Breeding Squash for Disease Resistance

hand pollinating squash flower

Image provided by L. Wessel-Beaver, University of Puerto Rico.

Cucurbita spp.

Powdery Mildew

Powdery mildew is a disease that affects all cucurbits and is important in squash. Resistance was introduced from the wild species, Cucurbita marintezii in C. moschata and C. pepo.

The resistance gene, Pm-0, is a single incompletely dominant gene that is commonly deployed in the heterozygous condition. We have defined this introgression and have found a candidate gene that we are effectively using for marker assisted selection for this resistance.

Numerous resistant cultivars are available in C. moschata and C. pepo.

Phytophthora blight

Phytophthora blight is found in infested soil and irrigation water and affects many vegetables. In squash and pumpkin it affects the root and crown of the plant and also the fruit that are particularly vulnerable if they lay upon infested soil. Resistance in the root and crown is derived from both the wild species C. martinezii and accessions of C. moschata.

Our breeding approach is to combine the resistances available in the vegetative portions of the plant with a compact bush architecture that would keep fruit upon raised beds and thus avoid exposure to pathogen infested soil. Concurrent genomics studies will facilitate the creation of tools for resistance breeding.

wilted plant

Symptoms of Phytophthora blight on squash include wilt. Image provided by Chris Smart, Cornell University.

Virus Diseases

Aphid transmitted viruses (Watermelon mosaic virus, Papaya ringspot virus, Zucchini yellow mosaic virus and Cucumber mosaic virus) are especially challenging for squash production in the Southeastern US. Resistance found in C. moschata and C. equadorensis was transferred into cultivated forms of C. moschata and C. pepo through conventional breeding approaches.

Some cultivars are available with resistance to these viruses individually and in combination. Transgenic squash with coat protein-derived resistance also exist.

Efforts are underway to create tools for MAS for resistance.

prsv on squash

Papaya ringspot virus on squash. Image provided by L. Wessel-Beaver, University of Puerto Rico.