|Bassanezi, R. B.|
|Busato, L. A.|
Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2005
Publication Date: 3/18/2005
Citation: Bassanezi, R., Busato, L., Bergamin-Filho, A., Amorim, L., Gottwald, T.R. 2005. Preliminary spatial pattern analysis of huanglongbing in sao paulo, brazil. International Organization of Citrus Virologists Proceedings. Interpretive Summary: Citrus Huanglongbing (Chinese for yellow dragon disease)is considered by the majority of citrus researchers to be the worst disease of citrus worldwide causing major production losses and eventually death of the infected trees. The disease is vectored by an insect that occurs in Florida and Texas but to date the disease does not occur in the US. This past year it was discovered in the western hemisphere for the first time in Sao Paulo Brazil. A new isolate of the bacteria that causes the disease was discovered by Brazilian and French researchers. This study is the first description of the epidemiology of the disease in Brazil, that is, how it increases and spreads. The analysis also included an analysis of the possible interaction of the insect that occurs in Brazil and is implicated as a vector. This work builds on prior work of the fifth author who was the first to describe the epidemiology of the disease in China, the Philippines, and Taiwan. The study also delimited the infection in Brazil and will serve as the basis of information needed to evaluate the possibility of success of an eradication program to rid Brazil of the disease.
Technical Abstract: Huanglongbing (HLB) was reported in 2004 in São Paulo, Brazil. Assessments of diseased trees by visual symptoms were made in 36 groves from 8 farms in the Central citrus region of São Paulo State. 155 HLB spatial maps (varying from 0.14 to 25.99% of disease incidence) were analysed, considering quadrat sizes of 2x2, 4x4, 6x6 and 8x8 trees, by the ordinary runs analysis, the binomial index of dispersion and the binary form of Taylor's power law. Aggregation among HLB-symptomatic trees was detected by ordinary runs analysis, with clustering existing in both within- and across-rows directions. However the percentage of aggregation within- and across-rows was low. The binomial index of dispersion for various quadrat sizes suggested aggregation of HLB-symptomatic trees for about 40% of the plots. The relationship between log(observed variance) and log(binomial variance) was highly significant for all four quadrat sizes. Estimated parameters of the binary form of Taylor's power law provided an overall measure of aggregation of HLB-symptomatic trees for all quadrat sizes tested. All estimates of B and A, were statistically different from 1, which indicated a general and significant pattern of aggregation of symptomatic plants for all quadrat sizes tested. The degree of aggregation was also positively related to disease incidence. Data from 20 plots ranging in disease incidence were also analyzed by spatial autocorrelation to examine the association among groups of infected trees using the 2x2 quadrat size. In 14 of 20 cases, clusters of HLB-infected trees were found to be associated with secondary clusters whose centers were at distances ranging from 4.2 to 22.1 tree spaces distant, indicating psyllid vector movement resulting in transmission both to nearby trees causing clusters and to trees at considerable distance initiating new foci of infection.