Drought is a significant climatic factor that significantly affects the production of Chinese cabbage, a crop that is highly susceptible to drought stress. The development and cultivation of drought-tolerant varieties could be a viable strategy to minimize the damage caused by climate change and ensure stable production of Chinese cabbage. This requires the implementation of technologies for early evaluation and selection of a plethora of resources. In this study, we screened 100 varieties and breeding resources for drought tolerance under a water deficit treatment at the seedling stage. We also evaluated the growth response of Chinese cabbage varieties and breeding resources under water deficit treatment and selected drought-tolerant Chinese cabbage genotypes. We confirmed that the visual score for wilting, which evaluates the wilting response during the recovery process of Chinese cabbage seedlings through water deficit treatment and re-watering, can be used as an indicator for evaluating tolerance to drought stress. The visual score for wilting showed a high correlation with major traits representing drought tolerance. Our findings highlight the need for an integrated approach that considers various environmental conditions, varieties, and lines to select and develop drought-tolerant varieties. We selected ‘18-FH112-1’ and ‘18-FH112-1-2’ among others, and these germplasms will be useful resources for drought tolerance breeding. This study provides a foundation for future efforts to develop drought-tolerant Chinese cabbage varieties, thereby contributing to the stable production of this crucial crop.

Radish is a root vegetable crop, and many F₁ cultivars have been developed by exploiting heterosis. Considerable time and resources are required to test the performance and combining ability of F₁ cultivars and parental lines; therefore, economical methods to identify them are needed before field tests. This study was conducted to determine the minimum number of markers needed to identify cultivars and elite lines. PCR-based markers were applied to radish cultivars and elite lines and selected based on chromosomal location, polymorphic information content, and allele frequency. The power of selected marker sets to detect genetically similar cultivars or elite lines was confirmed using cultivars with high genetic similarity and elite lines with the same parents. Eleven markers successfully identified not only all 105 radish cultivars tested but also cultivars with high genetic similarity reported in previous studies. Fourteen markers, including the nine among 11 markers for cultivar identification, also successfully distinguished all 115 elite lines tested, including ones with the same parents and separated at F₂–F₆ generations. The markers developed for the identification of radish cultivars and elite lines require only 11 and 14 markers, respectively, and simple PCR and gel electrophoresis instruments. This method is very simple and can be easily applied to other crops.

The development of Chinese cabbage (Brassica rapa subsp. pekinensis) varieties that are resilient to climate change is becoming increasingly critical. Our study focused on developing stress-tolerant Chinese cabbage during the summer season to minimize the impacts of global climate change. We evaluated 52 Chinese cabbage accessions grown in the field during the late spring–summer season in Korea. Various phenotypic data of Chinese cabbage in adverse environments were collected from field data. In addition to field screening, we used a controlled-environment chamber to observe the direct impact of heat on young plants, particularly in the root area. A genome-wide association study was conducted using two sets of phenotypic data collected from both chamber and field studies and genotype data acquired from GBS analyses. A total of 57 SNPs distributed across all 10 B. rapa chromosomes were selected to be highly related to the target traits. Several candidate genes were annotated using the flanking sequences of these SNPs. The study revealed that most of the annotated genes seemed to be highly connected with the function of the heat stress response. Other genes were also found to be related to the environmental stress response and flowering. These candidate SNPs and genes can provide valuable tools for breeders to develop summer stress-tolerant Chinese cabbage varieties.

Bolting time is a critical trait that affects crop yield, adaptability, and overall productivity, making its regulation vital for agricultural success. In this study, we explored the genetic mechanisms controlling flowering time in radish (Raphanus sativus) via a combination of quantitative trait locus (QTL) analysis and genome-wide association study (GWAS). By developing an F₂ population from a cross between the relatively late-bolting variety ‘L432’ and the early-bolting variety ‘L285’, we identified 12 QTLs associated with bolting time. Furthermore, a GWAS performed on 60 East Asian radish accessions revealed 14 candidate genes potentially involved in flowering and bolting regulation. FLOWERING LOCUS C (FLC2) was the major candidate gene explaining the early and late bolting types. One locus was commonly detected from QTL and GWAS on chromosome 4, where CONSTANS-like (COL4) is located. To validate these findings, SNP markers were designed and applied to F₂ populations, revealing a correlation between marker presence and bolting phenotypes. These results offer valuable insights into the molecular control of bolting time in radish and identify candidate genes for use in marker-assisted breeding. These findings could enhance breeding efforts for optimizing bolting time in various radish markets.

The high yield of seeds can reduce the cost of seed production for parental lines, as well as F₁ cultivars in radish. The number of seeds per silique and silique length are two important traits among traits determining seed yield, but no study has been conducted on their quantitative trait loci (QTLs) in radish. A high-density linkage map was constructed, based on genotyping-by-sequencing (GBS) of the F₂ population, derived from two parental lines, significantly differed by the two traits, which were grown in a controlled environment to minimize the environmental effects. Using the map with 848 SNPs, three significant QTLs were identified, two and one of which were associated with the number of seeds per silique and silique length, respectively. Ortholog analysis was conducted with Arabidopsis thaliana genes, related to the number of seeds per silique, and revealed five radish putative candidate genes. These putative candidate genes appear to be related to ovule, embryo sac, embryo, pollen and seed development, as well as a double fertilization process. The method to pollinate the F₂ population, as well as preliminary QTLs and SNPs therein, can be helpful for future QTL studies to improve seed production in radish breeding programs.

The production of Kimchi cabbage (Brassica rapa L. ssp. pekinensis) is increasingly threatened by concurrent heat and drought stress, which induce physiological disorders and severe heading failure. In this study, we implemented a dual-environment screening strategy to identify robust indicators of heat resilience in an F₂ population. First, seedling-stage heat tolerance was evaluated in a controlled growth chamber using qualitative visual scoring (Scale 1–4) for shoot and root vigor. Second, the population was validated under summer field conditions in South Korea. Machine learning (ML) analysis revealed that the seedling-stage qualitative shoot-to-root (S/R) ratio was the most robust predictor of mature heat resilience, achieving a classification accuracy of 0.770 via SVM algorithms. The study also revealed a strong positive correlation (r = 0.71) between shoot apical meristem (SAM) wilting and localized calcium deficiency (tipburn). Individuals with severe SAM wilting were predominantly associated with severe tipburn and inner-leaf decay. Genome-wide association studies (GWAS) pinpointed the MIZU-KUSSEI 1-like (MIZ1-like) gene on Chromosome 2 as a primary candidate for S/R ratio regulation, potentially acting through the optimization of root hydrotropism. Our findings highlight that qualitative seedling-stage S/R ratio screening, integrated with ML models, serves as an efficient, breeder-friendly tool for early selection of climate-resilient B. rapa cultivars before field transplantation.