Location: Foreign Disease-Weed Science Research2021 Annual Report
Objective 1: Isolate, identify, and evaluate endemic plant pathogens that can be utilized as biological control agents of invasive weeds, such as swallow-wort, garlic mustard, and Japanese hop. [NP304, Component 1, Problem Statement 1C; Component 2, Problem Statement 2B] Sub-objective 1.A – Isolation and identification. Sub-objective 1.B – Evaluation of pathogen efficacy. Sub-objective 1.C – Evaluation of disease reaction among non-target and target species. Sub-objective 1.D – Develop and submit a proposal for release, and if approved, participate with cooperators in release and post-release monitoring of the pathogen(s). Objective 2: Determine the diversity and population dynamics of microbes associated with invasive weeds. [NP304, Component 1, Problem Statement 1C; Component 2, Problem Statements 2A and 2B] Sub-objective 2.A – Characterize the microbiome/virome of invasive weed species. Sub-objective 2.B – Evaluate the emergence of endemic phytopathogens on non-native, invasive weed species. Sub-objective 2.C – Develop accurate and rapid means for identification and detection of microbes permitted for field release. Objective 3: Develop innovative technologies to enhance or complement biological control agents and suppress weed health, such as RNA interference and encapsulation matrices. [NP304, Component 2, Problem Statement 2A] Sub-objective 3.A – Evaluate the efficacy and applicability of exogenous double-stranded RNA applications for plant health suppression. Sub-objective 3.B – Evaluate encapsulation matrices that support microbe survival and disease development.
Plant pathogens and plant-associated microorganisms will be collected from target invasive weeds in the U.S.A, and evaluated for their potential use as biological control agents using conventional, molecular, and technology driven approaches. The conventional approach is a cyclical method that identifies and evaluates promising candidate plant pathogens as biological control agents of invasive weeds. The molecular approach leverages advances in genomics to characterize and exploit weed microbiomes and viromes for insights into pathogen emergence and novel microbial candidates for host suppression. The technology driven approach will investigate technological advances to augment microbial-based biological control agents and to provide value-added synthetic properties to increase disease development under diverse environmental conditions. Microorganisms 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 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. Microorganisms determined to have an adequately narrow host range will be proposed for release in the U.S.A. Proposals for release of the microorganism 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 microorganism 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 microorganisms will be monitored in the field by recording disease symptoms on the target weed and re-isolating the microorganism. Damage to target weed populations and environmental factors important in microorganism establishment, efficacy and spread, will be measured.
Microbial biopesticides offer a cost-effective and sustainable approach for integrated weed management that helps mitigate the spread of invasive weeds in our natural and agricultural systems. Evaluating pathogens of invasive weeds is a multistep process that includes identification, evaluation, petitioning, release, and monitoring disease development following a field release. Under Objective 1A, multiple endemic plant pathogens were isolated and characterized from invasive weeds, including fig buttercup (Ficaria verna), orange daylily (Hemerocallis fulva), Russian knapweed (Rhaponticum repens), yellow star-thistle (Centaurea solstitialis), cleavers (Galium sp.), garlic mustard (Alliaria petiolata), and hoary cress (Lepidium draba). In addition to the newly identified putative pathogens, research is continuing on previously identified endemic pathogens from past collections that include, fungal and bacterial pathogens from black swallow-wort (Vincetoxicum nigrum), poison hemlock (Conium maculatum), English ivy (Hedera helix), periwinkle (Vinca minor), mile-a-minute (Persicaria perfoliata), Japanese hop (Humulus japonicus), and garlic mustard. Isolate characterization and whole plant inoculations are ongoing. Following the completion of Koch’s Postulates, promising endemic pathogens will undergo efficacy and host specificity analyses. Two promising fungal pathogens isolated from diseased Japanese hop are currently undergoing molecular characterization and efficacy studies. Under Objective 1B, the previously characterized endemic bacterial pathogen (Xanthomonas campestris) of garlic mustard is currently undergoing host range and efficacy trials. Under Objective 1D & 1E, the petition to release a fungal pathogen (Ramularia crupinae) to control the federally noxious weed common crupina (petition # 13-03) has been approved by the Animal and Plant Health Inspection Service and the Environmental Protection Agency for field trials. Collaborations have been developed with ARS, university, and state scientists from Idaho, Oregon, California, and Washington. Preliminary field trials are anticipated to begin in fiscal year 2022. Under Objective 2B & 2C, the genomes of X. campestris of garlic mustard and R. crupinae of common crupina were sequenced or currently in the process of being sequenced, respectively. Whole genome sequences will allow for the development of DNA-based diagnostic assays for monitoring pathogen establishment in the field and comparative genomic studies.
1. Regulatory approval of the fungal biological control agent for use against the federally noxious weed, common crupina. Rangelands and grasslands, comprising 30% of land cover in the U.S., are challenging environments in which to manage invasive weeds due to their geographical size, diverse topographies, cyclical stress events (e.g., droughts and wildfires), and diversity of plant species; thereby, costing land managers and growers $6 billion annually in damages and management costs. The federally noxious weed, common crupina (Crupina vulgaris), infests thousands of hectares of grasslands in Idaho, California, Washington, and Oregon, resulting in the degradation of native and beneficial plant communities and the reduction of rangeland forage productivity. Microbial-based biological control agents of non-native, invasive weeds can provide a cost effective and sustainable approach to weed management for these large, ecologically sensitive regions with diverse plants and terrain types since microbial agents can be host-specific, persistent, environmentally safe, and self-propagate. Following extensive greenhouse studies and regulatory reviews, the host-specific fungal pathogen, Ramularia crupinae, has received the necessary permits and approvals required to begin limited field releases in the Western United States to help manage this noxious, invasive weed. Decreasing common crupina populations will directly benefit U.S. agriculture by increasing rangeland forage productivity and livestock carrying capacity, preserving native and beneficial plant communities, preventing the displacement of rare and threatened species, and reducing the funds and resources necessary to maintain long-term common crupina management operations.