New sources of resistance in winter squash (Cucurbita moschata) to phytophthora crown rot and their relationship to cultivated squash

Authors: Kousik, Chandrasekar - Shaker; VOGEL, G - Cornell University; Ikerd, Jennifer; MANDAL, MIHIR - Claflin University; MAZOUREK, M - Cornell University; SMART, C - Cornell University; Turechek, William

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2021
Publication Date: 9/13/2021
Citation: Kousik, C.S., Vogel, G.M., Ikerd, J.L., Mandal, M.K., Mazourek, M., Smart, C.D., Turechek, W. 2021. New sources of resistance in winter squash (Cucurbita moschata) to phytophthora crown rot and their relationship to cultivated squash. Plant Health Progress. 22:323-331. https://doi.org/10.1094/PHP-02-21-0047-FI.
DOI: https://doi.org/10.1094/PHP-02-21-0047-FI

Interpretive Summary: Butternut squash is an important vegetable crop grown and consumed in most states in the USA. Squash are also used as rootstocks for grafting watermelon and melon plants to help manage soil-borne diseases. In the southeastern USA it is difficult to grow squash and other vegetable crops as they are constantly infected by various diseases. One important disease causing serious yield loss in squash is Phytophthora crown rot. Currently commercial varieties resistant to Phytophthora crown rot are not available and hence growers use pesticides to manage this problem. USDA ARS researchers in Charleston, SC identified and developed several squash lines with resistance to Phytophthora crown rot. These new sources of resistance can be utilized for developing new crown and root rot resistant rootstocks for watermelon grafting and for developing resistant varieties for human consumption which will ultimately result in reduced pesticide use. The information will be useful for seed company breeders, private plant breeders, USDA and university researchers for developing squash varieties with resistance.

Technical Abstract: Butternut squash (Cucurbita moschata) is an important vegetable crop grown and consumed in most states in the USA. Cucurbita moschata lines and interspecific hybrids between Cucurbita species are also used as rootstocks for grafting watermelon and melon. However, currently most commercially available C. moschata squash varieties are highly susceptible to crown and root rot caused by the oomycete pathogen Phytophthora capsici, especially in the southeastern USA. All available plant introductions (PIs) of C. moschata (319 PIs) were evaluated for resistance to crown rot. Four-week-old plants were inoculated with 104 zoospores from a local South Carolina (SC) isolate of P. capsici. Plants were rated for disease severity three weeks after inoculation using a 0-5 rating scale. The majority of the C. moschata PIs were highly susceptible to crown rot in the first evaluation and were rated as 5. Reevaluation of the promising PIs identified several potential new sources of resistance (eg. Grif 935, PI 442272, PI 442264, PI 512142, PI 438724, PI 438778, PI 442280). Variability in resistance reaction among plants within a PI was also observed, and not all plants exhibited resistance. Further evaluation of S1 generation from the most resistant plants demonstrated that highly resistant plants could be selected from these PIs to develop lines for use in breeding programs. These new sources of resistance can be utilized for developing new crown and root rot resistant rootstocks for watermelon grafting and for developing resistant varieties for human consumption.