2009 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 and identify molecular markers for root-knot nematode resistance genes in watermelon. Identify and develop improved resistance to Phytophthora capsici in watermelon and melon. Identify sources of resistance in watermelon plant introductions and develop management strategies for mature watermelon vine decline. Elucidate genetic variability in the downy mildew pathogen (Pseudoperenospora cubensis) isolated from watermelon and cucumber using conventional and molecular approaches.
Completed programs to develop a root-knot nematode resistant habanero pepper breeding line and a root-knot nematode resistant pimento pepper cultivar. Studies on inheritance of resistance to southern root-knot nematode in watermelon were conducted. Field studies were conducted to determine usefulness of different wild watermelon, squash hybrid, and bottle gourd rootstocks for managing root-knot nematodes in grafted watermelon. The wild watermelon lines were moderately resistant to southern root-knot nematode and may be useful as rootstocks for grafted watermelon. Two greenhouse studies to determine usefulness of pepper genotypes differing in resistance to root-knot nematode and Phytophthora capsici for managing root-knot nematode and Phytophthora blight in pepper were completed. Wild bottle gourd (Lagenaria siceraria) germplasm lines were evaluated for reaction to southern root-knot nematode (Meloidogyne incognita) in greenhouse studies. Over 300 wild melon (Cucumis melo) germplasm lines were evaluated for resistance to crown rot caused by Phytophthora capsici and a number of resistant lines were identified. Over 1,700 wild watermelon germplasm lines were evaluated for resistance to Phytophthora capsici and several lines were identified as sources of resistance to Phytophthora foliar blight and fruit rot. Numerous wild bottle gourd (Lagenaria siceraria) germplasm lines with moderate to high resistance to Phytophthora crown rot and foliar blight were identified. Strategies to manage white-fly transmitted viral watermelon vine decline were developed and tested. A combination of silver plastic mulch and insecticide treatments to reduce whitefly populations helped manage viral watermelon vine decline. Several commercial bottle gourd cultivars which are used as rootstocks for grafted watermelon were identified as resistant to crown rot caused by Phytophthora capsici. Techniques were developed to quantify levels of Phytophthora capsici infection in crown tissue samples from commercial rootstocks for grafted watermelon. Isolates of Phytophthora capsici and downy mildew (Pseudoperonospora cubensis) were collected from the southeast US (Florida, Georgia, and South Carolina) and will be used to study genetic variability in these fungi within specific fields and within the southeastern US. Variability in Phytophthora capsici strains isolated from watermelon and other cucurbits in the southeast US was observed. This report also documents research conducted under subordinate project no. 6659-22000-020-04N, a non-funded cooperative agreement between ARS and University of Florida.
Discovery of watermelon vine decline resistant germplasm. Watermelon vine decline is a new and emerging disease that has caused over $60 million in losses in watermelon producing regions of southwest and south central Florida. The disease causes complete collapse of the plant at or near harvest, resulting in poor quality fruit. ARS scientists in Charleston, SC, and Ft. Pierce, FL, tested many wild watermelon plants collected from different regions of the world for their reactions to the squash vein yellowing virus, which causes vine decline. Although none of the plants from the wild watermelon collection were completely immune to the virus, several accessions were moderately to highly resistant. This wild watermelon germplasm may be provide a source of resistance for the development of commercial watermelon varieties with resistance to vine decline.
Kousik, C.S., Adkins, S.T., Turechek, W., Roberts, P.D. 2009. Sources of Resistance in U.S. Plant Introductions to Watermelon Vine Decline Caused of Squash Vein Yellowing Virus. HortScience. 44:256-262.