Location: Crop Improvement and Protection Research2009 Annual Report
1a. Objectives (from AD-416)
Objective 1: Optimize delivery and evaluate performance of chemical, cultural, biological, and genetic alternatives to methyl bromide for crops/pathogen combinations currently benefiting from the use of methyl bromide. a. Evaluate alternative fumigants. b. Identify genes associated with pathogenicity of Verticillium dahliae based on a Verticillium comparative genomics study to support the development of alternative control procedures. c. Identify emerging diseases and their etiology and evaluate resistant germplasm for diseases of strawberry, lettuce, and vegetables. d. Evaluate the influence of crop rotation on pathogen populations and beneficial microbial community dynamics in the soil and severity of Verticillium wilt and other diseases. Develop tools to evaluate and understand the role of myxobacteria in agricultural and natural ecosystems in an effort to elucidate their potential for pathogen control. Objective 2: Develop molecular diagnostic tools for the identification of emerging diseases of vegetables and strawberries, and use these tools in the development of management strategies as alternatives to methyl bromide.
1b. Approach (from AD-416)
Develop integrated management approaches including crop rotation, biological control, selection of disease resistant varities, organic production, other biological practices, and combinations of biological practices with reduced concentrations of chemical fumigants to control diseases. Identifying useful commercial biological agents as well as new agents from the strawberry rhizosphere that will help to improve plant growth and disease management. Molecular tools will be developed for evaluation of the fficacy of pathogen management and modeling population dynamics of beneficial microbes. Replaces 5305-22000-009-00D(11/07).
3. Progress Report
Continued analyses of the genomes of V. dahliae and V. albo-atrum and comparison to other genomes have revealed sets of genes that are unique to V. dahliae. For additional in-depth analyses, a research proposal was written with 7 other researchers from the US and abroad and submitted to the competitive grants program of the US Agriculture and Food Research Initiative for functional genomics analyses of V. dahliae. Preliminary screens of insertional mutants of V. dahliae have identified two candidate mutant strains of V. dahliae that are potentially nonpathogenic on lettuce. We examined the expression of two defense-related genes of lettuce in response to fungal infection in an additional lettuce cultivar. The experiments revealed that both putative antifungal genes are upregulated in the susceptible interaction with V. dahliae, in leaf tissues. Results of independent differential screening also reveal that these same genes are expressed at higher levels in lettuce leaves infected with V. dahliae versus the non-inoculated control plants. The development of a PCR method in collaboration with the UC Davis to distinguish between two races of V. dahliae is ongoing, using published primer sequences. Our results indicate that this marker system may be useful for rapidly distinguishing between races of V. dahliae pathogenic on lettuce and tomato grown in California. The development of an assay for use in growth chambers that enables a rapid assessment of pathogenicity of V. dahliae on lettuce was completed. This technique employs the use of lettuce seedlings contained in tubes. This technique offers advantages over conventional assays in greenhouses for Verticillium wilt since it is contained, rapid, the environment is controlled, and reduces labor costs associated with lengthy greenhouse assays. We described six novel diseases from the Western US and made tentative identifications of the pathogens from four of the diseases. We also determined that epidemics of bacterial blight on parsley in California and Arizona since 2003 have been caused by two and possibly three different pathogens and are currently evaluating the breadth of the host range of these pathogens. We continue to monitor these emerging diseases. Rifampicin resistant variants of nine bacterial plant pathogens and environmental organisms (needed for myxobacterial enrichment studies) were generated. We are currently comparing these variants to the wild type strains for growth characteristics and virulence on plants. We concluded field trials that identified commercially available strawberry cultivars that are resistant to the pathogen causing Strawberry Blossom Blight. We have shown that the pathogen is similar but substantially different from a know plant pathogen, Pseudomonas marginalis and are concluding the identification. We have completed FAME analysis to measure changes in microbial communities in an experiment measuring the impact of 1 – 5 years vegetable rotation on organic strawberry production in collaboration with a scientist. Data analysis is in progress. We collaborated with ARS Scientists at two other locations in California and university researchers on
5. Significant Activities that Support Special Target Populations
• An ARS scientist mentored three students (2 minority and one woman) from Hartnell College and CSUMB (both minority serving institutions) through a grant funded internship program. • An ARS scientist mentored a former minority student intern in preparation graduate school application, a USDA graduate student proposal, and personally provided support and travel for this student to the American Phytopathological Society Meeting in Portland, OR. This student was accepted to the Plant Pathology Department at the University of Wisconsin and will begin a Ph.D. program this fall. • An ARS scientist organized and participated in 5 field trips or outreach activities by the USDA for Hartnell College or CSUMB classes or students. • An ARS scientist initiated a project in which our research station is “adopting” with four 5th grade classes at a local minority serving elementary school to provide science programming and field trips. • An ARS scientist organized USDA participation and participated in a Teacher Externship Day Thirty teachers from the Salinas valley attended. • An ARS scientist participated in WISE Women In Science Exploration of Hartnell Community College as a mentor and sponsor. • An ARS scientist provided additional outreach activities to classes or administrators from 2 additional elementary schools in Salinas. • An ARS scientist provided a field trip to the station for Girl Scout Troup 3197 and their parents. • An ARS scientist serves on the Joint Committee for Women in Plant Pathology and Cultural Diversity for APS • An ARS scientist organized and delivered one summer workshop for Salinas High School teachers at the USDA-ARS station in Salinas, CA. • An ARS scientist has been working with administrators and teachers at Spreckels Elementary School on their science curriculum.
Bull, C.T., De Boer, S.H., Denny, T.P., Firrao, G., Fischer-Le Saux, M., Saddler, G.S., Scortichini, M., Stead, D.E., Takikawa, Y. 2008. Demystifying the Nomenclature of Bacterial Plant Pathogens. Journal of Plant Pathology. 90:403-417.