Breeding and genetics of resistance to major diseases in Cucurbita—A review.

<italic>Cucurbita</italic> crops, which include market types of pumpkin and squash, have unparalleled fruit variation and equally important economic value worldwide. Pumpkin and squash have versatile uses but are most popular in culinary, ornamental, snacking, and seed oil industries. The production of <italic>Cucurbita</italic> crops is hindered by diseases caused by fungal, oomycetes, and viral pathogens. Host resistance is an important component of integrated disease management for <italic>Cucurbita</italic> crops and is a major goal for plant breeders. This review addresses the major diseases of <italic>Cucurbita</italic>, including powdery mildew, downy mildew, <italic>Phytophthora</italic> rot, and aphid and whitefly transmitted viruses, with an emphasis on germplasm exploitation for the development of resistant cultivars. Resistance to powdery mildew derived from <italic>Cucurbita okeechobeensis</italic> subsp. martinezii (designated <italic>PM‐0)</italic> has been extensively deployed in commercial cultivars and was recently mapped on chromosomes 3 and 10 of <italic>Cucurbita moschata</italic> and <italic>Cucurbita pepo</italic>, respectively. Resistance to <italic>Phytophthora</italic> crown rot is present across several <italic>Cucurbita</italic> species, including <italic>Cucurbita lundelliana</italic>, <italic>C. okeechobeenesis</italic> subsp. <italic>okeechobeenesis</italic>, <italic>C. moschata</italic>, and <italic>C. pepo</italic>. Mapping studies have identified significant loci associated with <italic>Phytophthora</italic> crown rot resistance on chromosomes 4, 11, and 20 of <italic>C. moschata</italic> and chromosomes 4, 5, 8, 12, 13, 16, and 19 of <italic>C. pepo</italic>. Sources of resistance to aphid‐transmitted viruses exist in <italic>C. moschata</italic>, <italic>Cucurbita ficifolia</italic>, <italic>Cucurbita ecuadorensis</italic>, <italic>Cucurbita martinezii</italic>, <italic>C. ecuadorensi</italic>s, <italic>Cucurbita maxima</italic>, and <italic>Cucurbita foetidissima</italic>. The availability of DNA markers linked to resistance against zucchini yellow mosaic virus and papaya ringspot virus in <italic>C. moschata</italic> and <italic>C. pepo</italic> has facilitated marker‐assisted selection (MAS) in breeding programs. On the other hand, sources of resistance to tomato leaf curl New Delhi virus (ToLCNDV), a major whitefly‐transmitted virus in <italic>Cucurbita</italic>, have been identified in <italic>C. moschata</italic>, <italic>C. lundelliana</italic>, and <italic>C. okeechobeensis</italic>. A major locus conferring resistance to ToLCNDV in <italic>C. moschata</italic> was recently mapped on chromosome 8 enabling the application of MAS with a prediction accuracy of 94.3%. Overall, the continued discovery and application of genomic tools for resistance breeding in <italic>Cucurbita</italic> will accelerate the rate of genetic gain while reducing costs associated with phenotyping. [ABSTRACT FROM AUTHOR]