ABSTRACT
Asiatic citrus canker, caused by Xanthomonas citri pv. citri, is a bacterial disease of major economic importance in tropical and subtropical citrus-producing areas. X. citri pv. citri pathotype A can cause severe infection in a wide range of citrus species and induces erumpent, callus-like lesions with water-soaked margins evolving to corky cankers and leading to premature fruit and leaf drop and twig dieback on susceptible/very susceptible cultivars. A chlorotic halo is typically visible around canker lesions on leaves and young fruit, but not on mature fruit and twigs. This quarantine organism can strongly impact both national and international citrus markets. Long distance dispersal is mainly through infected propagative material. Asiatic citrus canker occurs on most islands in the Southwest Indian Ocean region (Comoros, Mauritius, Reunion, Rodrigues, and Seychelles islands), but was not yet reported in Mayotte (EPPO-PQR available at http://www.eppo.int ). In May 2012, typical canker-like symptoms were observed on sweet orange (Citrus sinensis) groves on Mtsamboro islet and soon after on the main island of Mayotte, mostly on sweet oranges, but also on Tahiti limes (C. latifolia) and mandarins (C. reticulata). Eighty-one Xanthomonas-like strains were isolated using KC semi-selective medium (4) from disease samples collected from both commercial groves and nurseries on different Citrus species located all over the island. Sixteen Xanthomonas-like isolates were tentatively identified as X. citri pv. citri based on a specific PCR assay with 4/7 primers (3). All strains but the negative control, sterile water, produced an amplicon of the expected size similar to X. citri pv. citri strain IAPAR 306 used as positive control. Multilocus sequence analysis targeting six housekeeping genes (atpD, dnaK, efp, gltA, gyrB, and lepA) (1,2) fully identified three strains from Mayotte (LJ225-3, LJ228-1, and LJ229-11) as X. citri pv. citri (and not other xanthomonad pathovars pathogenic to citrus or host range-restricted pathotypes of pathovar citri), and more specifically as sequence type ST2 composed of pathotype A strains of X. citri pv. citri (2) (including all strains from the Southwest Indian Ocean region). Eight strains were inoculated by a detached leaf assay (2) to Mexican lime SRA 140 (C. aurantifolia), Tahiti lime SRA 58, sweet orange cv. Washington Navel, alemow SRA 779 (C. macrophylla), and tangor cv. Ortanique (C. reticulata × C. sinensis) and developed typical erumpent, callus-like tissue at wound sites for all Citrus species, fulfilling Koch's postulates. Xanthomonas-like yellow colonies were reisolated from symptoms produced by the eight strains inoculated on Mexican lime. Boiled bacterial suspensions were assayed by PCR with 4/7 primers (3) and produced the expected 468-bp amplicon in contrast with the negative control (sterile water). No lesions developed on the negative control consisting of inoculations by 10 mM tris buffer (pH 7.2). Citrus canker-free nurseries and grove sanitation should be implemented for decreasing the prevalence of Asiatic canker in this island territory. References: (1) N. F. Almeida et al. Phytopathology 100:208, 2010. (2) L. Bui Thi Ngoc et al. Int. J. Syst. Evol. Microbiol. 60:515, 2010. (3) J. S. Hartung et al. Phytopathology 86:95, 1996. (4) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005.
ABSTRACT
In June 2003, symptoms of stunting and leaf curling resembling symptoms of tomato leaf curl disease, as well as reductions in yields, were observed on tomato plants in the western (Combani and Kahani) and eastern (Dembeni, Kaoueni, and Tsararano) regions of Mayotte, a French island in the Comoros Archipelago located in the northern part of the Mozambique Channel. The whitefly, Bemisia tabaci (Gennadius), was observed colonizing tomato plants and other vegetable crops at low levels. Overall, 13 leaf samples with symptoms were collected from tomato plants among the five regions and tested for the presence of begomoviruses using a polymerase chain reaction (PCR) assay with two sets of degenerate primers designed to amplify two regions of the A component of begomoviruses. Primers MP16 and MP82 amplify an approximately 500-bp fragment located between the intergenic conserved nonanucleotide sequence and the first 200 bp of the coat protein (CP) gene (2). Primers AV494 and AC1048 amplify the approximately 550-bp core region of the CP gene (3). Six leaf samples, one from Combani, three from Dembeni, and two from Kahani, gave a PCR product of the expected size with both sets of primers. No PCR products were obtained with degenerate primers designed for begomovirus DNA B or ß. The approximately 500- and 550-bp PCR products from one sample each of Combani (EMBL Accession Nos. AJ620912 and AJ620915, respectively), Dembeni (EMBL Accession Nos. AJ620911 and AJ620914, respectively), and Kahani (EMBL Accession Nos. AJ620913 and AJ620916, respectively) were sequenced. For the 489-bp sequences obtained with the MP16/MP82 primer set, the three isolates had 90 to 95% nucleotide identity (DNAMAN; Lynnon BioSoft, Quebec). The most significant sequence alignments (NCBI and BLAST) were with begomoviruses; 80 to 83% nucleotide identity was obtained with the Tomato yellow leaf curl Morondava virus (TYLCMV) isolates from Madagascar (EMBL Accession Nos. AJ422123 and AJ422124), 80 to 82% nucleotide identity was obtained with the South African cassava mosaic virus (SACMV) isolates (GenBank and EMBL Accession Nos. AF155806 and AJ422132), and 79 to 81% nucleotide identity was obtained with the East African cassava mosaic Malawi virus (EMBL Accession No. AJ006460). For the 522-bp sequences obtained with the AV494/AC1048 primer set, 95 to 97% nucleotide identity was shown between the three isolates. The most significant sequence alignments were also with begomoviruses; TYLCMV isolate Morondava (EMBL Accession No. AJ422125) with 86 to 88% nucleotide identity, Tomato yellow leaf curl virus isolates (GenBank and EMBL Accession Nos. AF105975, AJ489258, AB014346, AF024715, AF071228, and X76319) with 86 to 87% nucleotide identity, and SACMV isolate M12 (EMBL Accession No. AJ422132) with 85 to 86% nucleotide identity. According to the current taxonomic criteria for the provisional classification of a new begomovirus species, nucleotide sequence identity in the core region of the CP <90% (1), the tomato begomovirus from Mayotte is a new species and is provisionally named Tomato leaf curl Mayotte virus. References: (1) J. K. Brown et al. Arch. Virol. 146:1581, 2001. (2) P. Umaharan et al. Phytopathology 88:1262, 1998. (3) S. D. Wyatt and J. K. Brown. Phytopathology 86:1288, 1996.
