First report in Thailand of Xanthomonas axonopodis pv. citri-A* causing citrus canker on lime

Bui Thi Ngoc Lan, Vernière Christian, Pruvost Olivier, Kositcharoenkul N., Phawichit S.. 2007. First report in Thailand of Xanthomonas axonopodis pv. citri-A* causing citrus canker on lime. Plant Disease, 91 (6), Résumé : 771.

https://doi.org/10.1094/PDIS-91-6-0771A

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Résumé : Asiatic citrus canker, caused by Xanthomonas axonopodis pv. citri (Xac-A), is a bacterial disease of economic importance in tropical and subtropical citrus-producing areas. Xac-A can cause severe infection in a wide range of citrus species and induces erumpent, callus-like lesions with a water-soaked margin. Severe attacks cause premature fruit drop and twig dieback. It has consequently been submitted to eradication efforts and international regulations. Recently, a group of strains with a host range restricted to Mexican lime (Citrus aurantifolia), but not infecting grapefruit (C. paradisi) known to be very susceptible to Xac-A, was described in different areas of southwest Asia, including Saudi Arabia, Oman, Iran, and India (3). Phenotypic and genetic similarities with Xac-A designated it as a variant called X. axonopodis pv. citri-A*. A variant with a similar restricted host range, designated X. axonopodis pv. citri-A, was also detected in Florida and likely originated from India (2). Amplified fragment length polymorphism (AFLP) analysis of 26 isolates from Thailand and additional reference isolates from Xac-A, -A*, -A, and X. axonopodis pv. aurantifolii (2,3) using SacI/MspI and four primer pairs (unlabeled MspI + 1 [A, C, T, or G] primers and 5(prime)-labeled SacI + C primer for the selective amplification step), separated the Thai isolates into two distinct groups. A group composed of 20 isolates from different citrus species, including five isolates from lime, was closely related to strains with a large host range and previously identified as Xac-A. A second group, solely composed of six isolates from lime, was genetically related to Xac-A*. All Thai isolates were collected before 1991. Isolates genetically closed to Xac-A* originated from the central and northern provinces, whereas isolates related to Xac-A originated from all sampled provinces. On the basis of AFLP, no Thai isolate was related to X. axonopodis pv. aurantifolii. A specific X. axonopodis pv. citri nested-PCR assay (1) produced the expected fragments for all Thai isolates. Mexican lime leaves inoculated with Thai isolates of Xac-A and Xac-A* using a detached leaf assay (3) showed typical canker symptoms 1 week after inoculation. When inoculated to grapefruit or sweet orange, the Thai isolates genetically related to Xac-A* by AFLP analysis did not induce any canker symptoms, while isolates related to Xac-A produced canker symptoms on these two citrus species. In Thailand, Xac-A* induced severe symptoms on lime trees, including extensive defoliation and numerous twig cankers that often developed as diebacks. The Xac-A* variant appears epidemiologically important on lime, consistent with previous reports from southwest Asia. The detection of Xac-A* in Thailand makes it necessary to evaluate its geographic distribution in southeast Asia. (Texte intégral)

Mots-clés Agrovoc : lime, Citrus, maladie des plantes, Xanthomonas, agent pathogène, identification, distribution géographique, Xanthomonas campestris citri

Mots-clés géographiques Agrovoc : Thaïlande

Mots-clés complémentaires : Xanthomonas axonopodis pv. citri

Classification Agris : H20 - Maladies des plantes

Champ stratégique Cirad : Axe 1 (2005-2013) - Intensification écologique

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