ISHS Acta Horticulturae 823: XI International Symposium on the Processing Tomato
ASSAYS FOR SEEDBORNE BACTERIA: WHAT THEY CAN AND CAN'T DO |
| Author: | M.L. Gleason |
| Abstract:
Major bacterial diseases of tomato, including bacterial spot, speck, and canker, can be transmitted via infested seeds to seedlings, sometime resulting in epidemics in processing tomato production fields. Laboratory assays designed to detect these pathogens on seeds are a mainstay of the tomato industry, but they do not always detect the target pathogens. The result can sometimes be crop failures and lawsuits between growers and seed companies. Given the economic importance of assays for seedborne bacterial pathogens, it is worthwhile to review the challenges of detecting target bacteria in seed lots, the criteria for determining which assay is most reliable, and ways in which seed assays could be improved in the future. In the past, evaluating the relative merits of seed assays for bacterial pathogens has been mired in anecdotes and hampered by a lack of critical analysis. Fortunately, this picture is beginning to change as assay protocols become more standardized at laboratories around the world. It is helpful to think of seed assays in terms of contingency table analysis. This type of analysis was first used to evaluate the accuracy of medical diagnoses, but it also adapts well to detection of seedborne pathogens. Any seedborne pathogen assay has basically four types of outcomes: true positive, true negative, false positive, and false negative. The “true” outcomes are those in which the assay correctly determines whether a target pathogen – for example, Clavibacter michiganensis subsp. michiganensis - is present (true positive) or absent (true negative) in the seed lot from which the tested sample was taken. The “false” outcomes are the errors; false positive results are those in which the test indicated presence of the target pathogen but it was not actually there, and false negative results are those in which no detection was reported in a lot that did actually contain the pathogen. Each kind of error has characteristic potential consequences: false positives may lead to rejection of a lot for sale or export, whereas false negatives may lead to crop failures and/or lawsuits. Seed assays strive to maximize the “true” outcomes and minimize the “false” ones. | |
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