W147: Managing Plant Microbe Interactions in Soil to Promote Sustainable Agriculture
Statement of Issues and Justification
STATEMENT OF THE PROBLEM:The use of microbes to control plant disease and enhance crop production is desirable for the following reasons: 1) chemical pesticides are being severely restricted; 2) the public is demanding reduced pesticide use; 3) resistance to biocontrol organisms is unlikely to develop; 4) biocontrol organisms are selective in their mode of action;5) biocontrol organisms have little effect on other beneficial organisms; 6) biocontrol organisms are biodegradable; 7) biocontrol organisms pose little danger to humans or animals; and, 8) many biocontrol methods improve the soil and enhance the sustainability of agriculture.
While a number of biocontrol agents are now available commercially, problems with production, storage, delivery, reliability, efficacy, establishment and understanding mechanisms of action have prevented most biocontrol products for plant disease control from becoming established in mainstream agriculture. We believe that tremendous progress has been made in the field of biological control of plant disease in the past five years and the W-147 project has been a major contributor to this progress. Because the results of our efforts are just coming to fruition , we feel it is prudent to continue the W- 147 project for another five years in an effort to improve and further stimulate the use of biocontrol organisms in agriculture.
JUSTIFICATION:
Soilborne plant pathogens are responsible for many acute and chronic diseases of crop plants that can result in severe losses for growers. Economic losses to soilborne pathogens are estimated at 50-75% of the attainable yield for many crops. Yield failures resulting from acute diseases such as vascular wilts, take-all of cereals, Phymatotrichum root rot, Verticillium and Phytophthora may be even more severe and have destroyed entire agriculture industries. About 90% of the 2000 major diseases of the principle crops in the US are caused by soilborne plant pathogens (Lewis and Papavizas, 1991). It has been estimated that the monetary losses to soilborne diseases is in excess of $4 billion /year (Lumsden et al., 1995).
While many soilborne diseases have been controlled, in part, by use of chemical pesticides, alternatives to the use of chemicals would be of value. Plant associated microbes used as biocontrol agents can play a role in reducing losses to such diseases, thus assuring a more sustainable agriculture and the long term ability of our land to produce food. Even when we were able to use pesticides freely, soilborne diseases were often ineffectually controlled and resulted in crop losses of $4 billion/year. Because of the difficulty in accessing the soilborne organisms in their chemically and physically diverse soil habitat, these organisms are notoriously difficult to control using traditional methods.
Soilborne diseases cause by Phytophthora, Verticillium and Faisarium remain major problems after more than 100 years of study. Soilborne pathogens are well adapted to soil conditions, and once established are very difficult to eliminate by any known method of control. Chemical control, when available, is often too expensive to be economically practical.
Although breeding for plant resistance to soilbo ne diseases holds much promise, the broad host range and large genetic variability of any soilborne pathogens makes plant resistance an incomplete method for disease control.
Biological control is- therefore one of the best ptions for management of soilborne diseases at a time when chemical alternatives are drastically being reduced (Baker and Cook, 1974; Cook, 1993; 1990; Cook and Baker, 1933; Jacobsen and Backman, 1993; Lewis and Papavizas, 1991; Weller, 1933; Whips, 1992) for the following reasons.
Biocontrol of soilborne pathogens are: 1) non-polluting and biodegradable, 2) relatively harmless to humans, 3) difficult for pathogens to develop resistance against, 4)selective in their mode of action, 5) unlikely to harm o her beneficial microorganisms, and 6)contribute toward improved soil conditions and t e sustainability of agriculture.
Great strides have been made recently in the field of biocontrol of soilborne plant pathogens. Progress and success has been docu ented in the review by Cook (1990).
Much of this success is due to activities of the members of W-147 (Cook 1990, Becker and Schwinn, 1993, Schroth and Becker, 1990, W eller, 1933). Today the EPA lists more than 24 commercial biocontrol agents which are registered and commercially available in North America. Nearly all of them have been registered during the past five years.
Interest and enthusiasm about biocontrol have never been greater. A recent analysis of articles published in 1996 in Phytopathologv, the premier plant disease journal in the US, shows that nearly 20% of the articles dealt with biocontrol. It appears that the W-147 regional project is both very timely and successful.
However, there remains a great deal left to be don in the field of biocontrol. Despite the promise, popular concept and public acceptance of biocontrol, few of the commercial biocontrol products are being used successfully i mainstream agriculture (Becker and Schwinn, 1993, Jacobsen and Backman, 1993, ipps, 1992). Many researchers believe we have yet to find the best biocontrol agents, sine they may inhabit remote areas where some of our soilborne pathogens arose. There are still major problems with cost, production, quality control, storage, stability, delivery , establishment, compatibility with agricultural practices, reliability, efficacy, slow effectivity, narrow host range and understanding of the life cycles and modes of action of biocontrol agents (Becker and Schwinn, 1993; Jacobsen and Backman; Lewis and Papavizas, 1991; Whipps, 1992).
Powell (1991) summarizes the current status of plant biocontrol agents when he says,"" the real problem for biological control is to deliver n active agent to the site where it is required and keep it there while activity is required."" We are yet unable to do that efficiently with most of our current biocontrol agents. Clearly there is much to be done in order to improve biocontrol agents so that they will become major factors in the control of soilborne diseases. Biocontrol agents isolated b participants of W-147 at ARS, CA-B, CA-D, CA-R, CO, ID, WA, IL, NM MT AK and NY have the ability to suppress a wide variety of plant pathogens that cause serious diseases of food, fiber and ornamental crops.
The need for ""high quality"" biocontrol agents has ever been more critical because of the pending loss of fungicides and fumigants upon which agriculture has been dependent for the last 50 years. Consider the billion-dollar-a-y ar commercial strawberry industry in California which relies exclusively on soil fumigation with a combination of methyl bromide and chloropicrin at about 250 lb/acre for disease, insect and weed control. The mandated 75% reduction in the use of methyl bromide by 2001 will leave this industry vulnerable to soilborne pests and pathogens.
Biocontrol may with great input from researchers provide a safe, environmentally sound alternative to methyl brornide and other valuable agricultural chemicals which may be lost in the future. The solutions to these problems require a large research input. No one person or single entity is capable of solving these problems. Much of the necessary research will require the interactive and cooperative efforts of a team. Cooperation between and among states, agencies, disciplines and basic and applied scientists is required. It is therefore logical to continue and encourage the successful interactions which are documented in the PROCEDURES section) of the W-147 regional project for another five years.
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