CITRUS CANKER (CC): Xanthomonas axonopodis Starr & Garces emend. Vauterin, et al pv. citri (Hasse) Dye (Xac) Gammaproteobacteria/Xanthomonadales/Xanthomonadaceae

DISTRIBUTION: Asia to Japan, India, southern & central Africa, the Middle East, Pacific Islands, South America and the southeastern United States. CC has been eradicated from South Africa, Mozambique & the Fiji Islands. Detection triggers active eradication or containment programs in southeastern United States, Uruguay and Brazil.

DESCRIPTION: The causative organism is a rod-shaped bacteria (Fig 1 - aggregation grown in medium, bar = 5 µm). Laboratories can isolate and culture the bacteria that stream from the edges of thinly cut lesion sections. Colonies on agar plates are circular, convex, semi-translucent and yellow.

HOSTS:Citrus (grapefruit, lime etc.), Poncirus (trifoliate orange, etc.), Fortunella (kumquat), and a few other Rutaceae.

DAMAGE: The pathogen causes necrotic (dead cells) lesions on leaves, stems and fruit (Fig 2). Severe infections can cause defoliation, badly blemished fruit, premature fruit drop, twig dieback and general tree decline. Scarred fruit looses market value. Monetary losses from quarantine actions are significant.

INSPECTION TIPS: Walk the rows of the citrus grove, look carefully from top of tree canopy to bottom of tree canopy for the circular, yellow halos on leaves. Usually more than one lesion is apparent. Examine all ages of foliage from the newest flush to the older leaves. Use a magnifying lens to examine center of lesion for broken, scabby tissue and volcanic (raised center) with water-soaked margin (Fig 3 - leaf top, Fig 4 - leaf bottom). The yellow hallows do not show on infected stems although they may be present on fruit (fruit lesion may develop sunken center). You may also notice lesions on stems (Fig 5 - young lesions on a grapefruit stem, Fig 6 - older lesions on Key lime).

LIFE CYCLE : Citrus canker bacteria can enter through the plant's stomatal openings (pores in the surface of leaves through which air normally enters the leaves) or through wounds to leaves or other green portions of the plant. In most cases, younger leaves are considered to be the most susceptible. Also, damage caused by citrus leaf miner larvae can be particularly good sites for infection to occur. Wind, rain & contaminated hands & equipment can spread CC. Once infection occurs, it may take from 14 to sixty or more days for symptoms to appear. Citrus canker bacteria can stay viable in old lesions or other plant surfaces for several months.

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