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Research Project: DISCOVERY AND CHARACTERIZATION OF PLANT PATHOGENS FOR BIOLOGICAL CONTROL OF INVASIVE WEEDS FROM THEIR NATIVE RANGE

Location: Foreign Disease-Weed Science Research

2014 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:
Forty three pathogens, from diseases of Ailanthus altissima, Anchusa officinalis, Cirsium arvense, Cytisus scoparius, Hedera helix, Microstegium vimineum, Rubus armeniacus, Rubus phoenicolasius, Rubus spp., and Schinus terebinthifolius were either isolated or acquired in 2014. Proofs of pathogenicity were completed for three pathogens, identified to species, and seven other pathogens were identified to genus. Proof of pathogenicity was also fulfilled with Septoria lepidii from Lepidium draba, a very promising pathogen of a particularly difficult target weed related to many cultivated Brassicaceae species. Epiphytotics of systemic disease on Canada thistle (CT) caused by the rust fungus Puccinia punctiformis were successfully initiated in Greece, New Zealand, Russia, and the USA, demonstrating that epiphytotics of systemic disease can be routinely established on CT. Thistle density data from 2009 through 2014 in these locations in Greece, Russia, and the USA have been analyzed. The non-linear regression of exponential decline was thistle shoots per square m =27.10 x exp (-.0595 x months after inoculation). Based on this regression, thistle density is predicted to decline to 1 shoot per square meter at about 42 months after inoculation. The Colorado Dept. of Agriculture, through a specific cooperative agreement, inoculated 11 sites with the rust in 2013 and is targeting 100 sites in 2014. A new disease caused by Bipolaris microstegii was identified on Japanese stiltgrass (JSG) from Maryland. Koch’s postulates were satisfied and comparison of 12 isolates of Bipolaris vs. four accessions of JSG, suggest a complex of two Bipolaris species and possibly two JSG types. Tests of Armenian blackberry rust, caused by Phragmidium violaceum, suggest a differential response among accessions from the U.S. supporting the conclusion that invasive blackberry in the U.S. is really a complex of Rubus species (Objective 1). A petition for release of Colletotrichum salsolae on Russian thistle was submitted to TAG (petition # 14-001). Petitions for release of two facultative pathogenic fungi, Boeremia exigua and Ramularia crupinae, which cause significant damage on Russian knapweed (RK) and common crupina, respectively, are under review by the TAG (Objective 4). As part of the host range determination process, ITS sequences of target (Crupina vulgaris) and non-target weeds were obtained from GenBank and generated at FDWSRU. Genetic distance matrices and phylograms among target and non-target plants were constructed on the basis of these sequences, and BLUPs of species were generated after integrating disease reaction data and genetic distance matrices into Mixed Model Equations (Objective 3). The host range determination process has been completed for Boeremia exigua var. rhapontica on RK and Ramularia crupinae on common crupina. Only the target weeds were found susceptible to the pathogens (Objective 2). Establishment of Puccinia jaceae at the release site in Oregon was documented for the first time this year.


4. Accomplishments


Review Publications
Bruckart, W.L., Eskandari, F., Berner, D.K. 2014. Characterization and evaluation of target and host: Ramularia crupinae, a candidate for biological control of two varieties of Crupina vulgaris in the United States. Mycoscience. 71:40-48.
Berner, D.K., Smallwood, E.L., Cavin, C.A., Lagopodi, A., Kashefi, J., Kolomiets, T., Pankratova, L., Mukhina, Z., Cripps, M., Bourdot, G. 2013. Successful establishment of epiphytotics of Puccinia punctiformis for biological control of Cirsium arvense. Biological Control. 67:350-360.
Bruckart, W.L., Eskandari, F., Lane, W. 2014. First Report of Leaf Necrosis on Microstegium vimineum caused by Bipolaris microstegii in Maryland. Plant Disease. doi:org/10.1094/PDIS-11-13-1122PDN.
Tunali, B., Cavin, C.A., Berner, D.K. 2014. First report of leaf spot of Convolvulus arvensis caused by Phoma macrostoma var. macrostoma in Turkey. Journal of Plant Pathology. 96:434.
Berner, D.K., Lagopodi, A., Kashefi, J., Mukhina, Z., Kolmiets, T., Pankratova, L., Kassanelly, D., Cavin, C.A., Smallwood, E.L. 2014. Field assessment, in Greece and Russia, of the facultative saprophytic fungus, Colletotrichum salsolae, for biological control of Russian thistle (Salsola tragus). Biological Control. 76:114-123.