2006 Annual Report 1.What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? Why does it matter? This project addresses the general need for novel biologically based weed management strategies in two parts. Part A focuses on development of microbial biological control agents (NP 304 Component IX, Biological Control of Weeds), while Part B addresses the development of ecologically based weed management (NP 304 Component X, Weed Management Systems). Part A is designed to develop microbial herbicides to control important agricultural and invasive weeds, with an emphasis on the invasive perennial weed, Cirsium arvense (L.) Scop. (Canada thistle). A world collection of Pseudomanas syringae pv. tagetis will be screened for biological activity on several genotypes of C. arvense and for pathogenicity on a range of related non-host plants, plants typically found in areas where the biological control would be used, and crop plants. Efforts will be undertaken to enhance the biological activity of selected strains using molecular techniques to introduce genes for phytotoxin production, such as phaseolotoxin, tabtoxin, and caronatine. Non-toxigenic and toxin regulator mutants of P. syringae pv. tagetis will be developed and their biological activity compared to the wild-type strain to determine the role of tagetitoxin in the disease process. The genetic characterization of Aceria anthocoptes, the Canada thistle rust mite, will be conducted. Based on genetic differences identified, a DNA-based technique will be used to determine the natural distribution and host specificity of A. anthocoptes. Part B identifies ecologically based weed management strategies for sustainable and organic production systems. A combination of descriptive research to define the impact of long-term cropping systems and component research to identify superior crop cultivars and cover crop management systems will be used to determine improved weed management systems. The resources of three long-term cropping systems experiments will be used to explore the influence of conventional and organic cropping systems on weed population dynamics. This research will define weed population trajectories, community structure, and competitiveness over the 10 to 25 years these experiments have been in operation and will provide insight into the most effective systems and rotational phases for controlling weeds. Unique tall growing soybean germplasm that has been developed at Beltsville will provide an opportunity to test the role of the tall growth trait on the competitiveness of soybeans with weeds. Finally, the influence of cover crop residue decomposition and its interactions with soil properties and seed depth on weed seedling recruitment will be determined. This information will allow the design of improved cover crop and tillage management approaches that could permit the development of viable reduced-tillage organic cropping systems, currently an elusive goal. 2.List by year the currently approved milestones (indicators of research progress) Year 1 (FY 2006) 1. Strains of P. syringae pv. tagetis will be genetically characterized. 2. P. syrinage pv. tagetis will be modified with self-replicating plasmids containing phytotoxin-production genes and phytotoxin production by the resulting transformants will be evaluated. 3. Identify genes involved in the production of tagetitoxin, a phytotoxin produced by the biological control agent P.syringae pv. tagetis. 4. Analysis of basic agronomic data from the long-term “Demo” site will be completed. 5. Evaluation of the weed suppressive ability of soybean germplasm will be completed. 6. Initiate experiments to determine residue and soil factors that influence the recruitment of weed seedlings. Year 2 (FY 2007) 1. The efficacy of various P.syringae pv. tagetis strains will be determined. 2. Non-toxigenic mutants of P. syringae pv. tagetis will be developed/selected. 3. The genetic characterization of Aceria mites will be completed. 4. A PCR protocol to distinguish A. anthocoptes from other Aceria mites will be developed. 5. A decision will be made whether further study of soybean cultivars and/or traits is warranted. Year 3 (FY 2008) 1. The host range of the most efficacious strain of P. syringae pv. tagetis identified in studies from the previous year will be determined. 2. Studies on the epidemiology of P. syringae pv. tagetis in populations of Canada thistle will be conducted. 3. The natural host range of A. anthocoptes will be determined. 4. The efficacy of bacterial biological control agents of weeds modified with phytotoxin production genes will be evaluated. 5. The role of tagetitoxin in the biological activity of P. syringae pv. tagetis will be determined. 6. Analysis of weed seedbank population trajectories and community dynamics at the Demo” site and relationship to similar data at the long-term “FSP” and “FST” sites will be completed. Year 4 (FY 2009) 1. Studies on the epidemiology of P. syringae pv. tagetis in populations of Canada thistle will be conducted. 2. Complete experiments to determine residue and soil factors that influence the recruitment of weed seedlings. 4a.List the single most significant research accomplishment during FY 2006. Genetic and chemical characterization of a new bacterial pathogen of Canada thistle. A bacterium, Pseudomonas syringae strain CT99, that causes symptoms in Canada thistle that are similar to those caused by Pseuemonas syringae pv. tagetis was shown to be genetically different from all available Pseudomonas syringae pv. tagetis strains. Preliminary analysis suggests, however, that the phytotoxin produced by CT99 is chemically similar to tagetitoxin, a RNA polymerase inhibitor only reported to be produced by P. syrinage pv. tagetis. This newly discovered pathogen of Canada thistle needs further evaluation to determine its host range and efficacy as compared to P. syringae pv. tagetis or other P. syringae strains isolated from diseased Canada thistle. [Natonal Program 304, Component IX, Biological Control of Weeds, Problem A. Agent Discovery and Selection and Risk Assessment.] 4b.List other significant research accomplishment(s), if any. None. 4c.List significant activities that support special target populations. None. 4d.Progress report. Under objective B2, six cultivars of soybeans that ranged in height from tall to medium, that ranged in early growth rate from fast to slow, and that ranged in leaf shape from thin to wide were assessed for ability to suppress weeds. The trial was conducted in two fields with planted weed populations within row to achieve uniform weed pressure across each field and between fields. Although soybean cultivars exhibited the range of traits described above, there was no difference between cultivars in weed suppression. There also were small or no differences in the degree of cultivar growth and yield response to weed pressure. Results of this research demonstrated that the hypothesis for objective B2, that “tall stature and fast early growth will improve soybean competitiveness against annual weeds,” was false. Therefore, scarce resources will no longer be allocated to this objective but will be directed to objectives B1 and B3, instead. 5.Describe the major accomplishments to date and their predicted or actual impact. Synergistic enhancement of weed control with a cover crop-herbicide combination. During the past decade, researchers and farmers have been developing preventive systems for controlling weeds that minimize the use of interventions such as herbicides. Cover crops are an important tool for protecting soil, managing nutrients, and suppressing weeds in sustainable production systems, however, cover crop residue left on the surface of soil often provides incomplete or inconsistent weed control. This research explored the relationship between the amount of residue of the cover crop, hairy vetch, and the amount of the herbicide, metolachlor, applied to the soil surface on weed control. A synergistic relationship was demonstrated, meaning that by combining amounts of residue and herbicide that were marginally effective when used alone, a high degree of weed control was achieved. These results could open a new area of research that would target combinations of cover crops and low levels of selected phytotoxins to maximize weed control with minimal environmental impact (Component X - Weed Management Systems, Problem B. Integrated Weed Management in Cropland). Allelopathy makes short-term contribution to weed suppression by cover crops. Residue of leguminous cover crops such as hairy vetch contributes to integrated weed management and provides nitrogen for subsequent crops. Research was conducted to determine the role that toxins released by decomposing residue play in suppressing weeds, a process known as allelopathy. Results showed that hairy vetch residue that was allowed to decompose in the field or that was subjected to leaching in the laboratory was less suppressive of weed emergence and/or growth than was residue that was fresh. Results demonstrated that allelopathy contributes to weed suppression by the release of water-soluble phytotoxins from fresh hairy vetch residue for a relatively short time following cover crop kill until leaf tissue has decomposed (Component X - Weed Management Systems, Problem A. Cultural and Mechanical Control). 6.What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end-user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? The research results from the characterization of P. syringae strain CT99 should be available to other scientists in FY2007. Review Publications Teasdale, J.R., Pillai, P., Collins, R.T. 2006. Synergism between hairy vetch residue and low rates of metolachlor [abstract]. Weed Science Society of America Meeting Abstracts. 46:51. Teasdale, J.R., Abdul Baki, A.A., Park, Y.B., Rosecrance, R.C. 2006. The potential for allelopathy during decomposition of hairy vetch residue [abstract]. Proceedings of Northeastern Weed Science Society. 60:58.