Location: Foreign Disease-Weed Science Research2018 Annual Report
Objective 1: Develop biological control agents for invasive weeds (such as Russian thistle, Russian knapweed, common crupina, and invasive Rubus species) through the identification, isolation, efficacy testing, and host-specificity evaluation of candidate plant pathogens (such as Colletotrichum salsolae, Phoma exigua, and Ramularia crupinae). [NP304, Component 2, Problem Statement 2B3] Sub-objective 1A - Isolation and identification. Sub-objective 1B - Evaluation of pathogen efficacy. Sub-objective 1C - Evaluation of disease reaction among non-target and target species. Sub-objective 1D - Develop and submit a proposal for release that describes the importance of the target weed as a pest and the efficacy and safety of a candidate pathogen. Sub-objective 1E - Participate with cooperators in release and post-release monitoring of the pathogen (under permit from state and federal regulators). Objective 2: Develop methods to rapidly screen and identify plant pathogens that have a high probability of being useful, safe, and effective as biological control agents for high priority invasive weeds (such as Russian thistle, Russian knapweed, common Crupina, and invasive Rubus species), in that they have the desired properties of high virulence and pathogenicity to the target weed, yet are sufficiently host specific that they are not a threat to beneficial and native organisms (such as crop and rare plants). [NP304, Component 2, Problem Statement 2B3] Sub-objective 2A - Refine and improve statistical approaches to risk assessments that combine disease response data with quantitative plant relationship data based upon molecular characteristics. Sub-objective 2B - Refine and apply available protocols in microscopy, physiology, and bioinformatics to improve risk assessments and clarify results of tests in Objective 1, particularly concerning non-target plant species reactions.
Exotic pathogens will be collected from symptomatic target weeds in countries where they are native, evaluated for their potential using standard plant pathology methods, and identified using both classical morphological characters and molecular sequence data. The primary target weeds will be Canada thistle, Russian thistle, Russian knapweed, yellowstarthistle, and medusahead. Other targets include, but are not limited to: Carduus thistles, milk thistle, knapweeds, common crupina, whitetop, broadleaved pepperweed, invasive blackberry, swallow-worts, cheat grass, teasel, and field and hedge bindweed. Pathogens will be evaluated for the risk associated with intended release into ecosystems containing economically and ecologically important North American plant species. Risk will be evaluated, in quarantine, based on disease reaction of species related to the target weed from a test-plant list reviewed and modified according to recommendations of regulators at the USDA Animal and Plant Health Inspection Service. In evaluating disease reaction, protocols for improved risk assessment will be developed and used. These include an advanced statistical analysis that incorporates disease reaction data with genetic relatedness, from DNA sequences, of species on the test-plant list. Output from these analyses will be best linear unbiased predictors of the disease reaction of each species. Other protocols incorporating advancements in histology, microscopy, and genetics will also be used to improve understanding of risk and non-target plant disease responses. Pathogens determined to have an adequately narrow host range will be proposed for release in the U.S.A. Proposals for release of the pathogen will be developed for review by the Technical Advisory Group for Biological Control Agents of Weeds, and subsequent development of an Environmental Assessment, declaration of Finding of No Significant Impact and issuance of federal and state permits for release. Inoculum of the pathogen will be prepared in sufficient quantity for release, and target weeds will be inoculated in the field under conditions that favor disease development and establishment. Establishment and spread of pathogens will be monitored in the field by recording disease symptoms on the target weed and re-isolating the pathogens. Damage to target weed populations and environmental factors important in pathogen establishment, efficacy and spread, will be measured.
Under Objective 1, several endemic fungi have been isolated this year from infected target weeds for evaluation as potential biological control agents. Pathogenicity tests were conducted on Japanese hops (Humulus japonicas) using an endemic isolate of the fungal pathogen Colletotrichum firoinae. Multiple dew periods and various spray adjuvants were evaluated in order to optimize infection on Japanese hops. Two endemic fungal pathogens were isolated from diseased Japanese honeysuckle (Lonicera japonica) and are currently undergoing morphological and molecular characterization for identification. An Entomosporium sp. was isolated from diseased Xylosa sp. from Louisiana and is undergoing morphological and molecular characterization. A fungal pathogen isolated from diseased mile-a-minute (Persicaria perfoliata) last year was identified as a Phoma sp. based upon spore morphology. Inoculations of mile-a-minute plants with the Phoma sp. under controlled greenhouse conditions are ongoing. A Cercospora sp. was isolated from diseased Pennsylvania smartweed (Polygonum pensylvanicum L.) and identified using morphological characteristics. Inoculations of Pennsylvania smartweed plants with the Cercospora sp. under controlled greenhouse conditions are ongoing. Plants were inoculated with Uromyces salsolae, a candidate for biological control of Russian thistle (Salsola tragus) and histological samples were prepared in order to complete the characterization of the life cycle of the pathogen.