Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 24, 1998
Publication Date: N/A
Interpretive Summary: Citrus tristeza virus (CTV) is one of the most destructive diseases of citrus worldwide. The virus is transmitted by aphids. The most efficient vector of CTV is the brown citrus aphid, which was recent introduced into Florida in November 1995. This study contains data from research plots located in Costa Rica and the Dominican Republic that demonstrates and explains the affects that the brown citrus aphid has on CTV increase and spread and compares it to previous publications where other less effective aphid vectors were involved. This information will be used in the US to help regulatory agencies and growers to better understand and prepare for increased economic loses due to CTV. It was found that CTV increase 3 to 4 times faster in the presence of the brown citrus aphid. It was also found that CTV infected trees tend to be in aggregates or groups in a grove when the brown citrus aphid is present whereas, CTV infected trees were much more widespread when the aphid was absent and spread was due to other aphid species. Such basic information on the study of aphid dynamics and their effect on CTV increase and spread will be used in future studies to help develop control strategies to lessen the effect of the brown citrus aphid on CTV associated losses.
Technical Abstract: Citrus tristeza virus (CTV) was monitored for 4 years by monoclonal antibody probes via ELISA in four citrus orchards in northern Cost Rica and four orchards in the Dominican Republic following the introduction of the brown citrus aphid, Toxoptera citricida. Ordinary runs analysis failed to show a spatial relationship of disease status among immediately adjacent trees. The beta-binomial index of dispersion for various quadrat sizes suggested aggregations of CTV-positive trees for all plots. Spatial autocorrelation analysis of proximity patterns suggested that aggregation often existed among quadrats of various sizes up to four lag distances. Some asymmetry was also detected for some spatial autocorrelation proximity patterns. These results were interpreted to mean that although CTV-positive trees did not influence immediately adjacent trees, virus transmission was common within a local area of influence that extended two to eight trees in all directions. The spatial and temporal analyses gave some insight into possible underlying processes of CTV spread in the presence of T. citricida and suggested CTV spread was predominantly to trees within a local area. Longer distance spread probably exists but may well be of a complexity beyond the detection ability of the spatial analysis methods employed or perhaps on a scale that is larger than the dimensions of the plots studied.