Bacterial spot of tomato and pepper, a major problem in tropical climates, can be caused by several Xanthomonas genospecies. We examined the genetic and pathological diversity of a collection of 72 strains from the southwest Indian Ocean region as part of a regional research and development program to update inventories of agricultural pests and pathogens. Xanthomonas euvesicatoria, X. perforans, X. gardneri, and X. vesicatoria were identified in our strain collection. The identification of strains at the species level was consistently achieved by amplified fragment length polymorphism (AFLP) and multilocus sequence analysis (MLSA). Overall, X. euvesicatoria was the species recovered prevalently. MLSA data based on four housekeeping genes identified two to three sequence types per genospecies. It suggested that sequence variations primarily consisted of synonymous mutations, although a recombination event spanning several hundred nucleotides was detected for some strains of X. euvesicatoria on the atpD gene coding for the F1-F0-ATPase β subunit. The pathogenicity of strains was consistent with data found in the literature. Some pathological variations were primarily observed among strains identified as X. euvesicatoria. This study provides the first ever comprehensive description of the status of Xanthomonas species that cause bacterial spot of tomato and pepper in the southwest Indian Ocean region.

Epidemiological surveillance of plant pathogens based on genotyping methods is mandatory to improve disease management strategies. In the Southwest Indian Ocean (SWIO) islands, bacterial wilt (BW) caused by the Ralstonia solanacearum species complex (RSSC) is hampering the production of many sustainable and cash crops. To thoroughly analyze the genetic diversity of the RSSC in the SWIO, we performed a wide sampling survey (in Comoros, Mauritius, Reunion, Rodrigues, and Seychelles) that yielded 1,704 isolates from 129 plots, mainly from solanaceous crops. Classification of the isolates to the four major RSSC phylogenetic groups, named phylotypes, showed that 87% were phylotype I, representing the most prevalent strain in each of the SWIO islands. Additionally, 9.7% were phylotype II, and 3.3% were phylotype III; however, these isolates were found only in Reunion. Phylotype IV (2 isolates), known to be restricted to Indonesia-Australia-Japan, was reported in Mauritius, representing the first report of this group in the SWIO. Partial endoglucanase (egl) sequencing, based on the selection of 145 isolates covering the geographic and host diversity in the SWIO (also including strains from Mayotte and Madagascar), revealed 14 sequevars with Reunion and Mauritius displaying the highest sequevar diversity. Through a multilocus sequence analysis (MLSA) scheme based on the partial sequencing of 6 housekeeping genes (gdhA, gyrB, rplB, leuS, adk, and mutS) and 1 virulence-associated gene (egl), we inferred the phylogenetic relationships between these 145 SWIO isolates and 90 worldwide RSSC reference strains. Phylotype I was the most recombinogenic, although recombination events were detected among all phylotypes. A multilocus sequence typing (MLST) scheme identified 29 sequence types (STs) with variable geographic distributions in the SWIO. The outstanding epidemiologic feature was STI-13 (sequevar I-31), which was overrepresented in the SWIO and obviously reflected a lineage strongly adapted to the SWIO environment. A goeBURST analysis identified eight clonal complexes (CCs) including SWIO isolates, four CCs being geographically restricted to the SWIO, and four CCs being widespread beyond the SWIO. This work, which highlights notable genetic links between African and SWIO strains, provides a basis for the epidemiological surveillance of RSSC and will contribute to BW management in the SWIO.

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Bacterial spot of tomato and pepper (BSTP) can be caused by several Xanthomonas genospecies (2). BSTP is a major disease in Grenada where A and B phenotypic groups (Xanthomonas euvesicatoria and X. vesicatoria, respectively, [2]) have been reported (3). There is no previous report of group A strains, which are strongly amylolytic and pectolytic, in Grenada. In March 2007, tomato and pepper leaves with lesions typical of BSTP were collected in Saint David and Saint Andrew parishes of Grenada. Bacterial isolations were performed on KC semiselective agar medium (4), resulting in isolation of five yellow-pigmented, Xanthomonas-like strains. Three strains isolated from tomato or pepper in Saint David were negative for starch hydrolysis and pectate degradation, two tests that were found useful for strain identification in the 1990s (2). Two strains isolated from pepper in Saint David were strongly amylolytic and degraded pectate. Amplified fragment length polymorphism (AFLP) and multilocus sequence analysis (MLSA) assays targeting atpD, dnaK, efp, and gyrB were performed on the five strains from Grenada together with a type strain of each of X. euvesicatoria, X. perforans, X. gardneri, and X. vesicatoria as well as other reference strains of X. euvesicatoria and X. perforans as described previously (1). All strains from Grenada were identified as X. euvesicatoria regardless of the typing technique. On the basis of AFLP assays, the two strains with phenotypic features not reported in Grenada were closely related (distances of ≤0.002 nucleotide substitutions per site [1]) to a group of strains from India (ICMP 3381, LMG 907, LMG 908, and LMG 918). These two strains were also identical to the Indian strains based on MLSA, but differed from the X. euvesicatoria type strain by at least one nucleotide substitution in all loci examined. The three strains from Grenada that were negative for starch hydrolysis and pectate degradation had sequences identical to that of the type strain. Young leaves of tomato plants of cv. Marmande and pepper plants of cvs. Yolo Wonder and Aiguille were infiltrated (six inoculation sites per leaf, three replicate plants per cultivar per experiment, and the experiment was replicated once) using inoculum of each of the five strains from Grenada made from suspensions in Tris buffer containing approximately 1 × 105 CFU/ml. Two reference strains of X. euvesicatoria (NCPPB 2968 and LMG 922) were also inoculated as positive control treatments. Negative control treatments consisted of leaves infiltrated with sterile Tris buffer. Typical water-soaked lesions that developed into necrotic spots were observed 3 to 8 days after inoculation (dai) for all strains on all cultivars, except NCPPB 2968, which was not pathogenic on pepper cv. Aiguille. Xanthomonas population sizes from lesions plated onto KC agar medium (4) 25 dai ranged from 3 × 106 to 5 × 107, 8 × 107 to 2 × 108, and 9 × 106 to 2 × 108 CFU/lesion on tomato cv. Marmande and pepper cvs. Yolo Wonder and Aiguille, respectively. The epidemiological importance of this previously unreported group of X. euvesicatoria strains in Grenada needs to be assessed. References: (1) L. Bui Thi Ngoc et al. Int. J. Syst. Evol. Microbiol. 60:515, 2010. (2) J. B. Jones et al. Syst. Appl. Microbiol. 27:755, 2004. (3) L. W. O'Garro. Plant Dis. 82:864, 1998. (4) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005.