|Bassanezi, R. B.|
Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2004
Publication Date: 6/1/2005
Citation: Bassanezi, R.B., Bergamin-Filho, A., Amorim, L., Gottwald, T.R. 2005. Spatial and temporal analysis of citrus sudden death in Brazil. Proceedings of the International Organization of Citrus Virologists. Interpretive Summary: Citrus Sudden Death (CSD) is a disease of unknown cause that affects sweet orange grafted on Rangpur lime and Volkamer lemon in Brazil. The spread of the disease was was monitored in 116 citrus plots in 10 counties of Minas Gerais (MG) and São Paulo (SP) states, Brazil. Based an analysis of spread, many similarities were found between CSD and a virus disease of citrus call citrus tristeza virus (CTV) which is cause by an insect born virus of citrus. CSD appeared to spread and increase in exactly the same manor and with the same characteristics as CTV. Thus we formed the following hypothesis: Based on the symptoms and epidemiology of CSD, the disease is likely caused by a pathogen such as a virus and probably vectored by insects such as aphids. This is important because it defines how the disease will react to known control and mitigation procedures and enables us to predict crop and tree losses for forecasting of economic impact.
Technical Abstract: Citrus Sudden Death (CSD) is a disease of unknown etiology that affects sweet orange grafted on Rangpur lime and Volkamer lemon in Brazil. The spatial and temporal patterns of CSD was monitored in 116 citrus plots from 37 citrus farms located in 10 counties of Minas Gerais (MG) and São Paulo (SP) states, Brazil. Maps of the spatial distribution of CSD infected trees were examined at three spatial scales. At the lowest scale, ordinary runs analysis of CSD-symptomatic trees indicated a departure from randomness of symptomatic trees status among immediately adjacent trees both within rows and across rows. At the scale of small groups of trees, the binomial index of dispersion for various quadrat sizes suggested aggregation of CSD-symptomatic trees for almost all plots within the quadrat sizes tested. Also at the group scale, the index of aggregation increased with quadrat size. Estimated parameters of the binary form of Taylor's power law provided an overall measure of aggregation of CSD-symptomatic trees for all quadrat sizes tested and the intensity of aggregation was also a function of quadrat size and disease incidence. The final scale tested with at the entire plot level and the association among groups of CSD-affected trees. Spatial autocorrelation analysis of proximity patterns suggested that aggregation often existed among quadrats of various sizes up to three lag distances or three groups of trees distant. The number clusters of such groups that were indicated tended to decrease as CSD incidence increased.