A comprehensive analysis of the Asiatic citrus canker eradication programme in Sao Paulo state, Brazil, from 1999 to 2009

Asiatic citrus canker (ACC), caused by Xanthomonas citri subsp. citri, has been controlled by exclusion and eradication measures in Sao Paulo state (SP), Brazil, since it was first detected in 1957. Several protocols of eradication have been used since then, but the protocol applied from 1999 to 2009 was the most successful and well documented of these. During that time, if the incidence of trees with symptoms in a citrus block was <= 0.5%, the infected trees and the symptomless trees within a 30 m radius were removed. However, if the incidence was >0.5%, the entire block was eliminated. Subsequently, inspections were carried out to monitor the affected blocks during quarantine. Although this protocol did not eliminate the disease from SP, it suppressed the incidence of affected blocks to very low annual levels (<0.20%) for a decade. Of over 5000 foci detected, 65.1% were eliminated by removing the block, either when disease was first detected (47.8%) or at a subsequent detection (17.3%), and 28.4% were eradicated by removing trees within a 30 m radius. The latter method was not an effective stand-alone measure for ACC eradication and the 0.5% threshold was the key factor in suppression of disease statewide. Currently, a re-emergence of ACC is occurring in SP. The information presented here will aid the establishment of protocols for the eradication of ACC in other citrus-growing areas with low incidence of the disease or at risk of pathogen introduction.