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Characterization of a Variant of Xanthomonas citri subsp. citri that Triggers a Host-Specific Defense Response

First, second, fourth, fifth, sixth, and fourteenth authors: Instituto de Biología Molecular y Celular de Rosario (IBR)–Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Área Virología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 590, S2002LRK Rosario, Argentina; third author: Centro Internacional Franco Argentino de Ciencias de la Información y de Sistemas (CIFASIS), Blvd. 27 de Febrero 201 bis, S2000EZP Rosario, Argentina; seventh, eighth, ninth, twelfth, and thirteenth authors: Instituto de Tecnología Agroindustrial del Noroeste Argentino (ITA-NOA), Estación Experimental Agroindustrial Obispo Colombres (EEAOC)-CONICET, Av. William Cross 3150, Las Talitas T4101XAC Tucumán, Argentina; tenth author: Instituto de Ciencia y Tecnología Dr. Cesar Milstein, Fundación Pablo Cassará-CONICET, Saladillo 2468, C1440FFX Ciudad de Buenos Aires, Argentina; and eleventh author: Instituto de Biología Molecular y Celular de Plantas (IBMCP), Universidad Politécnica de Valencia-C.S.I.C, Ingeniero Fausto Elio, s/n. 46022 Valencia, España.

Citrus is an economically important fruit crop that is severely afflicted by Asiatic citrus bacterial canker (CBC), a disease caused by the phytopathogen Xanthomonas citri subsp. citri (X. citri). To gain insight into the molecular epidemiology of CBC, 42 Xanthomonas isolates were collected from a range of Citrus spp. across 17 different orchards in Tucumán, Argentina and subjected to molecular, biochemical, and pathogenicity tests. Analysis of genome-specific X. citri markers and DNA polymorphisms based on repetitive elements-based polymerase chain reaction showed that all 42 isolates belonged to X. citri. Interestingly, pathogenicity tests showed that one isolate, which shares >90% genetic similarity to the reference strain X. citri T, has host range specificity. This new variant of X. citri subsp. citri, named X. citri A^T, which is deficient in xanthan production, induces an atypical, noncankerous chlorotic phenotype in Citrus limon and C. paradisi and weak cankerous lesions in C. aurantifolia and C. clementina leaves. In C. limon, suppression of canker development is concomitant with an oxidative burst; xanthan is not implicated in the phenotype induced by this interaction, suggesting that other bacterial factors would be involved in triggering the defense response.

Additional keywords: genetic diversity, rep-PCR fingerprinting.