Development and Preliminary Verification of Specific KASP Markers for Mango Resistance to Bacterial Angular Leaf Spot

Bacterial angular leaf spot, caused by Xanthomonas citri pv. mangiferaeindicae (Xcm), is an important disease that constrains mango production. Resistance-associated molecular markers can improve the efficiency of resistant germplasm screening and accelerate mango breeding; however, such markers remain limited for bacterial angular leaf spot. In this study, transcriptome and whole-genome resequencing data from the highly resistant cultivar ‘Renong No. 1’ and the highly susceptible cultivar ‘Keitt’ were reanalyzed to identify nonsynonymous single-nucleotide polymorphisms (SNPs) in candidate resistance-related genes. Among 86 candidate SNPs converted into Kompetitive Allele-Specific PCR (KASP) assays, 37 generated clear and stable genotype clusters in 25 mango accessions with known resistance phenotypes. SNP26 showed high consistency with the resistance phenotypes of these accessions and was subsequently used to genotype 322 mango germplasm accessions, which were separated into two genotype groups containing 34 and 288 accessions, respectively. Based on the SNP26 genotyping results, 72 accessions were selected for indoor fruit-puncture inoculation and classified into five resistance levels according to lesion development. SNP26 was located at position 1,299,510 on chromosome 15 within the coding region of HSP83A. The alleles were G in ‘Keitt’ and A in ‘Renong No. 1’, resulting in a leucine-to-valine substitution. Sanger sequencing confirmed the polymorphism at this locus. Following Xcm inoculation, HSP83A showed contrasting expression patterns between the two cultivars. Conserved domain and phylogenetic analyses indicated that HSP83A belongs to the HSP90/HtpG family and is closely related to homologous proteins in other plant species. These findings suggest that SNP26 is a promising resistance-associated marker for the preliminary identification of mango germplasm resistant to bacterial angular leaf spot and may facilitate marker-assisted selection in mango breeding.