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A View From ScienceWhen Walton Cook first approached me to discuss his book about the development of plant pathogens for use as control agents against unwanted plants, it seemed very natural to me. I knew that one of the problems with evasive plants was that they often were moved without their limiting pathogens or pests. The other side of the coin is where new pathogens or pests were introduced to new native hosts. Either way, ecological disasters resulted, as shown by the loss of the American Elm trees by Dutch elm disease and the chestnut trees killed by Chestnut blight. These situations occurred when the casual agents were introduced into North America on imported logs. These incidents show that plant pathogens are capable of wiping out a plant species and can remain effective for a long period of time. Spread and adaptation to nonhost plants is of concern and must be considered when developing pathogens for use as a biocontrol agent. However, there are situations where evidence supports the stability of the host ranges of certain pathogens, thus allowing their use as biocontrol agents. For example, the development of tomato varieties resistant to Fusarium wilts. These were first selected in 1910 and 1920, and are still resistant to Fusarium oxysporum. The original selections are still being used for breeding stock. Bacterial wilt of alfalfa caused by Clavibacter michiganense, subsp. insidiosum, was a serious problem until the 1970s when resistant varieties were released. Today the disease is rarely, if ever, observed. The tobacco plants developed in the 1940s and peanut plants in 1920, both resistant to bacterial wilt caused by Ralstonia solanacearum, are still used as a source of resistance, and support that both the host and the pathogen are quite stable. This suggests that this pathogen would be safe to use as a biocontrol agent. In the scientific world, there is interest in the use of pathogenic bacteria to control plant pests. A cooperative regional research project, S-268 Evaluation and Development of Plant Pathogens, have been investigating several plant pathogens for possible weed control agents. Among them, Psuudomonas syringae pv. Tagetis and Ralstonia solanacaerum have been used in field trials on their specific weed host. In these trials, the pathogens were effective as weed control. Plants of other species were tested and were not susceptible under the conditions used. The fact that this type of an approach (using plant pathogens to control the source of a drug) may have risks outside the normal ones encountered doing field research was demonstrated when a long term project investigating the use of plant pathogens to control marijuana plants was canceled by a university administration. When the program was made public, the university administrator was concerned about possible retribution from drug war lords in a producing country. It is of interest that publicity of this research program was the result of a lawsuit brought about by one of the state chapters of the National Organization for the Reform of Marijuana Laws. Thus, while Walton Cook's story told in BUZZWORD is fiction, it is based on scientific facts. Felix L. Lukezic
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