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The microsatellite data that support the findings of this study are openly available in the CIRAD dataverse at https://dataverse.cirad.fr/dataverse/pvbmt doi:10.18167/DVN1/CI05C6. Minisatellite data are available on the dedicated public database at http://www.biopred.net/mlva.This manuscript is dedicated to his memory of C. Vernière.; International audience; Molecular epidemiology studies are essential to refine our understanding of migrations of phytopathogenic bacteria, the major determining factor in their emergence, and to understand the factors that shape their population structure. Microsatellite and minisatellite typing are useful techniques for deciphering the population structure of Xanthomonas citri pv. citri, the causal agent of Asiatic citrus canker. This paper presents a molecular epidemiology study, which has improved our understanding of the history of the pathogen's introductions into the Arabian Peninsula, since it was first reported in the 1980s. An unexpectedly high genetic diversity of the pathogen was revealed. The four distinct genetic lineages within X. citri pv. citri, which have been reported throughout the world, were identified in the Arabian Peninsula, most likely as the result of multiple introductions. No copper-resistant X. citri pv. citri strains were identified. The pathogen's population structure on Mexican lime (their shared host species) was closely examined in two countries, Saudi Arabia and Yemen. We highlighted the marked prevalence of specialist pathotype A* strains in both countries, which suggests that specialist strains of X. citri pv. citri may perform better than generalist strains when they occur concomitantly in this environment. Subclade 4.2 was the prevailing lineage identified. Several analyses (genetic structure deciphered by discriminant analysis of principal components, R-ST-based genetic differentiation, geographic structure) congruently suggested the role of human activities in the pathogen's spread. We discuss the implications of these results on the management of Asiatic citrus canker in the region.

A thorough knowledge of genotypic and phenotypic variations (e.g., virulence, resistance to antimicrobial compounds) in bacteria causing plant disease outbreaks is key for optimizing disease surveillance and management. Using a comprehensive strain collection, tandem repeat-based genotyping techniques and pathogenicity assays, we characterized the diversity of X. citri pv. citri from the South West Indian Ocean (SWIO) region. Most strains belonged to the prevalent lineage 1 pathotype A that has a wide host range among rutaceous species. We report the first occurrence of genetically unrelated, nonepidemic lineage 4 pathotype A* (strains with a host range restricted to Mexican lime and related species) in Mauritius, Moheli and Réunion. Microsatellite data revealed that strains from the Seychelles were diverse, grouped in three different clusters not detected in the Comoros and the Mascarenes. Pathogenicity data suggested a higher aggressiveness of strains of one of these clusters on citron (Citrus medica). With the noticeable exception of the Comoros, there was no sign of recent interisland movement of the pathogen. Consistent with this finding, the copL gene, a marker for the plasmid-borne copLAB copper resistance that was recently identified in Réunion, was not detected in 568 strains from any islands in the SWIO region apart from Réunion.

High-quality Illumina assemblies were produced from 284 Xanthomonas citri pv. citri pathotype A strains mostly originating from the Southwest Indian Ocean region, a subset of which was also sequenced using MinION technology. Some strains hosted chromosomally encoded transcription activator-like effector (TALE) genes, an atypical feature for this bacterium.

Crop pathogens have been a threat to human kind since the birth of agriculture. However, little is known on the evolutionary processes and ecological factors that underlie their emergence and success, and explain epidemics. Insular ecosystems are especially vulnerable to exotic disease invasions and thus provide a model of particular interest. Nowadays, our understanding of plant pathogens and the diseases they cause greatly benefits from molecular genetics and genomics. In this context, herbarium collections are an enormous source of dated, identified and preserved DNA material that can be used in comparative genomic and phylogeographic studies to elucidate the emergence and evolutionary his-tory of pathogens. In this study, we reconstructed the genomes of 6 historical strains of the Citrus phytopathogen Xanthomonas citri pv. citri ( Xcc) obtained from infected herbarium specimens. We designed a specific extraction protocol suited for bacterial ancient DNA (aDNA) from herbarium spec-imens, and showed the authenticity of our historical samples by assessing DNA damage patterns. We then compared the historical strains to a large set of modern genomes to reconstruct their phylogenetic relationship and estimate several evolutionary parameters at the scale of the Southern Indian Ocean (SIO) islands, using Bayesian tip-calibration inferences. Our results first confirm that Xcc originated in Asia and subsequently spread to the rest of the world, including the SIO islands. We dated the arrival of Xcc in the SIO area to the mid-19th century and hypothesize that it was linked to human migrations following the abolishment of slavery. By analysing the phylogenetic structure of SIO Xcc we suggest that the introduction of the disease happened first in La R´eunion and Mauritius, from which it spread to all other SIO islands. Finally, our results also include the first estimation of a mutation rate for a plant pathogenic bacterium. Our study shows the great potential hidden in herbarium collections to bring light on the evolutionary dynamics that drive pathogens invasion at the scale of the Southern Indian Ocean islands, ultimately helping us to better control current and future crop epidemics.

International audience; Although some plant pathogenic bacteria represent a significant threat to agriculture, the determinants of their ecological success and evolutionary potential are still poorly understood. Refining our understanding of bacterial strain circulation at small spatial scales and the biological significance and evolutionary consequences of co-infections are key questions. The study of bacterial population biology can be challenging, because it requires high-resolution markers that can be genotyped with a high throughput. Here, we overcame this difficulty for Xanthomonas citri pv. citri, a genetically monomorphic bacterium causing Asiatic citrus canker (ACC). Using a genotyping method that did not require cultivating the bacterium or purifying DNA, we deciphered the pathogen's spatial genetic structure at several microgeographic scales, down to single lesion, in a situation of ACC endemicity. In a grove where copper was recurrently applied for ACC management, copper-susceptible and copper-resistant X. citri pv. citri coexisted and the bacterial population structured as three genetic clusters, suggesting a polyclonal contamination. The range of spatial dependency, estimated for the two largest clusters, was four times greater for the cluster predominantly composed of copper-resistant bacteria. Consistently, the evenness value calculated for this cluster was indicative of increased transmission. Linkage disequilibrium was high even at a tree scale, probably due to a combination of clonality and admixture. Approximately 1% of samples exhibited within-lesion multilocus polymorphism, explained at least in part by polyclonal infections. Canker lesions, which are of major biological significance as an inoculum source, may also represent a preferred niche for horizontal gene transfer. This study points out the potential of genotyping data for estimating the range of spatial dependency of plant bacterial pathogens, an important parameter for guiding disease management strategies.

Population biology has the ability to refine our understanding of the biology of plant pathogenic xanthomonads, which remains partial despite the major significance of some of them as agricultural threats. We developed direct microsatellite genotyping from canker lesions caused by Xanthomonas citri pv. citri and applied it to investigate the genetic and spatial structure of the pathogen at several microgeographic scales in a situation of disease endemicity. This approach allowed identifying outbreaks with multiple inoculum sources and comparing genetic lineages in terms of transmission ability. ln a citrus grove where copper-susceptible and copper-resistant strains co-existed, our results suggested a range of spatial dependencyfourtimes largerforthe latter ones. Aggregated spatial patterns estimated from genotyping data were consistent with that previously determined from disease severity data in Argentina. How RST outperformed FST for differentiation analyses was scale-dependent. Linkage disequilibrium was maintained at smalt scales, likely as a confounding consequence of clonality and admixture. Finally, our results highlighted in ca. 1 % of samples a within-lesion polymorphism that likely reflects polyclonal infections. Because of their major biological significance as an inoculum source, we suggest that cankers may represent a preferred niche for horizontal gene transfer.

International audience; Copper-based compounds are widely used in integrated pest management (1PM) programs aiming at controlling agriculturally important plant bacterial pathogens and the latter have adapted in response to this selective pressure. Copper resistance of Xanthomonas citri pv. citri (Xcc), a major citrus pathogen worldwide causing Asiatic citrus canker, was first observed in Argentina two decades ago and subsequently reported as a coplAB-based, plasmid-encoded system. The emergence of resistant strains has since been reported in Réunion (South West lndian Ocean) and Martinique (Eastern Caribbean Sea). Disease severity was found markedly increased in groves established with susceptible cultivars and infected with copper-resistant Xcc. Using tandem repeat-based genotyping and coplAB PCR, we demonstrated that the genetic structure of the copper-resistant strains from these three regions was made up of two distant clusters and varied for the detection of coplAB amplicons. ln order to investigate this pattern more closely, we sequenced six copper-resistant Xcc strains from Argentina, Martinique and Réunion, together with reference copper-resistant Xanthomonas and Stenotrophomonas strains using long-read sequencing technology. Genes involved in copper resistance were found to be straindependent with the novel identification in Xcc of copABCD and a eus heavy metal efflux resistancenodulation- division system. The genes providing the adaptive trait were part of a mobile genetic element similar to Tn3-like transposons and included in a conjugative plasmid. The mining of all bacterial genomes available from public databases suggested that the mobile elements containing copper resistance genes and their plasmid environments were primarily detected in the Xanthomonadaceae family.

Xanthomonas citri pv. citri causes Asiatic citrus canker (ACC), which induces erumpent, callus-like lesions on all aerial organs, and consequently defoliation, premature fruit drop, and twig dieback under high inoculum pressure. Present in most tropical and subtropical citrus producing regions, the disease can lead to important decreases in yield and limitations to export markets due to the quarantine status of the pathogen in some countries ( Graham et al. 2004 ). Strains assigned to genetic lineage 1 within pathotype A, which has the widest host range comprising most citrus cultivars and citrus relatives, were shown to be primarily involved in the worldwide expansion of the bacterium over the 20th century ( Pruvost et al. 2014 ). ACC has been considered endemic in Réunion Island since the 1970s, but was likely present earlier and was not subjected to any eradication attempt. Most citrus growers on the island frequently apply copper-based pesticides as part of integrated pest management programs. A recurring lack of ACC control in several citrus groves was investigated in 2014 using our lab collection of authenticated X. citri pv. citri strains. A total of 501 strains from active epidemics as well as 123 historical strains isolated from 1978 onward were tested for copper resistance using PCR assays targeting copL ( Behlau et al. 2013 ). A total of 115 strains produced the expected amplicon whereas others (including all historical strains) and the negative control (H 2 O) did not. Phenotypic tests were carried out on low-complexing mineral salts casitone-yeast extract-glycerol-agar (CYE) plates ( Zevenhuizen et al. 1979 ) flooded with bacterial suspensions ( ≈ 5 × 10 6 cfu ml –1 ) in sterile tris buffer (pH 7.2), allowed to dry for 15 min., inoculated with a sterile CuSO 4 , 5H 2 O solution (10 mg ml –1 ) with an easySpiral plater used to create a gradient of log-increasing copper concentrations toward the plate center and incubated for 2 days at 28°C. Using this assay, copL + strains grew over a radius (measured from the plate periphery where the concentration of copper are lowest) >23 mm whereas copL – strains growth radius were constantly lower. Copper-resistant strains (CRS) had minimum inhibitory concentrations for copper sulfate ranging from 128 to 256 μ l ml –1 ( Pruvost et al. 1998 ). A subset of 20 CRS and 40 copper-susceptible strains (CSS) (including historical strains) were all assigned to genetic lineage 1 by minisatellite typing (performed as reported by Pruvost et al. 2014 ) and split into two multilocus haplotypes shared also with CSS. CRS were widespread in most citrus production areas of the island where they coexisted with CSS. The oldest CRS dated from 2010. Because no extreme hurricane hit the island between 2010 and 2014, the fast spread of CRS over the island was very likely related to their presence in a major citrus nursery, as confirmed by our data. In Réunion, the European Conformitas Agraria Communitatis (CAC) standards (directive 92/34/EEC) certify the disease-free status of citrus nursery plants (assessed by visual inspections for ACC). CAC is presently recommended but not compulsory. This report suggests that a strict implementation of this procedure would have helped limiting the spread of CRS in Réunion.

Xanthomonas arboricola pv. pruni is the causal agent of the bacterial spot disease of stone fruits, almond and some ornamental Prunus species. In Spain it was first detected in 2002 and since then, several outbreaks have occurred in different regions affecting mainly Japanese plum, peach and almond, both in commercial orchards and nurseries. As the origin of the introduction(s) was unknown, we have assessed the genetic diversity of 239 X. arboricola pv. pruni strains collected from 11 Spanish provinces from 2002 to 2013 and 25 reference strains from international collections. We have developed an optimized multilocus variable number of tandem repeat analysis (MLVA) scheme targeting 18 microsatellites and five minisatellites. A high discriminatory power was achieved since almost 50% of the Spanish strains were distinguishable, confirming the usefulness of this genotyping technique at small spatio-temporal scales. Spanish strains grouped in 18 genetic clusters (conservatively delineated so that each cluster contained haplotype networks linked by up to quadruple-locus variations). Furthermore, pairwise comparisons among populations from different provinces showed a strong genetic differentiation. Our results suggest multiple introductions of this pathogen in Spain and redistribution through contaminated nursery propagative plant material. This work was supported by Instituto Nacional de Tecnología Agraria y Alimentaria. Project RTA-2011-00140-C03-01 (http://www.inia. es) to PLS MCM JP MML, Euphresco project (266505-FP7-ERANET Euphresco II) to PLS MCM JP APB MML, European Social Fund to PLS KB MCM JP APB CV MML OP, European Regional Published

International audience; The Rssc encompasses strains that are highly destructive worldwide causing bacterial wilt (BW) on a wide plant host range. BW was alread y described in Madagascar (phylotype I and III) but potato production was hampered by severe outbreaks. Controlling this disease is crucial for Malagasy potato producers. Knowledge of the genetic diversity and population structure of the pathogen was inves tigated, in fine to evaluate resistance of different potato cultivars. We characterized a large collection of strains (n=1224; 74 sites) surveyed from potato areas in 2013, by using different molecular tools. Phylotypes I, II and III were identified and most potato outbreaks were shown to be associated with brown rot strains IIB - 1, whereas members of phylotype I and III caused few. Along with reference strains, epidemic IIB - 1 strains (n=290) were genotyped through a MLVA scheme ( RS2 - MLVA10), which showed a single clonal complex distributed in wide agro - ecological areas, and genetically related to worldwide genotypes. This suggests this IIB - 1 lineage is busting potato production in Madagascar after being introduced (not cryptic) and spread through release of infected potato - seeds. To assess the population structure of long time recognized phylotype III strains, 251 strains were analyzed through the newly developed and highly discriminatory typing scheme RS3 - MLVA16. Malagasy population of phylotype III strains showed a broad genetic basis made of 132 haplotypes in at least 7 clonal complexes; and furthermore distinct from African strains, suggesting its endemic character. At an agro - ecological scale, two major clonal complexes were unified by haplotypes shared between individual areas and the remainder made of haplotypes derived from a unique genotype. This large - scale epidemiological study and the generated sets of data are reference models to further studies of Rssc population in Madagascar and the SWIO* , including evaluation of pathogen aggressiveness and host resistance. (Résumé d'auteur)

Xanthomonas citri pv. citri, the causal agent of Asiatic citrus canker, is a quarantine pathogen for the European and Mediterranean Protection Plant Organization (EPPO A1 list) and for the European Union (Directive 2000/29/EC annex II A1 – pests absent from the EU). Cases of emergence of this bacterium (Western and Eastern Africa, Australia) correspond to geographical expansion of pathologically - preadapted strains through long distance movement of contaminated plant material. Here we report in Martinique the first outbreak of Asiatic canker in the Caribbean region. The first doubtful lesions were collected mid - 2014 at Morne Rouge from a commercial grove and trees in private gardens when doing surveys targeting huanglongbing, canker and/or other quarantine citrus diseases. A further remote case was identified 12 kilometers away at Le Lorrain in May 2015. Xanthomonas - like cultures were identified and confirmed as X. citri pv. citri on the basis of the EPPO diagnostic protocol PM7/44(1). Strains were further assigned to pathotype A based on pathogenicity tests using a detached leaf assay, MultiLocus Sequence Analysis and MultiLocus Variable number of tandem repeats Analysis targeting 31 minisatellites. The latter technique further assigned outbreak strains to genetic lineage 1, the most widely distributed group of strains. Microsatellite - based genotyping highlighted a very close relatedness between strains f rom the two foci in Martinique. Surprisingly, all strains collected to date in Martinique are copper - resistant even when no extensive copper sprays programs have been used, suggesting that copper - resistant strains were introduced. These initial foci were contained by tree removal and burning and the situation is presently under apparent control. (Texte intégral)

The Ralstonia solanacearum species complex (Rssc) is a highly diverse cluster of strains, many of which proved destructive worldwide causing bacterial wilt (BW) on a wide plant host range. Potato BW has been described for nearly 30 years in Madagascar highlands (phylotype I and Ill) without major impact on production. Recently, potato production was dramatically devastated by severe outbreaks. Controlling this disease is crucial for Malagasy potato producers and a first important step to achieve this goal is the identification of the strains involved and of their putative origin. Consequently, the genetic diversity and population structure of the Rssc was investigated in the major potato production areas in the highlands. By using different molecular tools we characterized a large collection of strains (n=1224; 75 sites) collected from potato production areas in 2013, April (n=763; 41 sites) and December (n=461; 33 sites). Present for a long time in Madagascar, Phylotypes I and Ill strains were little associated with potato BW outbreaks, while surprisingly, most outbreaks were associated with brown rot strains IIB-1. This constitutes the first report of phylotype IIB-1 strains in Madagascar. Along with reference strains, epidemic IIB-1 strains (n=285) were genotyped through the MLVA RS2-MLVA9 implemented from existing schemes (1, 2]. Malagasy phylotype Il strains separated into two clonal complexes (CC) including one major CCl grouping also most of the worldwide genotypes that distributed in wide agro-ecological areas. Fine scale genetic investigation of the outbreak suggested that the clonal expansion of this IIB- lineage affected potato production in Madagascar after being introduced and massively spread through propagation of latently infected potato-seeds. The survey also allowed the first study about the population structure of phylotype Ill strains. Two hundreds and seventeen phylotype Ill strains were genotyped with the highly discriminatory MLVA scheme RS3-MLVA16 that we newly developed [3]. MLVA distinguished a high genetic diversity in Malagasy population of phylotype Ill strains producing 117 haplotypes grouped in 11 clonal complexes. Malagasy strains were distinct from continental African strains, suggesting little recent immigration from the continent. Many CC a long with the large genetic diversity supported the endemic character of the phylotype Ill population in Madagascar. At an agro-ecological scale, phylotype Ill mostly structured in small clonal complexes associated with a single geographic origin each. But two major CCs grouped some haplotypes shared between individuals from different highland areas, and the remainder made of haplotypes derived from a unique origin supporting long distance dispersal most probably through human activities. Although the most popular Malagasy potato cultivars developed by CIP and FIFAMANOR were apparently developing resistance to phylotype Ill strains in the field, we reported no bacterial wilt resistance properties under artificial environment (growth chambers). As expected, the same potato cultivars were highly susceptible to expanding phylotype IIB-1 lineage.

International audience; MultiLocus Variable number of tandem repeat Analysis (MLVA) has been extensively used to examine epidemiological and evolutionary issues on monomorphic human pathogenic bacteria. MLVA is gaining popularity on agriculturally important bacterial plant pathogens as a tool to improve our understanding of their epidemiology. Xanthomonas citri pv. citri, the causal agent of Asiatic citrus canker, is a quarantine organism in several countries and a major threat for the citrus industry worldwide. We screened the genomes of X. citri pv. citri strain IAPAR 306 and of phylogenetically related strains for tandem repeats. Two MLVA schemes targeting minisatellites and microsatellites, respectively, were developed to assess the diversity of this monomorphic bacterium at various spatio-temporal scales. Microsatellites are useful for outbreak investigation. In contrast, minisatellites were used to decipher the global diversity of X. citri pv. citri and revealed four pathotype-specific lineages based on Discriminant Analysis of Principal Components (DAPC). A single lineage (DAPC1) comprised strains that were implicated in the major geographical expansion of X. citri pv. citri during the 20th century. When applied to the analysis of the emergence of in Africa, minisatellites revealed the presence of two different genetic lineages in addition to DAPC1 on this continent, consistent with SNP data derived from draft genome sequences. Using bacterial populations collected in two neighboring Western African countries, Mali and Burkina Faso, we applied these two genotyping schemes to investigate the origin and pathways of these emergences. Minisatellite and SNP data suggested the introduction of two groups of strains in Mali (DAPC1 and DAPC2). DAPC2 was restricted to Bamako district, whereas DAPC1 strains were found much more invasive. The latter strains formed a major clonal complex based on microsatellite data. This suggests that human activities played a major role in the spread of DAPC1 strains via the movement of contaminated propagative material, further supported by the low differentiation between populations from geographically distant nurseries and orchards and the fact that many nursery strains were assigned to the primary or secondary founder haplotypes identified in the minimum spanning tree. Approximate Bayesian Computation analyses supported the hypothesis that strains from Burkina Faso resulted from a bridgehead invasion from Mali. The new minisatellite scheme represents an opportunity for international X. citri pv. citri genotyping and data sharing. The data generated in this study was deposited in the Xanthomonas citri genotyping database (http://www.biopred.net/MLVA/). (Texte intégral)

International audience; Molecular epidemiology studies further our understanding of migrations of phytopathogenic bacteria, the major determining factor in their emergence. Asiatic citrus canker, caused by Xanthomonas citri pv. citri, was recently reported in Mali and Burkina Faso, a region remote from other contaminated areas. To identify the origin and pathways of these emergences, we used two sets of markers, minisatellites and microsatellites, for investigating different evolutionary scales. Minisatellite typing suggested the introduction of two groups of strains in Mali (DAPC 1 and DAPC 2), consistent with microsatellite typing. DAPC 2 was restricted to Bamako district, whereas DAPC 1 strains were found much more invasive. The latter strains formed a major clonal complex based on microsatellite data with the primary and secondary founders detected in commercial citrus nurseries and orchards. This suggests that human activities played a major role in the spread of DAPC 1 strains via the movement of contaminated propagative material, further supported by the frequent lack of differentiation between populations from geographically distant nurseries and orchards. Approximate Bayesian Computation analyses supported the hypothesis that strains from Burkina Faso resulted from a bridgehead invasion from Mali. Multi-locus variable number of tandem repeat analysis and Approximate Bayesian Computation are useful for understanding invasion routes and pathways of monomorphic bacterial pathogens. (Résumé d'auteur)

Xanthomonas citri pv. mangiferaeindicae , causal agent of bacterial canker (or bacterial black spot), is a major pathogen of mango. The bacterium infects leaves, twigs, and fruit on a wide range of mango cultivars with severe defoliation and up to 80% in fruit losses ( Gagnevin and Pruvost 2001 ). Bacterial canker has recently emerged in western Africa. In 2010 it was first reported in Ghana, Burkina Faso, and Mali and subsequently in the Ivory Coast and Benin in 2014 ( Zombré et al. 2015 ). Mango leaves showing typical symptoms of bacterial canker were first observed in August 2015 in five regions of Togo (Savanes, Kara, Centrale, Plateaux, and Maritime). Lesions were black, slightly raised and angular, and sometimes contained a chlorotic halo. Later in the season, fruit symptoms consisted of small water-soaked spots around lenticels that later developed into black, star shaped erumpent lesions. Moreover, twig cankers were also observed sporadically. High disease prevalence was observed in Togo, especially in the three northern provinces (Savanes, Kara, and Centrale). The wide distribution of bacterial canker in Togo suggests that the pathogen may have been present for some years before being identified. Diseased mango leaves were collected for isolation of the agent from all provinces but Maritime. Nonpigmented Xanthomonas -like colonies were readily isolated on KC medium ( Pruvost et al. 2005 ). Multilocus sequence analysis (MLSA) targeting four housekeeping genes ( atpD , dnaK , efp , and gyrB ) ( Bui Thi Ngoc et al. 2010 ) showed 100% sequence identity among 11 Togo strains (LL322 to LL332). These sequences were 100% identical to those of the pathotype strain (CFBP 1716) of X. citri pv. mangiferaeindicae (LL322 GenBank accessions KX171407 to KX171410), but differed from any other assayed X. citri pathovars, including pv. anacardii . Attached leaves of 6-month-old potted mango cv. Maison Rouge from the youngest vegetative flush were infiltrated (10 inoculation sites per leaf for three replicate leaves on three different plants per bacterial strain) with suspensions of eight Togo strains. Bacterial suspensions ( ∼ 1 × 10 5 CFU/ml) were prepared in 10 mM Tris buffer (pH 7.2) from 16-h-old cultures on YPGA ( Ah-You et al. 2007 ). The negative control treatment consisted of three leaves infiltrated with sterile Tris buffer (10 sites per leaf; one leaf per plant). Plants were incubated in a growth chamber at 30 ± 1°C day and 26 ± 1°C night (12-h day/night cycle) at 80 ± 5% relative humidity. All leaves inoculated with the Togo strains produced typical bacterial canker symptoms a week after inoculation. No lesions were recorded from the negative control. X. citri pv. mangiferaeindicae population sizes recovered from leaf lesions 21 days after inoculation ranged from 4 × 10 7 to 8 × 10 8 CFU/lesion, typical of a compatible interaction ( Ah-You et al. 2007 ). Colonies recovered from lesions were identified as the target by atpD sequencing ( Bui Thi Ngoc et al. 2010 ). Koch's postulates have therefore been fulfilled. The wide distribution and high prevalence of the pathogen emphasizes the need for implementing integrated pest management in groves and nurseries.

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