ARS | Publication request: Effect of phytophthora capsici crown rot on watermelon rootstocks and grafts

Submitted to: Cucurbitaceae Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 5, 2010
Publication Date: November 14, 2010
Citation: Kousik, C.S., Donahoo, R., Hassell, R. Effect of phytophthora capsici crown rot on watermelon rootstocks and grafts. Cucurbitaceae 2010 Proceedings. C.S. Kousik and A. Levi (eds.)pp. 305-307. 2010 (Proceedings)

Technical Abstract: Crown and fruit rot caused by Phytophthora capsici is becoming an important and emerging disease of watermelon in the southeastern United States. In recent years, the practice of grafting seedless watermelons onto rootstocks belonging to other Cucurbitaceae genera is also gaining acceptance in our local production areas. Therefore we evaluated seventeen commercial rootstocks in a greenhouse for tolerance to crown rot by inoculating them with P. capsici zoospore suspensions in two separate tests. All the Cucurbita inter-specific rootstocks and watermelon checks we evaluated were extremely susceptible, whereas the Lagenaria hybrid rootstocks were tolerant. We also evaluated watermelon grafted on select resistant and susceptible rootstocks and obtained similar results. A diagnostic PCR assay confirmed infection of all grafted susceptible rootstocks. Even though the Lagenaria rootstocks were tolerant, some of the plants (13-31%) tested positive for presence of P. capsici in PCR based assays. However, the pathogen could only be isolated from a few plants (3-7%) on semi-selective media. Real-time Q-PCR assays indicated the presence of more P. capsici DNA in the crowns of grafted Cucurbita rootstocks compared to Lagenaria rootstocks. We are conducting similar trials with watermelon grafted on select susceptible and tolerant rootstocks in a P. capsici infested field.