A further outbreak of citrus canker near Darwin

Citrus canker (caused by Xanthomonas campestris pv. citri Group A) was detected in a pummelo orchard at Lambell's Lagoon near Darwin in 1991. All citrus trees in the orchard were eradicated. Surveys of horticultural holdings at Lambell's Lagoon in 1992 failed to detect symptoms of citrus canker. Leaf washings from trees in each orchard failed to detect X. c. citriti using leaf enrichment or immunofluorescence techniques. Other xanthomonad isolates were obtained and these produced a slight callusing with watersoaking around wounds made in detached leaves of Duncan grapefruit. In 1993, canker symptoms were observed on lime and grapefruit twigs and fruit in a mixed citrus orchard 500 m from the 1991 outbreak site. This outbreak was confirmed as Group A of X. c. citri on the basis of pathogenicity tests, fatty acid analyses of recovered bacteria, irnmunofluorescence microscopy and by genomic DNA fingerprinting.