene in cabbage.