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ARS Home » Southeast Area » Charleston, South Carolina » Vegetable Research » Research » Publications at this Location » Publication #358884

Research Project: Biology, Etiology and Host Resistance in Vegetable Crops to Diseases and Nematodes

Location: Vegetable Research

Title: Developing sources of resistance in Winter Squash (Cucurbita moschata) to Crown and Root Rot caused by Phytophthora capsici

item Kousik, Chandrasekar - Shaker
item Ikerd, Jennifer
item MANDAL, MIHIR - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/20/2018
Publication Date: 12/4/2018
Citation: Kousik, C.S., Ikerd, J.L., Mandal, M.K. 2018. Developing Sources of Resistance in Winter Squash (Cucurbita moschata) to Crown and Root Rot caused by Phytophthora capsici. Proceedings of the 2nd International Soiborne Oomycete conference, Page 39.

Interpretive Summary:

Technical Abstract: The oomycete plant pathogen Phytophthora capsici is a major factor limiting production of many vegetable crops throughout the USA. Diseases caused by P. capsici are particularly severe in southeastern USA, where conditions favorable for disease development are prevalent during the vegetable growing season year after year. Winter and crook neck squash (Cucurbita moschata) are important vegetable crops grown and consumed in most states in the USA. Among C. moschata, butternut type squash are the most popular and widely used across USA and other countries especially in Europe. Cucurbita moschata lines are also used to develop interspecific hybrid rootstocks with Cucurbita maxima for grafting watermelon in parts of Asia. In our previous studies it was observed that most commercially available C. moschata varieties and rootstocks were highly susceptible to crown and root rot caused by P. capsici. Watermelon grafting is becoming popular in the USA and rootstocks with resistance to P. capsici would be desirable. As part of an USDA, NIFA SCRI grant, we evaluated all the available plant introductions (PIs) of C. moschata (319 PIs) for resistance to P. capsici. Each PI was seeded in 6.3 cm square pots and had two replications with 4 plants per replication. The experiment was repeated twice. For inoculation, four-week-old plants were inoculated with 1 ml of 104 zoospore/ml suspension of a P. capsici isolate from South Carolina (SC). Plants were rated for disease severity two and three weeks after inoculation using a 0-5 rating scale. Majority of the plants from the 319 PI succumbed to root and crown rot and were rated 5. Plants rated 0 or =1 were considered as resistant. Twelve potential new sources of resistance (e.g. Grif 935, Grif 1738, PI 438724, PI 438778, PI 442272, and PI 442280) to crown rot and root rot caused by the local SC isolate of P. capsici were identified. Variability in resistance reaction among plants within a PI was also observed, and not all plants were resistant. This indicated the need for selecting and advancing individual resistant plants from germplasm collections to develop resistant sources. Further evaluation of S1 and S2 generation from the most resistant plants indicated that highly resistant plants could be selected from the 12 PI to develop lines for use in breeding programs. In a previous study done in Florida (FL), five sources of resistance to P. capsici (e.g. PI 176531, PI 458740) were identified in C. moschata by evaluating 119 accessions (Chavez et al., 2011, HortScience 46(4):536-540). In the current study additional new sources of resistance were identified. Interestingly, Grif 935, Grif 1738 and PI 442272 that were tolerant or resistant to the isolate from SC in the current evaluation were highly susceptible to a FL isolate (Chavez et al., 2011). We also selected resistant lines from these three PI and these selections were highly resistant compared to ‘Butterbush’ and ‘Waltham’ butternut squash, and the interspecific hybrid (C. moschata x C. maxima) rootstock ‘Carnivor’. These results also suggest the potential for existence of host specific races of P. capsici based on C. moschata. Our results suggests that once new sources of resistance are developed, they should be evaluated against isolates from other states prior to release for use in breeding programs. The 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.