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United States Department of Agriculture

Agricultural Research Service


Location: Vegetable Research

2011 Annual Report

1a. Objectives (from AD-416)
Objective 1. Develop improved resistance to root-knot nematodes in pepper and watermelon. Objective 2. Identify and develop improved resistance to diseases in cucurbits, e.g. powdery mildew, downy mildew, Phytophthora blight, and watermelon vine decline. Objective 3. Elucidate virulence parameters of selected plant pathogen populations and develop integrated methodologies for managing cucurbit diseases.

1b. Approach (from AD-416)
Develop root-knot nematode-resistant sweet banana, sweet cherry, pimiento, and Cubanelle type peppers using backcross breeding procedures. Determine inheritance of resistance to root-knot nematodes (Meloidogyne incognita) in watermelon in greenhouse studies, and use techniques such as single sequence repeat (SSR) and sequence-related amplified polymorphism (SRAP) to develop molecular markers linked to root-knot nematode resistance genes in watermelon. Screen watermelon and melon germplasm for resistance to Phytophthora capsici and develop resistant germplasm. Screen bottle gourd (Lagenaria siceraria) plant introductions for resistance to powdery mildew in the greenhouse and develop resistant germplasm for use in rootstock breeding program. Screen watermelon plant introductions for resistance to watermelon vine decline, and evaluate strategies and develop integrated methodologies to manage watermelon vine decline in field tests. Identify prevalent races of powdery mildew using melon host differentials and determine their virulence on other selected cucurbit species in greenhouse and field studies. Determine genetic variability in the downy mildew pathogen (Pseudoperenospora cubensis) isolated from watermelon and cucumber using host differentials and molecular markers.

3. Progress Report
Single plant selections from Squash Vein Yellowing Virus (SqVYV) resistant wild watermelon germplasm lines were made to develop resistant watermelon germplasm. Wild melon (cantaloupe) germplasm lines were evaluated for resistance to crown rot caused by Phytophthora capsici and several resistant lines were identified. The core collection of watermelon Plant Introductions (PI), consisting of more than 200 PI, was evaluated for resistance to Phytophthora fruit rot and several lines with high levels of resistance were identified. Single plant selections from the most resistant lines were made to develop resistant watermelon germplasm. Wild bottle gourd germplasm lines were re-evaluated for resistance to Phytophthora crown rot and powdery mildew. Single plant selections were made to develop crown rot and powdery mildew resistant bottle gourd germplasm. Isolates of Phytophthora capsici from the southeast U.S. (Florida, Georgia, and South Carolina) were collected and will be used to study genetic variability of this fungus within specific fields and within regions of the southeast U.S. Insecticide treatments and resistant pollenizers were developed and evaluated for management of whitefly-transmitted SqVYV, which causes viral watermelon vine decline. Field studies were conducted to evaluate selected wild watermelon rootstocks for managing root-knot nematodes in grafted watermelon. Four watermelon rootstocks were moderately resistant to southern root-knot nematode and one rootstock produced significantly greater fruit yields than the other rootstocks. Studies on inheritance of resistance to southern root-knot nematode in watermelon were conducted. Pepper germplasm lines were screened and selected for resistance to northern root-knot nematode (Meloidogyne hapla) in greenhouse studies. Homozygous lines of sweet peppers were selected for resistance to southern root-knot nematode (Meloidogyne incognita). Fifteen cucurbit cultivars and wild germplasm lines were evaluated for their potential as rootstocks for managing southern root-knot nematode in grafted melon (cantaloupe) in field plots where soil had been fumigated with methyl bromide or not fumigated (control). Sweetpotato and southernpea (cowpea) germplasm lines were evaluated for resistance to southern root-knot nematodes.

4. Accomplishments
1. Phytophthora fruit rot of watermelon is an important and emerging disease in the southeastern U.S. This disease is caused by a fungus and can result in severe losses to watermelon production. There were no effective strategies to manage this important disease, so ARS scientists tested different fungicides (chemicals that can kill or reduce growth of the fungus) for managing Phytophthora fruit rot of watermelon. Of nine fungicides tested, Revus and Presidio were the most effective for controlling Phythophthora fruit rot. These fungicides are considered to be reduced risk pesticides and can be used safely by growers to manage Phytophthora fruit rot of watermelon.

Review Publications
Thies, J.A., Ariss, J.J., Hassell, R.L., Olsen, S., Kousik, C.S., Levi, A. 2010. Grafting for Management of Southern Root-knot Nematode, Meloidogyne Incognita, in Watermelon. Plant Disease. 94(10):1195-1199.

Kousik, C.S., Adams, M.L., Jester, W.R., Hassell, R., Harrison Jr, H.F., Holmes, G.J. 2011. Effect of Cultural Practices and Fungicides on Phytophthora Fruit Rot of Watermelon in the Carolinas. Crop Protection. 30:888-894.

Webster, C.G., Kousik, C.S., Roberts, P., Rosskopf, E.N., Turechek, W., Adkins, S.T. 2011. Cucurbit yellow stunting disorder virus detected in pigweed in Florida. Plant Disease. 95(3):360.

Last Modified: 2/23/2016
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