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.

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.