Submitted to: Conference of International Organization of Citrus Virologists
Publication Type: Proceedings
Publication Acceptance Date: 12/13/2000
Publication Date: N/A
Interpretive Summary: Studies on the movement of citrus tristeza virus (CTV) under the influence of its efficient vector, the brown citrus aphid, are providing valuable insights for the US Citrus Industry. Some isolates of (CTV) are present in all commercial citrus production areas of the US. Distribution is limited in Arizona, California, and Texas, and the efficient aphid vector, the brown citrus aphid is not yet present. CTV is more widespread in Florida and movement has accelerated following the establishment of the brown citrus aphid in 1995. However, isolates of CTV that induce stem pitting in grapefruit and sweet orange are still rare in commercial citrus in Florida, and we do not know how far and fast these isolates could spread, once established. A long term epidemiological study on CTV in the Dominican Republic has recently revealed movement of new isolates of CTV in two separate locations. By using a combination of new and more efficient sampling techniques and molecular probes that can distinguish individual isolates, we have developed a system for looking on a local and regional scope at ingress of new isolates of CTV into areas that contain existing mild isolate infections. The data obtained should be highly applicable for projecting future scenarios in the US and for formulation of control strategies.
Technical Abstract: Following the establishment of the brown citrus aphid in the Dominican Republic, rapid diffusion of mild isolates of CTV into all major commercial citrus areas was observed between 1992 and 1995. Decline and stem pitting isolates were not detected initially, but since 1996, isolates that react to the monoclonal antibody MCA13 have been detected in several areas. An isolate causing decline in trees on sour orange rootstocks was discovered near Hato Mayor. An extensive survey of the area surrounding the original focus of infection of this decline isolate was conducted using a hierarchical sampling method. Increases in the area and the number of trees infected with decline isolates were documented. An isolate that severely affects Persian limes and causes stem pitting in grapefruit was also discovered in the Monte Plata area north of Santo Domingo. Biocharacterization tests and marker profiles using an immunocapture PCR protocol with selective primers indicated that this isolate is distinct from the decline-inducing isolate at Hato Mayor. While the mild isolate of CTV widely prevalent in the Dominican Republic appears similar to mild isolates from Florida, the MCA13-positive isolates discovered do not have the marker profile associated with the typical Florida decline isolate T36. Hierarchical sampling methods and genotype-specific probes are being used to determine rates and patterns of movement of CTV and the probable origin of the MCA13-positive isolates in new locations.