A Comprehensive Review of Bacterial Leaf Spot (Xanthomonas spp.) Host Resistance in Pepper (Capsicum spp.).

Bacterial leaf spot (BLS) is one of the most destructive diseases of pepper (Capsicum spp.) worldwide, causing significant yield and quality losses under warm and humid conditions. The disease is caused by multiple Xanthomonas species, whose rapid evolution continues to challenge effective management. This review synthesizes current knowledge on BLS in pepper, including pathogen taxonomy, global distribution, and the historical progression of disease research and resistance breeding. We summarize advances in the identification and deployment of resistance loci, including major race-specific genes, as well as recessive resistance genes and quantitative resistance sources, and highlight the development of molecular markers supporting resistance breeding programs. We further integrate findings from transcriptomic, proteomic, metabolomic, and microRNA (miRNA) studies to elucidate the multilayered defense responses of pepper to Xanthomonas infection. Collectively, these multi-omics approaches indicate that effective resistance is governed by coordinated regulation of defense signaling pathways (e.g., salicylic acid, jasmonic acid, and ethylene), activation of resistance genes (including Bs2, Bs3, and related loci such as bs5 and bs6) and defense-associated transcription factors (e.g., WRKY), differential accumulation of defense-related proteins involved in stress responses, and metabolic reprogramming involving secondary metabolites. Finally, we outline key knowledge gaps and future priorities for developing durable and broad-spectrum resistance to BLS in pepper.