W1193: Locoweed and its Fungal Endophyte: Impact, Ecology, and Management
(Multistate Research Project)
W1193: Locoweed and its Fungal Endophyte: Impact, Ecology, and Management
Duration: 10/01/2015 to 09/30/2020
Statement of Issues and Justification
Locoweeds are the most widespread group of poisonous plants in the western United States (Allred, 1991; Graham et al., 2009). Consumption of toxic species within the plant genera of Astragalus and Oxytropis, within the Fabaceae, cause locoism to grazing animals (Knight and Walter, 2003). Locoism is caused by consumption of the indolizidine alkaloid swainsonine (SWA), an alpha-mannosidase inhibitor (Dorling et al., 1980). Locoism symptoms include reproductive problems, cellular vacuolization, neurological damage, and lack of coordination (James, 1970; James et al., 1981; James et al., 1992). Livestock poisoning from locoweeds causes major economic losses in several western states. While the magnitude of economic loss depends on the degree of intoxication, losses from locoweeds due to poor animal health, low reproductive performance, increased death and reduced weight can cause reductions in cattle prices from 10% to 85%. In New Mexico in 1985, over 10% of the cow/calf and 40% of the cow stocker operations reported losses of over $20 million from locoism (Torell et al., 2000).
Most plants in natural ecosystems are hypothesized to interact in symbioses with fungal endophytes (Rodriguez et al., 2009), often in mutualism because the fungal endophyte gains a home, a source of nitrogen and carbon resourses, while providing a variety of benefits to the plant host. Fungal endophytes of locoweeds (genus Undifilum) produce the alkaloid swainsonine and are thus responsible for the locoism disease symptoms (Braun et al., 2003; Pryor et al., 2009). The endophytes are seed transmitted and generally do not cause disease to their plant host (Oldrup et al., 2010). Similarly, fungal endophytes of grasses produce alkaloids toxic to grazing mammals. Research on the grass-fungal endophyte system has shown host benefits including herbivore defense (Clay 1990), increased heat and drought tolerance (Bacon and White., 2000), and improved plant vigor and resistance to some pathogens (Molyneux et al., 2007). In contrast, the benefits provided by the fungal endophytes to locoweed plants are not known. As a consequence, the ecological relationship between the endophytes and locoweeds has not been well-defined. However, plants grown without the endophytes are non-toxic high quality forage. A better understanding of the endophytic fungi, including how they produce swainsonine and how they interact with their plant hosts, will contribute toward long term management solutions with understanding of the toxic compound quantity and accumulation in hosts and locoweed population establishment and occurrence, respectively.
Locoism causes severe life and economic losses to domestic and wild ungulates. Locoism is caused by the consumption of the toxic alkaloid SWA which is produced by a fungal endophyte associated with locoweeds of the Astragalus and Oxytropis genus. However, the biosynthetic pathway for swainsonine production remains unknown. A better understanding of factors that affect SWA levels within the host plant as well as between populations on range lands needs to consider both the locoweed host plant and its fungal endophyte. This is because although the fungal endophyte produces SWA, it most likely receives its nutrients from its host plant to do so (Delaney et al., 2011; Vallotton et al., 2012). Also, the success of the fungal endophyte, and its distribution, depends on the success of the locoweed host since the fungus is only vertically transmitted through seed coats. Finally, although vertebrate herbivores may not be deterred by SWA when preferred food plants are unavailable, 20% of cattle tested were willing to consume new plants like locoweed and social interactions among cattle can promote many individuals to consume locoweeds in a relatively short time (Graham et al, 2009). With the small yet pervasive populations of many species of locoweed throughout many western rangelands, providing non-toxic forage for grazing can only be accomplished by a thorough understanding of the interaction between host plants and their corresponding endophytes.
Effective management of locoweeds and locoism has been difficult to implement and costly despite the prevalance of locoism in the United States for over a century (Marsh, 1909). Recommendations include restricting access to pastures for grazing in the spring, supplementing cattle feed so that they don’t graze on locoweeds, spraying herbicides during locoweed flowering, and using insects for biocontrol (Graham et al., 2009). Behavior modification of cattle and horses shows promise as a management option, although large scale feasibility has not been determined. A valuable, sustainable management program that can be implemented in multiple states is needed for this difficult problem.
Understanding locoweed-fungal endophyte interactions can significantly impact several research areas: plant/microbe interactions, microbe-induced plant defense against herbivores, rangeland management, secondary metabolite production (plant or fungal production control), plant resource investment into an asymptomatic endophyte, plant abiotic and biotic stress tolerance, plant biogeography, and the continuum between mutualistic and commensalistic interactions where locoweed/endophyte system seems to fall. Locoweed-fungal endophyte interactions are also of interest by being quite different from the tall fescue-fungal endophyte complex where the fungus produces a toxic alkaloid, but also enhances plant growth.
We propose establishment of a regional project to study locoweeds and their fungal endophytes to monitor locoism impacts on the rangeland grazing communities and collaborate for management solutions. Locoweeds and locoism cause problems over a large area and the researchers that are experts in the field that address the problem are spread over several states and over different agencies, ie. ARS and USDA. A multistate project will improve communication and research efficiency. This group will meet annually to discuss, assess, and prioritize research topics such as locoweed genetics, endophyte genetics, plant and fungal ecology and physiology, and locoism detection and management. The group will develop an action plan to determine who will accomplish which aspects of the research, including identifying research of high impact for locoism management, and who will work together to seek funding for the highest priority research. The group will coordinate research to provide preliminary information needed to secure grant funding. The group will also bring together research resources including plant and fungal samples collected from various locations and seed of various locoweed species, and provide periodic written documents reviewing the status of locoweeds, endophytes, and management both for dissemination among collaborating institutions and throughout range communities.
This research will lead to a better understanding of the interaction of plant and endophyte on swainsonine concentrations and subsequent effects on grazing animals. Through increased understanding of this tripartite interaction of fungus-plant-animal, we may be able to develop strategies to eliminate swainsonine or change the dynamics of the endophyte in naturally occurring populations of locoweed. Incorporating research from multiple states will contribute to management solutions for local, state-wide, and national locoism problems as well as decreasing duplication of research and increasing dissemination of results. This work can benefit society by helping to more completely understand locoweeds and how a toxic alkaloid is produced by a fungus, which in turn may ultimately protect the food supply by aiding ranchers whose livestock suffer from locoism.
Related, Current and Previous Work
There are no current ongoing regional projects to address locoweeds and their endophytes. There has been a project SERA008 Fescue Endophyte Research and Extension that addresses research on a different fungal endophyte system that causes toxicoses for grazing animals. That project involves a different type of plant (fescue grass) and an unrelated grouping of fungal endophytes. We hope to build on the similarities between the systems and some of the accumulated expertise to help us with our project.
Assemble a group which will include university, government, extension, and industry-based individuals to assess the current status of locoweeds, locoism, and fungal endophytes of locoweeds and set priorities for research.
Identify of locoweeds and endophytes in the western US.
Determine the biochemistry of swainsonine biosynthesis and metabolism.
Determine the ecology and physiology of locoweed plants in the western US.
Develop management tools for locoweeds.
Objective 6. Develop tools and coordinate management of locoism;
MethodsObj 1: Assemble a group which will include university, government, extension, and industry-based individuals to assess the current status of locoweeds, locoism, and fungal endophytes of locoweeds and set priorities for research. Individuals working on different aspects of locoweeds, their endophytes, and management have begun working together. Those committed to joining the group include university mycologists and molecular biologists, university and government plant physiologists, university and government range scientists, and an entomologist from New Mexico, Montana, and Utah. The committee will meet annually to discuss the status of locoism, locoweeds, and their fungal endophytes in the western US and present the latest developments in research. At the annual meetings, the group will also discuss gaps in the knowledge related to locoweeds and set priorities for research. The annual meeting will provide a forum for distribution of current and ongoing research that may not yet be available by other means which in turn will allow for discussion, exchange of ideas, and identification of issues at the forefront of the locoism problem. The objectives presented below were named as likely research topics by potential committee members. Obj 2: Identify locoweeds and endophytes in the western US. (New Mexico, Montana, Utah) It is important to conclusively identify which plants and populations are actually toxic and determine the levels of toxicity. New Mexico and Utah (USDA ARS) are pursuing a collaborative project to determine which Astragalus and Oxytropis species throughout the western US contain a fungal endophyte and thus swainsonine. There are many unsubstantiated reports of toxic locoweeds and in many cases, the type of toxicity was never documented. Previous research has identified three species of Undifilum associated with varying species of locoweeds. From new plant species and populations that are found to contain swainsonine, we will isolate and characterize the associated endophytes. Endophytes will be characterized both as species and also compared using phylogenetics with species worldwide. New Mexico, Utah (USDA ARS) and Kentucky have begun a collaborative project to determine the nucleic acid sequence of several species of locoweed endophyte. We anticipate sequencing the genome of two additional swainsonine-producing fungal taxa. Obtaining complete sequence is essential to understand the relationships between the different endophytes, the relationship between endophytes and their hosts, and to determine the endophyte enzymes associated with secondary metabolite production and symbiosis. Obj 3: Determine the biochemistry of swainsonine biosynthesis and metabolism. (New Mexico, Utah, Kentucky) Understanding the components of the swainsonine biosynthetic pathway is crucial for development of any comprehensive management plan for locoism. This includes identification of the enzymes and intermediates within the pathway for different endophyte species and how those enzymes are regulated. New Mexico, Utah (USDA ARS) and Kentucky have begun to characterize the swainsonine biosynthetic pathway based on the endophyte sequence obtained through genetic manipulation and proteomic studies of toxic vs non-toxic related fungal species. This collaboration has initiated experiments to knock out key pathway enzymes to verify their role in swainsonine production. Further research using the sequence data obtained during endophyte identification can also enhance understanding of enzymatic regulation and control for swainsinone production. Establishing the complete biosynthetic pathway will enable further research on plant-fungal symbiotic interactions and potential for toxin degradation options within plant and possibly grazing mammals. Obj 4: Determine the ecology and physiology of locoweed plants in the western US. (Montana, Utah) Populations of locoweeds occur in several different conditions throughout the western US. Additionally, the two genera of locoweeds, Astragalus and Oxytropis contain many different species. Because of this, generalizations cannot be made for the plant and its endophyte and comprehensive studies are needed for complete understanding of ecological roles of the plant and physiological states of endophyte and host under differing conditions. New Mexico found that the endophyte can limit locoweed growth under certain conditions, and subsequent studies are needed to clarify putative endophyte effects on the competitiveness of locoweed plants. Specifically, additional experiments are needed to determine the influence of endophytes on resource allocation in competing plants, as well as experiments to determine the effects of endophytes on the competitiveness of locoweed plants grown under resource-limited conditions. Improved knowledge of endophyte effects on the competitiveness of locoweed plants will contribute to a comprehensive framework for understanding the ecological implications of the locoweed-endophyte relationship that is unique from other plant-endophyte interactions (e.g., grass-endophyte symbiosis). Also, studies that clarify endophyte effects on the competitiveness of locoweed plants may improve our ability to predict the occurrence and spread of locoweed populations under various ecological conditions. Utah (USDA ARS) is interested in determining how climate change (elevated CO2) will effect plant biomass and swainsonine concentrations. A collaboration between Utah and New Mexico is interested in characterizing the fungal and bacterial microbiomes in endophyte-infected and non-infected plants and evaluating the relative fitness of endophyte-infected and non-infected plants. Montana is interested in determining the role of endophytes on plant defense. They found in preliminary work that antimicrobial compounds are decreased in endophyte-containing plants, suggesting that the fungus may be regulating the plant’s defense mechanism to allow for infection. The extent of the regulation and the impact of that regulation will be studied. The group determined that endophyte-containing plants had lower levels of volatile compounds associated with antimicrobial activity and defensive metabolites after wounding. The group will explore differential gene expression in host plants to determine the mechanisms involved in endophyte fitness. Obj 5: Develop management tools for locoweeds. (New Mexico, Utah) Current management options for ranchers are exceptionally insufficient considering the extent of locoism problems. New Mexico plans to continue fine tuning targeted grazing prescriptions aimed at suppressing white locoweed population outbreaks. Initial studies showed the feasibility of using sheep to promote local short term suppression of white locoweed infested patches. This research also showed that intermittent grazing is able to achieve locoweed control objectives without compromising animal health. Targeted grazing appears to be most effective when used in an integrated program as a means of extending the life of proven weed control methods such as herbicides. Future research on management of locoweeds will include developing integrated approaches to suppress population outbreaks. Utah is interested in testing fungicide treatment of plants to reduce swainsonine concentration. Maintaining a population of population of locoweed that could be made non-toxic would increase forage options for ranchers. Fungicide treatments of plants has been effective at reducing or eliminating the endophyte in the greenhouse. The feasibility of fungicide treatment on a larger scale will be assessed. Obj 6: Develop tools and coorcinate managament of locoism. (Utah, New Mexico) Collaborating and coordinating research will streamline both develop of management tools and identification of areas of high need for management. The multi-state approach will allow for review of management tools effective at both local and regional levels. A new assessment of losses suffered by the livestock industry in the western United States is also of high necessity to provide context and direction to ongoing locoweed research efforts. We anticipate collaborations with Agricultural Economists to conduct new county-level assessments of the economic impacts of locoism.
Measurement of Progress and Results
- The primary product of this project will be data and information, as well as management recommendations. The types of expected data include nucleic acid sequence from locoweeds and endophytes, new species descriptions for novel fungal endophytes, phylogenetic trees, protein structure information, toxin biosynthtetic pathways, data on ecological interaction parameters, data on efficacy of management strategies, and management recommendations. A joint publication reviewing the group accomplishments is the anticipated output at the end of the 5 year cycle.
Outcomes or Projected Impacts
- The primary outcome for the project is increased comprehension of how the endophytes produce swainsonine, how they interact with their hosts, and how locoweeds and locoism can be managed.
- Results will lead to a more comprehensive understanding of the interaction of plant and endophyte on swainsonine concentrations as well as contribute to the knowledge of ecologically significant plant-fungal symbioses.
- This information will support progress in managing locoism with the potential to develop strategies to eliminate swainsonine or change the dynamics of the endophyte in naturally occurring populations of locoweed.
- Overall, this work can benefit society by helping to understand locoweeds and how a toxic alkaloid is produced by a fungus, which in turn may ultimately protect the food supply by aiding ranchers whose livestock suffer from locoism.
Milestones(2016): While most of the projected research is not dependent on any prior research, culturing endophytes and obtaining sequence for their genetic fingerprinting must be accomplished prior to characterizing the new endophytes.
(2017): A complete genomic sequence of at least two endophytes will need to be accomplished before the biosynthetic pathway can be confirmed and type of symbiosis between plant and fungus can be characterized.
(2017): Research on ecological and physiological roles of locoweed plants, their endophytes, and complete populations will occur concurrent with research on the biosynthesis of SWA. Assessing populations and plant fitness, with and without associated microbial organisms can be accomplished across several states in parallel.
(2018): Combining milestones of 1) elucidating biosynthetic pathway of SWA and 2) examining ecological roles of locoweed populations and plant-fungus interactions with grazing animals will be primary determining factors for identifying management strategies.
(2019): Strategies will be investigated for efficacy and application feasibility at local and regional levels.
Projected ParticipationView Appendix E: Participation
The results of the project will be disseminated through refereed publications, extension bulletins, field days, and a jointly produced review publication. Some participants (Loest, Cibils, Panter) already have developed stakeholder communication pathways with ranchers and cattlemen in their states (New Mexico and Utah) and further pathways for direct communication with ranchers in other states will be established. Current knowledge of locoism problems is inconsistent among public, especially concerning facts that the fungus only (not the plant as previously thought) produces the toxin. Additionally, there could be non-research based management practices used by ranchers that have not been communicated outside of local groups. Combining team members from several different states and establishing a route of communication directly to ranchers will help bridge these gaps in knowledge.
The group will be governed by an executive committee composed of 1-2 representatives from each of the participating institutions. The representatives will be selected by the individuals at each institution. The executive committee will help plan and organize annual meetings, produce annual reports, and establish subcommittees for specific tasks such as the review publication.
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