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 horticul tural holdings at Lambell's Lagoon in 1992 failed to detect symptoms o f citrus canker. Leaf washings from trees in each orchard failed to de tect,X. c. citri using leaf enrichment or immunofluorescence technique s. Other xanthomonad isolates were obtained and these produced a sligh t 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 1 991 outbreak site. This outbreak was confirmed as Group A of X. c. cit ri on the basis of pathogenicity tests, fatty acid analyses of recover ed bacteria, immunofluorescence microscopy and by genomic DNA fingerpr inting.