|Yokomi, R. K.|
Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2003
Publication Date: 6/1/2004
Citation: Yokomi, R. K., Polek, M., Satar, S., Gottwald, T. R. 2003. A Sampling Protocol To Optimize Locating Citrus Tristeza Virus Reservoirs. International Organization of Citrus Virologist Proceedings. Interpretive Summary: Citrus Tristeza Virus (CTV) is a serious disease of citrus that is not easily diagnosed. With over 1.5 million acres of citrus in the United States and several million worldwide, finding trees infected with CTV that can be eradicated prior to disease spread is a daunting problem. The Central Florida Tristeza Eradication Agency (CCTEA) uses a sampling/survey method called the 'Hierarchical Survey = HS' developed by the third author for this purpose. This manuscript describes a modification to the HS method and a test of the to detect and estimate disease incidence in a large area that is considered a hot spot for CTV. The HS method was found to be an economical method to locate areas of highest CTV risk and prioritize these areas for more complete surveys.
Technical Abstract: In citrus-growing areas where the incidence of citrus tristeza virus (CTV) is low and CTV spread is suspected, a sampling strategy that maximizes limited resources and allows coverage of large areas is necessary to optimize detection of CTV reservoirs. Such a strategy was developed to estimate virus incidence over a large area by sub-sampling portions of orchards. An area of 1,036 ha of mostly contiguous sweet orange blocks was selected in Central California where isolates collected were readily transmitted by the cotton aphid in laboratory vector efficiency tests. This area was comprised of 79 commercial orchards ranging in size from 2 to 16 ha. Knowledge of the CTV status of all orchards existed from previous surveys conducted from the 1998-99 season to the present which used either hierarchical sub-sampling (HS) or singles survey (every tree) and ELISA. Each orchard was considered as a plot. Regardless of the orchard size or planting density, a subplot of 20 rows by 20 trees (400 trees total) or equivalent was selected in the center of each plot. Each subplot was then surveyed using the HS method and the results compared to HS surveys conducted over the entire orchard. The CTV incidence in most subplots was estimated to be zero to #1% of the trees. These results were comparable to previous HS surveys of the entire orchard. Several subplots had estimated infection levels of 3 to 5% which was also comparable to the previous full HS surveys. In some cases, however, the subplot HS either failed to detect CTV or under-estimated incidence. Therefore, the most appropriate use of the subplot HS is as an economical method to locate areas of highest CTV risk and prioritize these areas for more complete surveys.