Genome-Wide Association Study Reveals Candidate Genes for Bacterial Angular Leaf Spot Resistance in Cucumber ( Cucumis sativus )

Bacterial angular leaf spot (BALS), induced by Pseudomonas amygdali pv. lachrymans, is among the most detrimental bacterial diseases affecting cucumber, leading to considerable yield reductions in recent years. Despite its significance, research on the genetic mapping of cucumber resistance to BALS remains scarce. This study evaluated the BALS resistance of 126 cucumber core germplasm accessions and performed a genome-wide association study (GWAS) using 1,642,740 single nucleotide polymorphisms. Two stable loci across two seasons, gBALS4.1 and gBALS6.1, were identified. Through gene annotations, sequence alignment, haplotype analysis, and qRT-PCR analysis, three candidate genes were identified as follows: CsaV3_4G024870 (late embryogenesis abundant protein-related/LEA protein-related), CsaV3_6G042860 (molybdenum cofactor sulfurase), and CsaV3_6G042910 (salicylic acid-binding protein 2-like). Among them, CsaV3_4G024870 and CsaV3_4G042910 were significantly upregulated after pathogen inoculation in BALS-resistance materials, while CsaV3_6G042860 was significantly upregulated in BALS-susceptible materials. This study elucidates the genetic mechanisms underlying BALS resistance in cucumber, thereby facilitating the breeding of cucumber varieties with enhanced BALS resistance.