Location: Vegetable Research2007 Annual Report
1a. Objectives (from AD-416)
Objective 1: Elucidate the etiology and epidemiology of Pepino mosaic virus on tomato and Pseudomonas syringae pv. maculicola on vegetable Brassicas to identify vulnerable areas (e.g., seed or alternative host) that provide biologically-based control opportunities. Objective 2: Identify and characterize genetic sources of disease resistance and facilitate the incorporation of these genes into enhanced germplasm of watermelon, tomato, and vegetable Brassicas. Objective 3: Identify and characterize new and existing bacteria antagonistc to phytopathogens and elucidate the factors that affect the potential efficacy of these biological control agents. Objective 4: Evaluate biologically-based control strategies to develop new and effective management practices against root-knot nematodes, pathogenic bacteria, and viruses.
1b. Approach (from AD-416)
Develop sensitive PCR-based detection methods and utilize these techniques to evaluate virus distribution in seed and plant tissues of tomato as well as other alternative crops or weed hosts. Develop molecular-based markers for identification and utilize these markers for environmental tracking of the vegetable Brassica leaf spotting bacterium Pseudomonas syringae pv. maculicola (Psm). Screen tomato germplasm for resistance to PepMV, evaluate the inheritance of resistance to Zucchini yellow mosaic virus (ZYMV) in watermelon, and develop molecular markers linked to the ZYMV resistance locus in watermelon. Screen germplasm from national collections of Brassica rapa and Brassica juncea for resistance to Pseudomonas syringae pv maculicola, and evaluate the genetics of resistance. Identify non-phytopathogenic pseudomonads that inhibit Pseudomonas syringae pv. maculicola and test for efficacy as biological control agents. Identify bacterial genes involved in bacterial-biocontrol colonization of plants using full-genome microarray analysis. Develop an effective seed treatment method for PepMV in tomato seed and generate virus-free materials of heirloom sweetpotato germplasm and breeding materials. Test effectiveness of the nematode-ovicidal bacterium Pseudomonas synxantha BG33R against root-knot nematode on melon in greenhouse and field assays.
3. Progress Report
A recent survey of PepMV in the U.S. and Canadian greenhouse tomatoes showed that PepMV is wide spread in all major greenhouse tomato production facilities and the prevalent strain of PepMV in North America is similar to the European tomato type. Furthermore, sources of resistance to PepMV strains were identified in wild tomato relative (Solanum habrochaites). Thermotherapy showed to be the most effective way to inactivate Pepino mosaic virus in tomato seed. In recent years, there is a growing trend to grow grafted watermelon in the U. S. Grafted watermelon not only is capable of combating soil-borne diseases but also in improving the quality of watermelon production. One major rootstock for watermelon is bottlegourd (Lagenaria siceraria). However, many of the current commercial bottlegourd cultivars are susceptible to virus infection. In this study, progress has been made in identifying several sources of virus resistance against Zucchini yellow mosaic virus (ZYMV) and Watermelon mosaic virus (WMV). These lines are under further single plant selection. The advanced lines were also evaluated under field conditions in South Carolina. A total of 60 heirloom sweetpotato accessions were evaluated for virus status with real-time polymerase chain reaction. Meristem shoot-tip culture technique was initiated to develop virus-free materials. Eight fields in the major Brassica growing region of South Carolina were surveyed for bacterial leaf spot. Collections of diseased tissues were made from more than 300 assorted leafy vegetable Brassica plants. Diseased tissues were processed and phytopathogenic bacterial strains were isolated and stored. These isolates have been characterized using microbiological, biochemical and DNA-based methodologies. Nearly 700 Brassica rapa and B. juncea Plant Introduction accessions were screened for resistance to the bacterial phytopathogen Pseudomonas syringae pv. maculicola. A number of accessions were found to possess resistance to the pathogen. Over 100 isolates of non-pathogenic pseudomonas were collected from several leaf spot affected fields in South Carolina. These isolates were tested for phytopathogenicity and characterized using DNA fingerprinting and biochemical analysis. These isolates will be tested in bioassays for inhibition of P. syringae pv. maculicola. Full genome, microarray analyses have been performed to identify genes involved in plant-root colonization. We looked at genetic responses of the biocontrol bacterium Pseudomonas putida as it colonized the roots of the model plant Arabidopsis thaliana. This initial study indicates that more than 100 genes are putatively being modulated by the interaction with the rhizosphere of Arabidopsis.
5. Significant Activities that Support Special Target Populations