Breeding melon (Cucumis melo) with resistance to powdery mildew and downy mildew

Melon (Cucumis melo L.) production is often restricted by a plethora of pests and diseases, including powdery mildew and downy mildew caused respectively by the fungal species Podosphaera xanthii/Golovinomyces orontii and oomycete species Pseudoperonospora cubensis. Many efforts have been directed on identification of resistant sources by screening (wild) melon germplasm. In the current review, we summarized such efforts from various publications of the last 50 plus years. Resistance to powdery mildew has been identified in 239 melon accessions and downy mildew resistance in 452 accessions of both C. melo and the wild relative species C. figarei. Among the resistance sources, C. melo var. cantalupensis accessions PMR 45, PMR 5, PMR 6, and WMR 29 as well as C. melo var. momordica accessions PI 124111, PI 124112, and PI 414723 have been considered as the most valuable germplasm because multiple resistance genes have been identified from these accessions and are widely used in melon resistance breeding. Further genetic mapping in a number of resistant sources has enabled identification of 25 dominant genes, two recessive genes and seven QTLs conferring powdery mildew resistance, as well as eight dominant genes and 11 QTLs for downy mildew resistances. Based on the reported sequences of associated markers, we anchored physically (many of) these genes and QTLs to chromosomes of the melon cv. DHL92 genome. In addition to presenting a comprehensive overview on powdery mildew and downy mildew resistance in (wild) melon germplasm, we suggest strategies aiming at breeding melon with durable and broad-spectrum resistance to pathogens and pests