Location: Foreign Disease-weed Science Research2012 Annual Report
1a. Objectives (from AD-416):
1. Discover, identify and evaluate the efficacy of exotic pathogens as classical biological control agents of invasive weeds such as Canada thistle, Russian thistle, Russian knapweed, yellow starthistle, and medusahead. 1A - Discovery 1B - Isolation and identification 1C - Evaluation of pathogen efficacy 2. Conduct risk analyses to determine the agricultural and ecological safety for the release of pathogens as classical biological control agents, such as Colletotrichum gloeosporioides f. sp. salsolae and Phoma exigua. 2A - Development of test plant lists 2B - Evaluation of disease reaction among non-target and target species 3. Develop an improved process of risk assessment using plant pathogens as a model system. 3A - Integrate DNA sequences of species on the basic test plant list into host- range evaluation with Mixed Model Equations 3B - Generate BLUPs of species on the basic test plant list 3C - Determine true host range of each pathogen by including DNA sequences and disease reaction data of other closely related species. 4. Release and, with collaborators, monitor and evaluate impact of pathogens on weed populations and non-target effects in the field. 4A - Develop and submit a proposal for release that describes the importance of the target weed as a pest and the efficacy and safety of the candidate pathogen. 4B - Participate in the regulatory decision process as needed. 4C - Participate with cooperators in release (with permit from state and federal regulators) and post-release monitoring of the pathogen).
1b. Approach (from AD-416):
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, yellow starthistle, and medusahead. Other targets include, but are not limited to: Carduus thistles, milk thistle, knapweeds, common crupina, whitetop, broadleaved pepperweed, Himalaya 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, an improved method of risk assessment will be developed and used. This improved method 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. 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.
3. Progress Report:
Several new diseases of invasive weeds in the U.S. were discovered in 2012. In both Kyrgyzstan and Russia, dying Ailanthus altissima trees were found and diseased tissue is being sent to our laboratory for pathogen isolation and testing. An epidemic of leaf necrosis was also found on Cirsium arvense in Kyrgyzstan. In Turkey, both rust and leaf spot diseases were found on Chondrilla juncea, and an epiphytotic of leaf yellowing was found on Lepidium latifolium in Russia. Diseased specimens from an Ambrosia sp. were also collected. A pathogen, Colletotrichum gloeosporioides, was isolated from Persicaria perfoliata previously collected in Turkey, and proofs of pathogenicity were completed. This weed (mile-a-minute) is a serious invasive weed problem on the east coast of the U.S. Another pathogen, Colletotrichum lineola from swallow-wort, in Russia, is being evaluated as a potential biological control agent for two species of swallow-wort in the U.S. Nine pathogens of field bindweed (Convolvulus arvensis) were evaluated for effectiveness in controlling this weed. The rust fungus Puccinia punctiformis was evaluated in field tests, in Maryland, Greece, and Russia, for its potential to control Canada thistle. In all locations, epiphytotics of the rust were successfully initiated and can be routinely established on Canada thistle, which should lead to implementation of successful biological control with the rust. A new disease caused by Pilidium concavum was identified on Japanese knotweed (Fallopia japonica) from Oregon, and distribution of the disease in the U.S. is being determined. Koch’s postulates are in progress for two fungi from Brazilian peppertree (Schinus terebinthefolius). Tests of Armenian blackberry rust, caused by Phragmidium violaceum, reveal a differential response among U.S. blackberry accessions, indicating that Armenian blackberry is a complex of Rubus species that differ in susceptibility. (The foregoing research relates to objective 1 of the project) The rust pathogen, Uromyces salsolae from Russian thistle has been approved by the Technical Advisory Group of APHIS and final review and consultation with our laboratory is being conducted by APHIS for release in the U.S. A petition for release of C. gloeosporioides on Russian thistle is planned pending a name change of the pathogen to C. salsolae. Petitions for release of two facultative pathogenic fungi, Boeremia exigua and Ramularia crupinae, which cause significant damage on Russian knapweed and common crupina, respectively, are nearly ready for review by the TAG. (The foregoing research relates to objective 4 of the project) As part of the host range determination process, a new approach integrating DNA sequences and disease reaction data into mixed model equations was validated by comparing predictors from the model with original disease reaction and post-release data for two released biological control pathogens. (This research relates to objective 3 of the project) The host range determination process has been completed for Ramularia crupinae on common crupina. Only common crupina is susceptible to the fungus. (This research relates to objective 2 of the project)
1. Improved methodology for host range determination. The host-ranges of two biological weed control pathogens previously released in the USA were re-evaluated with the mixed model equations (MME) by incorporating DNA sequences of the plant species and historical host-range data to generate Best Linear Unbiased Predictors (BLUPs) of disease reaction. Results showed that: BLUPs confirmed the narrow host range of the two pathogens; BLUPs supported and substantiated currently available information on host range; BLUPs were accurate predictors of host range, particularly concerning susceptibility of any non-target species in the field; and no new, unforeseen non-target effects could be expected in nature on the basis of BLUPs. This approach was validated by ARS researchers at Frederick, Maryland for MME analysis by predicting known field host-range of biological control pathogens from greenhouse data.
2. Control of Canada thistle rust. Canada thistle rust (Puccinia punctiformis) is either native or naturalized in all areas of the world where the weed occurs. Despite being studied for over 100 years the disease cycle had not been completely understood and this had prevented epidemics of the rust from being successfully initiated and used for biological control. Research results found by ARS researchers at Frederick, MD indicate that inoculation of Canada thistle rosettes with teliospores or teliospore-bearing leaves, in September, (in the northern hemisphere) consistently leads to establishment of systemically diseased shoots the following spring and epidemics of the rust in subsequent seasons. This has now been accomplished in Maryland, Greece, and Russia. These successes indicate that epidemics of the rust fungus can be routinely initiated and have the potential to control Canada thistle.Berner, D.K., Bruckart, W.L. 2012. Comparing predictions from mixed model equations with host range determinations from historical disease evaluation data of two previously released weed biological control pathogens. Biological Control. 60:207-215.