Author
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HUGHES, GARETH - UNIVERSITY OF EDINBURGH |
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Gottwald, Timothy |
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Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/11/2001 Publication Date: N/A Citation: N/A Interpretive Summary: Citrus tristeza virus is one of the most destructive viral diseases of citrus and causes considerable damage to US citrus production areas each year. Survey methods have been developed by the authors over the past few years to detect low levels of citrus tristeza virus in commercial citrus groves. These have been adopted for use by various citrus producing states and regulatory agencies in the US as well as Caribbean, Central American and South American counties who have chosen to survey for severe CTV strains to identify their location and level of infestation for eradication or management. To date however, no survey method has been developed for rapid and efficient survey of citrus nurseries prior to distribution to commercial growers. This is a vital first step to allow establishment of a nursery certification program to protect the industry from distribution of disease through plant material. This paper describes the development and theory behind a new survey method for citrus nurseries. The method was validated by both analytical means and computer simulation. The method will be given to state and federal regulatory agencies to deploy. Although developed for citrus, the new survey method will likely be adaptable to other commodities, crops and survey situations as well. Technical Abstract: Monitoring of plant health takes place in citrus nurseries, in an attempt to prevent the distribution of infected plants from nurseries to commercial groves. In this article, both analytical and simulation methods are used to characterize schemes by which such monitoring can be carried out, in the particular context of citrus tristeza virus infection. The inclusiveness of a sample is an assessment of the degree of redundancy that occurs because, in some samples, daughter plants that are among the progeny of identically-infected propagation material may appear more than once. The operating characteristic function shows the probability of reaching a decision, based on sampling, that a population of daughter plants has an incidence of infection less than or equal to some adopted threshold level, for any actual level of incidence in the population. If the same percentage sampling rate is kept while the population size changes, both the inclusiveness and the operating characteristic function change. However, sample sizes may be calculated so that a specified operating characteristic function is maintained as population size varies. The sample sizes required to meet the conditions specified on the operating characteristics do not increase in proportion to population size. Thus fewer samples might need to be taken from large populations of daughter plants than would be the case if a constant percentage sampling scheme were adopted. |
