NCDC204: Biological Control of Plant Pathogens in the North Central Region (NC125)
- October 01, 2004 to September 30, 2006
- Administrative Advisor(s):
Steven G. Pueppke
- NIFA Reps:
Statement of Issue(s) and Justification:Plant pathogens cause diseases that dramatically impact the yield and quality of crops produced in the North Central region. Management of these diseases is limited due to a variety of environmental and economic constraints. Effective biological control strategies can provide useful options for integrated pest management. This project addresses the interactions of applied and resident microorganisms with plant pathogens and their host plants within the varied environments of the region. The ultimate objective is to develop biologically-based disease management strategies that maximize the benefits of applied and resident microbial agents.
Pathogens that cause the most significant diseases on agronomic and horticultural crops are widely distributed across the North Central region. These pathogens are phylogenetically diverse (e.g. various prokaryotes, oomyctes, fungi, and nematodes) and predominantly opportunistic, attacking plants when conditions are conducive to disease development (Agrios, 1997). While the spectrum of destructive diseases varies annually, important genera of pathogens (e.g. Bipolaris, Colletotrichum, Fusarium, Heterodera, Phialophora, Puccinia, Pythium, Phytophthora, Rhizoctonia, and Sclerotinia) are endemic to the North Central region. There, and throughout the United States, these pathogens present a perennial problem that has to be managed properly for optimum productivity. In large fields, multiple diseases are often present, and this complex of diseases can result in substantial yield losses. For example, a recent study by Nutter et al. (2002) showed that the average yield loss in alfalfa due to foliar diseases could exceed 19% and that over 50% of the variance in yields could be attributed to plant diseases. In the North Central region, the yield losses caused by these plant pathogens is estimated to be worth several billion dollars, despite the current disease control efforts. For example, soybean farmers in the North Central region lose approximately 6.8 million tons each year in yield (valued at $1.475 billion) to soilborne plant diseases alone (Wrather et al., 2003). Effective disease management strategies are needed to minimize the economic damage to the major field crops of the North Central region.
The destructive activities of soilborne and residue-borne pathogens can be limited by a variety of farming practices, including crop rotation, tillage, and/or seed-treatment fungicides (Hoeft, 2000). These practices reduce disease by removing the host (rotation), damaging or displacing the pathogen (tillage), and avoiding the optimum growth conditions of the pathogen (based on planting date or planting density). Fundamentally, the management of crop residues and organic matter plays a key role in the control of root diseases (Bockus, 1998; Hoitink, 1999). Even so, a number of environmental variables, including climate and edaphic factors, can impact the rotation effect (Porter, 1997). While many root pathogens are generally crop-specific (e.g. for either corn or soybeans), some soilborne pathogens are virulent on multiple crops (e.g. Zhang and Yang, 2000). Chemical fungicides (e.g. mefonoxam and fludioxonil) can be used to suppress pathogen activity in the seedbed (Hoeft, 2000). Although seed treatment fungicides are used in the vast majority of corn and wheat plantings and are generally effective at promoting seedling emergence and vigor (especially in corn), chemical seed treatments do not provide season-long protection from soilborne pathogens and, therefore, yield responses are not consistently observed with their application (Lipps, 2001). Applications of chemical fungicides in urban landscapes (e.g. on golf courses and lawns) can be substantial but elevate concerns about negative impacts on water quality and human health (Vargas, 1994). Successful application of biological control organisms requires more knowledge-intensive management (BCWG, 1998), including a greater understanding of the environmental and economic issues influencing effective biopesticide use in a variety of agricultural systems.
Biological control agents, i.e. organisms antagonistic to plant pests and pathogens, can be used to reduce the incidence and severity of root diseases (Handelsman and Stabb, 1996; Cook and Baker, 1983), and foliar diseases (gb refs ). Phylogenetically diverse microorganisms have been used as biocontrol agents (EPA, 2003), but only a small fraction of isolates from named genera have significant biocontrol activity. The mechanisms by which these microbial agents suppress diseases include antibiosis, parasitism, competition, and induction of host resistance (Cook and Baker, 1983). Some agents may use multiple mechanisms to suppress disease. For example, Lysobacter enzymogenes has been shown to secrete chitinases, which may degrade fungal cell walls and subsequently induce plant host defenses (Kilic-Ekici, 2003; Zhang and Yuen, 2000). While sometimes perceived as less reliable or less effective than chemical alternatives, several microbial biocontrol agents have proven useful in multiple applications (Harman, 2000). This success is reflected in the fact that over two dozen biocontrol products are currently being marketed to producers (McSpadden Gardener and Fravel, 2002). Numerous studies have shown that biological controls can be used alone or in combination with chemicals to successfully increase stands and/or yields of a diversity of crops. However, many years of research have shown that microbial biological control agents do not perform consistently under all field conditions. The causes of inconsistent performance of biocontrol agents are not well understood, but likely are rooted in the complex interactions between microorganisms, plant hosts, and the abiotic environment that lead to biological control.
In conventional agriculture, trends toward decreasing the frequency and types of rotations, reducing tillage, and reducing pesticide inputs all increase the potential for crop losses to plant diseases. Indeed, long-term research plots in the Midwest indicate that the omission of either tillage or rotation can reduce corn yields by 8% and soybean yields by up to 20% (Crookston et al., 1991; Hickman and Medlin, 2001, Porter et al., 1997). In addition, organic farmers need environmentally-friendly and socially-acceptable disease control practices. In all types of systems, augmentative biological control strategies hold promise for improving production efficiency. Indeed, biological controls of plant pests and pathogens have been targeted for development as part of integrated pest management (IPM) programs, and they are expected to play a key role in sustainable agriculture in the future (Jacobsen 1997). Microbial biological control agents are generally understood to be less toxic and, potentially, less costly than chemical fungicides, thus these agents can play a major role in the development of sustainable agricultural systems. There is a growing demand for sound, biologically-based pest management practices. Recent surveys of both conventional and organic growers indicate an interest in using biocontrol products (van Arsdall and Frantz, 2001; Rzewnicki, 2000), suggesting that the market potential for biocontrol products will increase in coming years.
Continued prospecting for new biological control agents is required to diversify the potential applications of biocontrol, identify more effective agents, and replace commercialized biocontrol products should resistance develop. The successful identification of candidate biocontrol agents requires effective screening procedures. Previous screening programs have yielded numerous candidate organisms for commercial development (Cook and Baker, 1983). The success of all subsequent stages of developing biocontrol strategies depends on the ability of a screening procedure to identify appropriate candidate agents. Conventional screens for new biocontrol microbes are still useful (e.g. Bull et al., 2002, Michaud et al. 2002); however, new techniques can enhance our ability to screen for effective biocontrol agents. For example, application of molecular markers for biocontrol activities will facilitate screening for locally adapted biocontrol strains (Landa et al., 2002, Raaijmakers and Weller, 2001).
Funding for basic and applied research continues to be provided by the USDA's Cooperative Research, Education, and Extension Service through a variety of programs (eg. the National Research Initiative (NRI), and the Pest Management Alternatives Program (PMAP)) as well as internally within the Agricultural Research Service. Such investment will ensure that innovations in biological control research will continue. An upswing in commercial interests has also developed in the past few years, and prospects for increased growth are positive. The Biopesticide Industry Alliance has formed, and it is now actively promoting the value and efficacy of biopesticides, including those that control plant pathogens. Clearly, the future success of the biological control industry will depend on innovative business management, product marketing, extension education, and research (BCWG, 1998; Mathre et al., 1999).
A variety of research questions remain to be answered about the nature of biological control and the means to most effectively manage it under production conditions. Advanced molecular techniques are now being used to characterize the diversity, abundance, and activities of microbes that live in and around plants, including those that significantly impact plant health. Such investigations include the characterization of the activities of biocontrol agents (Zhou, 2002; Kobayashi, 2002). Much remains to be learned about the microbial ecology of plant associated microorganisms in different agricultural systems (Weller et al., 2002). Recent advances in this area have led to a greater understanding of colonization of both roots and shoots of crop plants (Beattie and Marcell, 2002; McSpadden Gardener, 2002). Fundamental work is needed on characterizing the mechanisms by which organic amendments reduce plant disease (Nelson and Boehm, 2002). Studies are needed on the practical aspects of integrating biocontrol strategies with other farm practices (e.g. Dodds, 2002; Windels, 2002) and on how to make new biocontrol products stable, effective, safer and more cost-effective. Ecological models can be applied to identify the required characteristics of biocontrol agents and the stages in pathogen life cycles at which they are most readily managed via biological control (e.g., Garrett and Bowden, 2002). To better evaluate the costs and benefits of using biological control strategies, plant disease and associated biocontrol sub-models, akin to those developed for crop physiology (Gage, 2002), need to be developed. Computer models may be useful in determining the severity and occurrence of various plant diseases and the utility of various biocontrol strategies at expanded scales over large time frames (Safir, 2002). A greater understanding of the ecology, physiology and genetic variation of biocontrol agents, their methods of application, and their interactions with pathogens, hosts, and the environment is necessary before there is widespread commercial-scale use of biocontrol in U.S. agriculture.
Regional cooperation among scientists working on biocontrol can advance knowledge on how to use this important technology. Sharing of biocontrol agents and testing on various crops under a wide range of environments and soil types is one type of cooperation. Another is the development of techniques for producing, storing, and delivering biocontrol agents. The standardization of protocols for testing is an important result of cooperation. Regional cooperation also provides important a forum for discussions in which results and ideas can be exchanged and debated and cooperative efforts are enhanced and broadened.
In this five year project, we will build on the past success of cooperative efforts on biocontrol in the North Central Region. Working collaboratively, we will systematically compare the efficacy of biocontrol products on economically important plant species and characterize the mechanisms of biocontrol systems. Research across the North Central region will allow us to characterize the factors that influence the effectiveness of biocontrol systems and develop strategies for enhancing the activity of applied and indigenous biocontrol agents. Through such collaborative research and scientific exchange, we will foster the development of new ideas and approaches for biological control. The results and accomplishments of this project will have direct application to the use of biocontrol to protect economically important plants from a variety of plant pathogens.
Procedures and Activities
Expected Outcomes and Impacts:
Project Participation:Include a completed Appendix E form
s:/Steven G. Pueppke
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