The overall objective of this project is to develop and utilize some bioherbicide agents that have been previously demonstrated to be effective in preliminary field trials. The project has four main objectives.
Objective 1: To evaluate and develop bioherbicide agents to control nutsedges, pigweeds, grasses, purslanes, spurges, kudzu, weeds in Asteraceae, and others.
Objective 2: To develop and evaluate formulations to improve performance and standardization of selected bioherbicides.
Objective 3: To evaluate bioherbicides in multistate field trials in different crops and as alternatives to methyl bromide.
Objective 4: To safely enhance the virulence of bioherbicides by selection of variants of the plant pathogen that overproduce a target amino acid.
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In 1995, the S-268 Regional Research Project was initiated to evaluate and develop plant pathogens for biological control of weeds. S-268 succeeded two previous projects, S-136 and S-234, and collectively these cooperative projects served as the foundation for research and evaluation of nearly two dozens of pathogens as potential bioherbicides. These projects also helped to develop epidemiological and risk-analysis models to understand the performance and safety of two previously registered and commercialized bioherbicidal pathogens, Colletotrichum gloeosporioides f. sp. aeschynomene (Collego®), used for the control of northern jointvetch (Aeschynomene virginica), and Phytophthora palmivora (DeVine®) used for the control of stranglervine (Morrenia odorata) in Florida, understand some aspects of the genetics of these fungi, and develop systems to integrate their use in rice and citrus production. It also provided a forum to develop scientific and technical concepts helpful in the registration but not commercialization of Puccinia canaliculata as Dr. BioSedge®.
Several other bioherbicide candidates were developed through regional trials, notably Alternaria cassiae, although registration and commercialization of this agent did not materialize. While in some cases this was simply due to a lack of consistency of the bioherbicide agent or technical feasibility, the availability of efficacious chemical alternatives, coupled with the lack of coordinated efforts by researchers and commercial enterprises were also contributory factors. Nonetheless, it has been amply demonstrated that bioherbicide products are practical and economically sustainable in specialty markets. Moreover, their use over the past 25 years has not led to any risks to human health or the environment. The basic and applied research done through these cooperative projects have helped to develop and validate the concept of inundative biological control of weeds by the bioherbicide strategy.
The success of the S-268 project and its predecessors can be measured also in terms of the scientific and technical knowledge gained. The members of this group have written two books, hundreds of refereed papers, reviews, book chapters, and popular articles on the subject of biological control of weeds with plant pathogens. About twenty-five graduate students have been trained since the inception of the first cooperative project on this topic, S-136. Three bioherbicides have been registered and a classical biocontrol introduction of a rust fungus has resulted during this period. Several prospective bioherbicides have been patented.
Just during the last five years, under S-268, three pathogens have been cooperatively developed: Colletotrichum truncatum (COLTRU) for control of hemp sesbania (Sesbania exaltata), Alternaria destruens (Smolder) for dodders (Cuscuta spp.), and Pseudomonas syringae pv. tagetis for control of several weeds in the Asteraceae. Smolder is currently under EPA review for registration. In addition, these regional projects have also helped to stimulate research on the use of novel materials for formulation, or as surfactants and spray adjuvants to improve the efficacy and host range of bioherbicide agents, improve production methods, and develop effective delivery systems. During this period, 97 refereed papers, 19 book chapters, 33 papers in conference proceedings, 51 abstracts, and 9 patents, and several miscellaneous publications were produced by the members and other participants of S-268 project. These contributions would not have been possible without the facility to engage in cooperative regional research under the auspices of S-268. In addition, the project has enabled the discovery of numerous new pathogens or pathogen records on weeds and clarification of weed and pathogen taxonomies, understanding of the epidemiology of several diseases, development of methods for microbial fermentation, formulation, and delivery, risk assessment, and molecular biology of host-pathogen relationships.
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The first weed-control pathogens were discovered and deployed between 1969 and 1973 (Daniel et al., 1973; Smith, et al., 1973 a, b; TeBeest and Templeton, 1985; Ridings, 1986; Templeton et al., 1986). By 1982, 49 plant species were reported as targets for control by bacteria, fungi, nematodes, and viruses (Templeton, 1982). Recent analyses indicate that nearly 200 fungal pathogens have been screened as potential bioherbicides (Charudattan 1991, 2001). Of these, eight pathogens have been registered worldwide and about 50 are rated as having good to excellent potential for commercialization. About 46 different weeds have been identified as potential targets for bioherbicide research in different countries. About a third of these weeds are also the primary targets in the United States.
Several ongoing regional research projects address various aspects of biological control, including some in the Southern Region. However, only one other project, S-303, deals with biological control of weeds and complements this proposed multistate project on the development of plant pathogens as bioherbicides. The two projects are different in that the S-303 project deals with biocontrol of introduced insect pests and weeds through classical importation of biocontrol agents, while the proposed project is aimed at the use of indigenous plant pathogens in augmentative and inundative biocontrol strategies.
Only one other multistate project related to weed biocontrol is in existence. This project, S-303, deals with classical biological control of arthropod pests and weeds through importation of natural enemies from abroad. This project has four objectives, including survey and importation of natural enemies of invasive pests; integration of exotic and indigenous natural enemies with other pest management approaches; evaluation of the effects of exotic natural enemies on nontarget organisms; and characterization of the role of indigenous natural enemies in suppressing pest and beneficial species. These objectives and the general aim and scope of this project do not conflict or duplicate the objectives proposed herein. The bioherbicide project proposed here deals exclusively with indigenous microbial plant pathogens used in the inundative biocontrol strategy. Accordingly, the proposed multistate project can compliment the S-303 project.
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Weed control is required to sustain and maximize agricultural productivity. Crop losses due to weeds in the United States are estimated to be nearly $6 billion per annum, and losses due to weeds in major crops in the United States, such as wheat, maize, rice, and soybean are estimated at 11% to 21% of the attainable yields. In the Southern Region, losses due to weeds are said to exceed $1.7 billion. In the absence of weed control, it is estimated that crop losses in the United States would amount to $19.6 billion. These figures do not include the loss of productivity encountered in livestock production due to invasive weeds, the costs of weed control in natural areas (e.g., waterways and rangelands), recreational areas (e.g., golf courses and parkland), or urban and home landscapes.
Chemical herbicides and cultivation are used as the primary means of weed control in the United States. Based on pesticide sales figures, more herbicides are used than any other type of pesticide. Worldwide, chemical herbicides account for approximately 44% of the chemical pesticides used, compared with 29%, 21%, and 6% for insecticides, fungicides, and other pesticides (i.e., nematicides, plant growth regulators, etc.), respectively. The pesticide production figures in the United States also generally support these figures since the proportion of the acreage treated with herbicides or insecticides in 1988 were, respectively, 96% and 40% for corn, 95% and 4% for soybean, and 94% and 63% for cotton. Cessation of all pesticide use in the United States would reduce agricultural output, put farmers at an economic disadvantage, increase the cost of food, and may lead to food shortages.
Although chemical pesticides are an integral part of modern food production, there has been a significant cost to the society and the environment associated with the widespread use of these chemicals. Thousands of cases of accidental poisonings and numerous accidental deaths from chemical pesticides, including some herbicides, are reported each year. Extensive use of herbicides and other pesticides has resulted in groundwater contamination, and the use of certain herbicides has been linked to some types of cancer. Other preventable problems, mainly from misuse of chemical herbicides can result, such as nontarget damage from spray drift and carry-over problems in soil and produce.
Despite the extensive use of herbicides, many weed species continue to cause losses in agriculture, and the current strategies for control of these weeds are inadequate. One reason for this is the emergence of herbicide-resistant weeds. Many present-day herbicides have single-site modes of action and therefore are prone to promote rapid development of resistance among weeds. It took approximately 25 years for the first atrazine resistant weeds to be identified, but weeds resistant to sulfonylurea and imidazolinone appeared in less than 10 years after these herbicide chemistries were introduced and widely used. The intensive cultivation of herbicide-tolerant crops is likely to further accelerate the emergence of herbicide-resistant weeds consisting of mutant weed biotypes as well as naturally resistant weeds, the latter due to weed-shifting.
A different problem exists in some situations, such as vegetable crops (i.e., minor crops) and range lands, where the economic realities of the marketplace preclude the development and/or use of conventional chemical herbicides. Organic farming is gaining a foothold in the mainstream American agriculture, but this industry suffers from the general lack of biologically based weed control options. Foods consumed by infants, children, and elderly and commodities that rely on a few classes of herbicide chemistries for weed control are particularly vulnerable in this regard. Problems related to the current restrictions in the use of certain chemical herbicides and the impending loss of methyl bromide as a broad-spectrum soil fumigant will further exacerbate weed problems in crops such as vegetables, strawberry, and many others. Development of herbicide-tolerant crops, along with the consolidation of major agrochemical companies and increasing globalization of agricultural production and marketing further limit the choices available to manage weeds on local and regional scales. Many of these developments disproportionately constrain small and mid-sized farmers, especially given the recent depressed prices for commodities.
Invasive weeds are emerging as another major threat to agricultural and natural areas and to the long-term health and biodiversity of our nation’s land and water resources. Weed problems become more complicated in natural and urban areas, where economic, environmental, or human-health risks may entirely preclude the use of chemical herbicides. Lastly, weeds such as pigweeds (Amaranthus spp.), nutsedges (yellow nutsedge [Cyperus esculentus] and purple nutsedge [C. rotundus]), purslanes (Portulaca spp.), spurges (Euphorbia spp.), kudzu (Pueraria lobata), and various grasses and invasive weeds are not controlled effectively by available methods. Therefore, development of newer weed-management agents and technologies, including biologically based approaches, is of greater importance now than ever before.
One of the alternatives to chemical weed control is biological control by using plant pathogens. "Biological control" is defined as "management of natural enemies (predators, parasites, and pathogens of pests) and selected beneficial organisms (antagonists, competitors, and allelopaths) and their products to reduce pest populations and their effects". Plant pathogens used in an augmentative or inundative, biopesticide mode are referred to herein as bioherbicides.
Several other bioherbicide candidates were developed through regional trials, notably Alternaria cassiae, although registration and commercialization of this fungus did not materialize. While in some cases this was simply be due to a lack of consistency of the bioherbicide agent or technical feasibility, the availability of efficacious chemical alternatives, coupled with the lack of coordinated efforts by researchers and commercial enterprises were also contributory factors. Nonetheless, it has been amply demonstrated that bioherbicide products are practical and economically sustainable in the marketplace. Moreover, their use over the past 25 years has not led to any risks to human health or the environment. The basic and applied research done through these cooperative projects have helped to develop and validate the concept of inundative biological control of weeds by the bioherbicide strategy.
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Organization and Governance
The organization and conduct of this project will be in accordance with the rules and procedures set forth in the "Format for Multistate Research Proposals,” September 26, 2000 (http://msstate.edu/org/saaesd). This project will use the standard form of governance. A technical committee composed of one voting member from each SAES, one voting member from each USDA-ARS site, and as many participating members as approved from each SAES, USDA-ARS, and other institutional units. The Technical Committee will be responsible for planning the research project, coordinating the research activities of the participants, developing appropriate research methods and procedures for cooperative field trials, reporting of results, and for reviewing of research progress through annual meetings. The Executive Committee will consist of a Project Chair, a Secretary, 3 Objective Chairs, an Annual Meeting Chair, and the Administrative Advisor. The Project Chair, the Secretary, and the Objective Chairs will serve five-year terms. The Annual Meeting Chair will serve a one-year term during which he/she will serve as the local host for the annual meeting of the Technical Committee.
Administrative Advisor: Dr. Gregory J. Weidemann
CSREES Representative: Dr. James V. Parchetti
Project Chair: Dr. Raghavan Charudattan
Project Secretary: Dr. John Lydon
Objective Chairs: 1A) Dr. Erin Rosskopf
1B) Dr. Raghavan Charudattan
1C) Dr. Raghavan Charudattan
1D) Dr. Douglas Boyette
1E) Dr. Joe Neal
2) Dr. Raghavan Charudattan
3) Dr. Erin Rosskopf
4) Dr. David Sands / Dr. Alice Pilgeram
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