Genetic Insights and Molecular Breeding Approaches for Downy Mildew Resistance in Cucumber (Cucumis sativus L.): Current Progress and Future Prospects

Cucurbit downy mildew, caused by Pseudoperonospora cubensis, is a devastating disease in cucumbers that leads to significant yield losses in many cucurbit-growing regions worldwide. Developing resistant cucumber varieties is a sustainable approach to managing this disease, especially given the limitations of chemical control and the evolving nature of pathogens. This article reviews the genetic basis of downy mildew resistance in cucumbers, emphasizing key resistance (R) genes and quantitative trait loci (QTLs) that have been mapped. Recent advances in molecular breeding tools, including marker-assisted selection (MAS), genomic selection (GS), and CRISPR/Cas9 genome editing, have accelerated the development of resistant cultivars. This review also explores the role of transcriptomics, genomics, and other 'omics' technologies in unraveling the molecular mechanisms behind resistance and offers insights into the future of breeding strategies aimed at long-term disease management. Management strategies for cucurbit downy mildew are discussed, along with the potential impacts of climate change on the occurrence and severity of downy mildew, highlighting how changing environmental conditions may influence disease dynamics. Integrating these advanced genetic approaches with traditional breeding promises to accelerate the development of downy mildew-resistant cucumber varieties, contributing to the sustainability and resilience of cucumber production.