Molecular Mechanisms Underlying Cucumber Resistance to Cucumber Green Mottle Mosaic Virus: From Host–Virus Interactions to Precision Breeding Strategies

Cucumber (Cucumis sativus L.) is an economically important vegetable crop cultivated worldwide, but its sustainable production is increasingly threatened by Cucumber green mottle mosaic virus (CGMMV). CGMMV is a positive-sense single-stranded RNA virus belonging to the genus Tobamovirus and represents a major constraint on cucurbit production because of its efficient seed transmission, mechanical spread, environmental persistence, and broad host range. Infection can cause leaf mosaic and mottling, growth suppression, and severe fruit symptoms, including internal discoloration, water-soaked tissues, and flesh deterioration, resulting in substantial losses in yield and commercial quality. Recent advances in cucumber genomics, resistance-germplasm screening, host–virus interaction studies, and molecular breeding have provided new opportunities for improving CGMMV resistance. However, progress remains constrained by the scarcity of well-characterized resistance donors, the limited functional validation of cucumber-specific resistance genes, isolate-dependent resistance responses, and the relatively low efficiency of cucumber transformation and genome editing. This review summarizes current knowledge of CGMMV infection processes, host susceptibility factors, antiviral defense pathways, resistance resources, and resistance-associated loci in cucumber and related cucurbits. Evidence is interpreted according to host species and the level of experimental validation. It further evaluates the potential of marker-assisted selection, genomic selection, genome editing, and RNA-based engineering and outlines an integrated framework for translating molecular findings into durable CGMMV-resistant cucumber cultivars.