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First report of Xanthomonas cucurbitae causing bacterial leaf spot of watermelon in the Seychelles

Pruvost O., Robène-Soustrade I., Ah-You N., Jouen E., Boyer C., Wuster G., Hostachy B., Napoles C., Dogley W.. 2009. Plant Disease, 93 (6) : p. 671-671.

Bacterial leaf spot of cucurbits caused by Xanthomonas cucurbitae (4) can be a harmful disease of several cucurbit species in tropical environments, mainly within the Cucumis, Cucurbita, and Citrullus genera. The bacterium induces angular, water-soaked leaf spots, which sometimes become necrotic and have a chlorotic halo. Scab-like lesions on fruit can also be observed (2). Water-soaked, angular leaf lesions were collected from approximately 15 watermelon plants (Citrullus lanatus) in a production field located in Mahé, Seychelles in 2003. Yellow-pigmented Xanthomonas-like bacterial colonies were isolated on KC semiselective medium (yeast extract 7 g, peptone 7 g, glucose 7 g, agar 18 g, distilled water 1,000 ml, propiconazole 20 ?g ml-1, cephalexin 40 mg liter-1, and kasugamycin 20 mg liter-1) from all isolation attempts (3). Amplified fragment length polymorphism (AFLP) analysis was performed on four watermelon strains together with reference strains of Xanthomonas cucurbitae (LMG 690 [type strain] and LMG 8663) and the type strain of all other valid Xanthomonas species using SacI/MspI and four primer pairs (unlabeled MspI + 1 [A, C, T, or G] primers and 5?-labeled - SacI + C primer for the selective amplification step) (1). The four strains from watermelon showed identical fingerprints and were most closely related to X. cucurbitae. One strain from diseased watermelon (JZ88-1) was further analyzed by MultiLocus Sequence Analysis (MLSA) using portions of three housekeeping genes (atpD, dnaK, and gyrB) as described previously (1). This strain displayed a very high relatedness (99.8 and 98.9% with strain LMG 690 and LMG 8663, respectively) to the two reference strains of X. cucurbitae. AFLP and MLSA were useful for identifying strains at the species level that were consistent with previous results (1). Bottle-gourd (Lagenaria siceraria), pumpkin (Cucurbita maxima), squash cv. Aurore (Cucurbita pepo), cucumber cv. L-04 (Cucumis sativus), cantaloupe melon cv. Cezanne

Mots-clés : xanthomonas; citrullus lanatus; seychelles; xanthomonas cucurbitae

Thématique : Maladies des plantes

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