Waterlogging poses a major challenge to Welsh onion (Allium fistulosum L.) production, exacerbated by climate change-induced extreme weather. Unraveling the molecular mechanisms of waterlogging tolerance is essential for breeding resilient cultivars. Here, we compared two Welsh onion varieties: BJQC (tolerant) and YZDC (sensitive). Waterlogging treatment revealed that YZDC exhibited higher accumulation of reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂), superoxide ions (O₂^–·), and malondialdehyde (MDA), leading to increased mortality. In contrast, BJQC demonstrated enhanced waterlogging tolerance, which was attributed to its ability to upregulate flavonoid biosynthesis genes, resulting in higher flavonoid accumulation under waterlogging stress. Transcriptomic analysis identified that the activation of flavonoid pathway-related genes in BJQC was central to this response. In addition, genes associated with jasmonic acid and gibberellin signaling were activated. Weighted gene co-expression network analysis (WGCNA) revealed that WRKY31 and MATE likely played critical roles in regulating flavonoid biosynthesis under waterlogging conditions. Genome-wide association study (GWAS) results from natural populations further supported the significance of these genes in waterlogging tolerance. Our comprehensive multi-omics analysis, including phenotypic, physiological, transcriptomic, and genomic approaches, provided new insights into the molecular mechanisms underlying Welsh onion responses to waterlogging. These findings highlight WRKY31 and MATE as key candidates for improving waterlogging tolerance in crop breeding programs.

High-throughput genotyping tools can effectively promote molecular breeding in crops. In this study, genotyping by target sequencing (GBTS) system was utilized to develop a genome-wide liquid SNP chip for facilitating genetics and breeding in melon (Cucumis melo L.), a globally cultivated economically important horticultural crop. Based on over eight million SNPs derived from 823 representative melon accessions, 16K, 8K, 4K, 2K, 1K, 500, 250 and 125 informative SNPs were screened and evaluated for their polymorphisms, conservation of flanking sequences, and distributions. The set of 2K SNPs was found to be optimal for representing the maximum diversity with the lowest number of SNPs, and it was selected to develop the liquid chip, named “Melon2K”. Using Melon2K, more than 1500 SNPs were detected across 17 samples of five melon cultivars, and the phylogenetic relationships were clearly constructed. Within the same cultivar, genetic differences were also assessed between different samples. We evaluated the performance of Melon2K in genetic background selection during the breeding process, obtaining the introgression lines of interested trait with more than 97% genetic background of elite variety by only two rounds of backcrossing. These results suggest that Melon2K provides a cost-effective, efficient and reliable platform for genetic analysis and molecular breeding in melon.