Detection and Characterization of a New Strain of Citrus Canker Bacteria from Key/Mexican Lime and Alemow in South Florida

Abstract

In the Wellington and Lake Worth areas of Palm Beach County, FL, citrus canker appeared on Key/Mexican lime (Citrus aurantiifolia) and alemow (C. macrophylla) trees over a period of about 6 to 7 years before detection, but nearby canker-susceptible citrus, such as grapefruit (C. × paradisi) and sweet orange (C. sinensis), were unaffected. Colonies of the causal bacterium, isolated from leaf, stem, and fruit lesions, appeared similar to the Asiatic group of strains of Xanthomonas axonopodis pv. citri (Xac-A) on the nutrient agar plate, but the growth on lima bean agar slants was less mucoid. The bacterium produced erumpent, pustule-like lesions of typical Asiatic citrus canker syndrome after inoculation into Key/Mexican lime, but brownish, flat, and necrotic lesions on the leaves of Duncan grapefruit, Madame Vinous sweet orange, sour orange (C. aurantium), citron (C. medica), Orlando tangelo (C. reticulata × C. × paradisi), and trifoliate orange (Poncirus trifoliata). The bacterium did not react with the Xac-A specific monoclonal antibody A1 using enzyme-linked immunosorbent assay (ELISA) and could not be detected by polymerase chain reaction (PCR)-based assays using primers selected for Xac-A. DNA reassociation analysis confirmed that the pathogen, designated as Xac-AW, was more closely related to Xac-A and Xac-A* strains than X. axonopodis pv. aurantifolii or the citrus bacterial spot pathogen (X. axonopodis pv. citrumelo). The strain can be easily differentiated from Xac-A and Xac-A* using ELISA, PCR-based tests, fatty acid analysis, pulsed-field gel electrophoresis of genomic DNA, and host specificity.

From Local Surveys to Global Surveillance: Three High-Throughput Genotyping Methods for Epidemiological Monitoring of Xanthomonas citri pv. citri Pathotypes

“…Earlier studies considered primarily the usefulness of PFGE, AFLP, or rep-PCR markers in terms of their abilities to determine genetic relationships between Xanthomonas pathovars that are pathogenic to citrus and X. citri pv. citri pathological variants (16,19,39,44,68).…”

“…Their distribution was initially reported to include Saudi Arabia, Oman, Iran, and India and was recently found to extend to southeast Asia, with reports of these strains in Thailand (10) and Cambodia (11). Finally, strains genetically related to pathotypes A and A* but able to infect Mexican lime and Citrus macrophylla naturally were recently detected in Florida and classified as a pathotype designated A w (68). The molecular basis of the specific interaction of X. citri pv.…”

“…The tools most often used for the molecular epidemiology of citrus canker have been repetitive-element-based PCR (rep-PCR) and pulsed-field gel electrophoresis (PFGE) (13,16,19,28,68). The lack of discriminatory power of rep-PCR and the high labor requirement for PFGE make it difficult to use these techniques extensively for outbreak investigations or regional or global surveillance (67).…”

Emended classification of xanthomonad pathogens on citrus

“…fuscans is differentiated from X. campestris pv. campestris by serology [27] and membrane protein analysis [16,28]. X. fuscans subsp.…”

Identification of New Genes Related to Virulence of <i>Xanthomonas axonopodis</i> Pv. <i>Citri</i> during Citrus Host Interactions

“…citri A* and A W , as well as X. fuscans subsp. aurantifolli strains B and C also cause citrus canker [4] [5] [6]. Their importance is attributed to their ability to infect only specific species of citrus, since they are restricted to certain regions in the world or vary considerably in their virulence induction profiles which are generally weaker than that observed for canker A.…”