Identification of a highly virulent strain of <Emphasis Type="Italic">Xanthomonas axonopodis</Emphasis> pv. <Emphasis Type="Italic">malvacearum</Emphasis>

A highly virulent strain (HVS) of Xanthomonas axonopodis pv. malvacearum (Xam) was first reported in Africa in 1983, infecting all commercial cultivars of cotton including the immune cv. ‘101–102B’. The HVS was considered to be a new race of pathovar malvacearum (race 20). Here we studied a HVS (GSPB 2388) isolated in Sudan, which causes symptoms that clearly differed from the typical angular water-soaked spots of bacterial bright of cotton. Our investigations showed that extracellular cellulase activity of this HVS was higher than that of the control strain GSPB 1386 (race 18). Additionally, SDS-PAGE indicated that the HVS cell wall contained short LPS molecules with fewer O-chain repeating units, lacking in GSPB 1386. The higher cellulase activity and the distinct lipopolysaccharide of HVS are correlated with the higher virulence and deviating symptom formation. Rep-PCR fingerprinting showed that the HVS was very closely related to other strains of Xam.     

Detection of <Emphasis Type="Italic">Xanthomonas axonopodis</Emphasis> pv. <Emphasis Type="Italic">manihotis</Emphasis>, the causal agent of cassava bacterial blight diseases in cassava (<Emphasis Type="Italic">Manihot esculenta</Emphasis>) in Ghana by polymerase chain reaction

Xanthomonas axonopodis pv. manihotis (Xam) is the causal agent of cassava bacterial blight (CBB) disease. CBB is a major constraint to cassava cultivation in Ghana. In this study, a survey was conducted in eight regions of Ghana to assess the presence of CBB disease. Out of the eight regions visited, CBB, though at different prevalence, was observed in five regions. Cassava plants samples showing suspected bacterial blight symptoms were collected for analysis by Polymerase Chain Reaction (PCR). The results of the analysis showed that Ashanti region had the highest prevalence in percentage of CBB, which recorded (70%), followed by Volta region (60%); Brong Ahafo region (40%); Eastern region (40%) and Greater Accra region (20%). Morphological examination of the putative pathogen was carried out on Cefazolin trehalose agar (CTA) and Nutrient agar (NA) media. The isolates were subjected to conventional PCR using Xanthomonas genus specific primer, RST2/RST3, Xam specific Variable Number Tandem Repeat (VNTRs) loci, XaG1_67F/R and X-gumD primers, which produced 840, 446 and 402 bp, respectively. The isolates also tested positive with SYBR Green fluorescent dye, using Real-time PCR. The resulting PCR products were sequenced and analyzed using a BLASTn program, which revealed homology between 93 and 100% with several other Xam strains retrieved from GenBank nucleotide database. The pathogenicity test of the isolates on the susceptible Esam cassava variety produced symptoms typical of Xam and the pathogen was consistently re-isolated from the inoculated cassava plants and thereby satisfying the Koch’s postulates.     

Evaluation of seedborne bacterial pathogens on common bean cultivars grown in central Anatolia region,Turkey

Bacterial diseases of bean cause economically important losses worldwide. The most important method for managing bacterial diseases on bean is the use of pathogen-free seed. In this study, 198 different dry bean seed samples of six different cultivars including Dermason, Cali, Sira, Battal, Bombay and Seker, were collected from 12 provinces of Central Anatolia Region of Turkey. All were tested to investigate the seedlots as primary inoculum sources of the major bacterial diseases. The data revealed that 22,72 %, 13,63 %, 11,11 %, 1,51 % and 0.5 % of seed samples tested were contaminated with five seedborne bacterial pathogens, Pseudomonas savastanoi pv. phaseolicola (Psp), Pseudomonas syringae pv. syringae (Pss), Xanthomonas axonopodis pv. phaseoli (Xap), X. axonopodis pv. phaseoli var. fuscans (Xapf) and Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), respectively. All bacterial strains isolated were identified based on morphological, physiological, biochemical, molecular and pathogenicity tests. The results showed that Psp and Pss were found together on cv. Cali; Psp and Xap on cv. Dermason and cv. Sira; and Pss and Xap on cv. Seker, cv. Dermason, and cv. Cali. Therefore, the results in the present study suggested that evaluation and selection of pathogen-free seeds are very important for preventing the spread of pathogens and effective management of seed borne bacterial diseases prevalent in bean growing regions; in addition to implementation of integrated crop production strategies such as crop rotation, sanitation, seed treatment, tolerant/resistant cultivar selection and proper bactericide application.     

Consequences of the taxonomic revision of Xanthomonas axonopodis pv. dieffenbachiae and of the analysis of its associated pathogenicity for the recommendation of regulation (EPPO A2 List)

Xanthomonas axonopodis pv. dieffenbachiae, the causal agent of bacterial blight of Araceae (aroids), is a regulated pest in several countries and is included in the EPPO A2 List. Reference strains of Xanthomonas axonopodis pv. dieffenbachiae have recently been reclassified into the species Xanthomonas phaseoli, Xanthomonas citri and Xanthomonas euvesicatoria on the basis of different features, including multilocus sequence analysis, average nucleotide identity and homology in DNA–DNA hybridization analyses. Based on pathogenicity tests, Constantin et al. (2017) proposed naming the pathogens on aroids as X. phaseoli pv. dieffenbachiae, X. phaseoli pv. syngonii and X. citri pv. aracearum. Recommendations are made on how to deal with these changes for the group of pathogenic bacteria for Araceae. The name Xanthomonas axonopodis pv. dieffenbachiae on the EPPO List should be adjusted to the names proposed in the taxonomic study by Constantin et al. (2016). The current EPPO Diagnostic Standard is directed at strains pathogenic on Anthurium. They mainly belong to X. phaseoli pv. dieffenbachiae, but some also to X. citri pv. aracearum that are not detected by the EPPO Diagnostic Standard. Xanthomonas phaseoli pv. syngonii strains are also aggressive, but with a host range restricted to Syngonium. The pathogenicity specific to aroids of the bacterial isolates reclassified as Xanthomonas euvesicatoria was not confirmed and no pathovar epithet has been retained for these strains.     

Critical disease components of common bacterial blight to effectively evaluate resistant genotypes of snap bean

Common bacterial blight (CBB) caused by Xanthomonas axonopodis pv. phaseoli (Xap) is the main bacterial disease of snap bean. The present work aimed to select snap bean genotypes that are resistant to CBB based on three components of resistance: area under the disease progress curve, latent period, and lesion diameter on pods (DL). A completely randomized two-factor factorial design with six replications was used to evaluate leaves and pods of 14 snap bean and three common bean genotypes (PI 207262, BAC-6 and A-794) with high resistance to CBB. Two Xap isolates, 1394-98 and 775-90, were used to inoculate leaves and pods. Data were analyzed using nonparametric statistics. Significant differences were observed among the evaluated genotypes for all of the components of resistance, except for DL. The snap bean UENF 1482 demonstrated good performance in two disease resistance components. For this reason, this genotype can be recommended for use in breeding programs that aim to generate snap bean genotypes resistant to Xanthomonas axonopodis pv. phaseoli.     

Structural conservation of the <Emphasis Type="Italic">hrp</Emphasis> gene cluster in <Emphasis Type="Italic">Xanthomons oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis>

The clustered hrp genes encoding the type III secretion system in the Japanese strains MAFF301237 and MAFF311018 of Xanthomonas oryzae pv. oryzae were sequenced and compared. The strains differ in their pathogenicity, location, and year of isolation. A 30-kbp sequence comprising 29 open reading frames (ORFs) was identical in its structural arrangement in both strains but differed from X. campestris pv. campestris, X. axonopodis pv. citri, and X. axonopodis pv. glycines in certain genes located between the hpaB-hrpF interspace region. The DNA sequence and the putative amino acid sequence in each ORF was also identical in both X. oryzae pv. oryzae strains as were the PIP boxes and the relative sequences. These facts clearly showed that the structure of the hrp gene cluster in X. oryzae pv. oryzae is unique.     

Characterisation of Xanthomonas campestris pv. campestris isolates from South Africa using genomic DNA fingerprinting and pathogenicity tests

The genetic diversity of Xanthomonas campestris pv. campestris isolates from South Africa was evaluated using 28 isolates obtained from the Johannesburg Fresh Produce Market. Samples were collected from cabbage supplies from farms in Gauteng, Mpumalanga and North West Provinces. Strains were isolated from small sections of infected cabbage leaf samples and cultured on Yeast Dextrose Agar. Isolates identity was confirmed by ELISA and Pathogenicity test. Pathogenicity tests were performed by inoculating leaves of known susceptible cabbage seedlings. Infection symptoms induced could be categorized into three groups, ranging from typical to non-typical black rot symptoms. Four differential Brassica cultivars with known avirulence genes were used for race typing done by spray inoculation. Four races, namely 1, 3, 4 and 6, were identified. Of the 28 isolates, four were identified as race 1, two as race 3, 19 as race 4 and three as race 6. Repetitive DNA polymerase chain reaction-based fingerprinting using Eric- and Box-primers was used to assess the genetic diversity. Generated fingerprints of X. c pv. campestris were relatively similar. Cluster analysis could not strictly group isolates by their geographical origin, suggesting limited diversity of Xanthomonas campestris pv. campestris strains within cabbage producing regions in South Africa.     

Identification of new resistant sources for bacterial blight in pomegranate

Bacterial blight is a highly devastating disease caused by Xanthomonas axonopodis pv. punicae, recording 60 to 80 percent yield-loss of pomegranate in India. In the present investigation, a total of 209 genotypes including 105 exotic types from USDA, 66 wild types and 38 cultivated types from India were screened and categorized into fifteen clusters using cluster and principal component analysis. Genotypes of cluster 15, viz. 108 B and 99 A from USDA and 318734, Daru-18 and IIHR-30 from India, were found to be resistant to bacterial blight while genotypes of cluster 9 were highly susceptible. Two genotypes, each from cluster 15 (318734) and 9 (Ruby), were compared for biochemical and histological parameters to understand the defense mechanism. Significantly, higher accumulation of defense related metabolites, viz. total phenol, flavonoid and antioxidant contents, were observed in resistant genotype (318734). Fewer numbers of stomatal pores that served as portals of entry for plant pathogens were recorded in this genotype. Resistance observed in genotype 318734 might be due to an incompatible interaction between host and pathogen compared to other genotypes. This is the first report of putative resistance sources in pomegranate against Xanthomonas axonopodis pv. punicae.     

Characterization of <Emphasis Type="Italic">Myoviridae</Emphasis> and <Emphasis Type="Italic">Podoviridae</Emphasis> family bacteriophages of <Emphasis Type="Italic">Erwinia amylovora</Emphasis> from Hungary - potential of application in biological control of fire blight

The virulence spectrum of 300 isolates of Xanthomonas oryzae pv. oryzae (Xoo), representing 17 districts of Punjab, Pakistan was elucidated through inoculation on a set of six rice IRRI-differentials. The virulence level was assessed by using principal component and cluster analysis. Among six principal components (PCs), PC-1 exhibited 59.3 % of the total variance. The highly virulent isolates clusters on the positive side of the ordination away from the point of intersection of PC1 and PC2 and classifies the Xoo isolates from slow disease to the highest disease causing entities. The 300 isolates were categorized into 29 pathotypes (Pt1-29) wherein the highly virulent pathotype (Pt-1), comprises of 39 Xoo isolates were widespread in 12 districts. The majority of Xoo isolates were moderately to least virulent (21.7–43 %) and average disease progress curves confirmed the field reactions of these pathotype clusters for an efficient recognition of Xoo isolates. Interaction of the pathogen with differentials harboring different resistant genes was well investigated in the current study for future management approaches for which the surveillance of the new Xoo pathotypes may expedite the disease resistant rice breeding programme in the country.     

Virulence profiling of <Emphasis Type="Italic">Xanthomonas oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis> isolates,causing bacterial blight of rice in India

Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo), remains a major production constraint in rice cultivation especially in irrigated and rainfed lowland ecosystems in India. The pathogen is highly dynamic in nature and knowledge on pathotype composition among the Xoo population is imperative for designing a scientific resistance breeding program. In this study, four hundred isolates of Xoo collected from diverse rice growing regions of India were analyzed for their virulence and genetic composition. Virulence profiling was carried out on a set of differentials consisting of 22 near isogenic lines (NILs) of IR24 possessing different BB resistance genes and their combinations along with the checks. It was observed that different NILs possessing single BB resistance gene were susceptible to about 59–94% of the Xoo isolates except IRBB 13 (containing BB resistance gene xa13), which showed susceptibility to about 35% of the isolates. Based on the reaction of the Xoo isolates on the differentials, they were categorized into 22 pathotypes. Among the 22 pathotypes, IXoPt-1 and IXoPt-2 were least virulent and IXoPt # 18–22 were highly virulent. Pathotype IXoPt-19 which was virulent on all single BB resistance genes except xa13 constituted the major pathotype (22.5% isolates) and was widely distributed throughout India (16 states). This was followed by pathotype IXoPt-22 (17.25%) which was virulent on all the NILs possessing single BB resistance genes. Molecular analysis was carried out using two outwardly directed primers complementary to sequence of IS1112, a repetitive element of Xoo. A high level of genetic polymorphism was detected among these isolates and the isolates were grouped into 12 major clusters. The data indicated complex nature of evolution of the Xoo pathotypes and there was no strong correlation between pathotypes and genetic clusters as each genetic cluster was composed of Xoo isolates belonging to different pathotypes. The study indicated that none of the single BB resistance genes can provide broad spectrum resistance in India. However, two-gene combinations like xa5 + xa13 and different 3 or 4 genes combination like Xa4 + xa5 + xa13, Xa4 + xa13 + Xa21, xa5 + xa13 + Xa21 and Xa4 + xa5 + xa13 + Xa21 are broadly effective throughout India.     

A diagnostic medium for the semi-selective isolation and enumeration of <Emphasis Type="Italic">Xanthomonas axonopodis</Emphasis>pv. <Emphasis Type="Italic">vignicola</Emphasis>

A semi-selective medium for isolation of Xanthomonas axonopodis pv. vignicola from cowpea (Vigna unguiculata) plant and soil samples was developed. Twelve carbon and five nitrogen sources were tested with four strains of X. axonopodispv.vignicola, and 25 antibiotics were screened against saprophytes. -cellobiose (10g) was selected as the optimal carbon source. Among the antibiotics, cefazoline inhibited growth of most of the saprophytes with little effect on strains of the pathogen. ,-methionine enhanced growth of X. axonopodispv.vignicola. Boric acid along with ammonium chloride suppressed growth of Pseudomonas fluorescens. The semi-selective medium designated as cefazoline-cellobiose-methionine (CCM) medium contained K₂HPO₄ 1.34g, KH₂PO₄ 0.4g, MgSO₄ 0.3g, H₃BO₃ 0.2g, NH₄Cl 1.0g, -cellobiose 10g, cycloheximide 0.2g, ,-methionine 1.0g, cefazoline 10mg and agar 14g per l of water (pH 7.2). Colonies of X. axonopodispv.vignicola on CCM medium were whitish, round, raised and 0.2–1.8mm in diameter 96h after incubation. CCM medium generally inhibited growth of Pantoea agglomerans, Bacillus subtilis and saprophytes isolated from cowpea leaves. Colonies of Pseudomonas fluorescens and a saprophytic bacterium, which were not completely suppressed by CCM, could be differentiated from X. axonopodispv.vignicola by their smaller size and different color. The CCM medium proved useful for isolation of X. axonopodispv.vignicola from cowpea plant and soil samples. This is the first report of a semi-selective medium developed for detection of X. axonopodispv.vignicola.     

Evaluation of glyphosate-tolerant soybean cultivars for resistance to bacterial pustule

Xanthomonas axonopodis pv. glycines causes bacterial pustule of soybean, which is a common disease in many soybean-growing areas of the world and is controlled by a single recessive gene (rxp gene) commonly found in many conventional glyphosate-sensitive soybean cultivars. Since glyphosate-tolerant cultivars are commonly planted today, there has been no information about whether these new cultivars have bacterial pustule resistance. The goal of this study was to screen glyphosate-tolerant soybean cultivars for resistance to X. axonopodis pv. glycines. Three experiments were completed to evaluate resistance. In experiment 1, 525 commercial glyphosate-tolerant cultivars from 2001 were inoculated with X. axonopodis pv. glycines strain UIUC-1. Following inoculation, many of the cultivars were resistant (developed no detectable pustule symptoms) although 152 (~29%) developed bacterial pustule. In experiment 2, the aggressiveness of three strains (UIUC-1, UIUC-2, and ATCC 17915) of X. axonopodis pv. glycines were compared on three bacterial pustule-susceptible, glyphosate-tolerant cultivars. One strain (UIUC-1) was less aggressive than the other two (UIUC-2 and ATCC 17915) on all three cultivars examined. In experiment 3, 45 cultivars from 2005 (all different from 2001) were inoculated with X. axonopodis pv. glycines ATCC 17915. A range of disease severities developed with five cultivars (11%) having disease severity ratings as high as or higher than those on a susceptible check cultivar. Overall, these results suggested that resistance to bacterial pustule occurs in glyphosate-tolerant soybean cultivars, but not at 100% frequency, which means bacterial pustule outbreaks could occur when a susceptible cultivar is planted and conditions are conducive for bacterial pustule development.     

Genetic fingerprinting of Iranian Xanthomonas campestris pv. campestris strains inducing black rot disease of crucifers

Northern Iran has one of the largest and most diverse populations of cultivated crucifers in Iran. Symptoms of black rot disease were observed in 40 % of fields. To assess the genetic diversity of Xanthomonas campestris pv. campestris (Xcc) strains, associated with black rot disease, 40 strains were isolated from infected samples of crucifers such as cabbage, radish, cauliflower, turnip and kohlrabi, and were collected from different geographic regions of northern Iran including West and East Azarbayjan and Ardabil provinces. Bacterial strains were characterized by their morphological, biochemical and physiological features and pathogenicity tests. Four races were found in northern Iran (1, 4, 5 and 6) and the majority of the tested strains belonged to either race 4 (45 %) or race 6 (20 %). To examine the distribution of dispersed repetitive DNA, Enterobacterial Repetitive Intergenic Consensus (ERIC), BOX, Repetitive Extragenic Palindromic (REP) and random amplified polymorphic DNA (RAPD) sequences in the genome of Xcc using conserved primers. The different markers produced characteristic banding patterns and the similarity matrices from binary banding data was derived with the similarity for qualitative data program (SIMQUAL). On the basis of the fingerprint patterns generated by the combination data set of both rep-PCR and RAPD, the Xcc strains were differentiated into seven clusters (A–G) at 76 % similarity level. The geographical origin of the Iranian strains does not seem to be correlated with the RAPD and rep-PCR clusters. The clusters seem to be more related to the race of the strains. This is the first study on genetic diversity of Xcc strains inducing black rot disease of crucifers in Iran.     

Bacterial leaf spot of hemp caused by Xanthomonas campestris pv. cannabis in Japan

Bacterial leaf spot disease of hemp was observed in Tochigi Prefecture, Japan in 1982 and characterized by necrotic lesions ca. 1–2 mm diameter on leaves with a yellow halo 2–3 mm wide. In this report, we describe the pathological, physiological and genetic properties of the causal bacterium. Our results indicated that this bacterium is identical with Xanthomonas campestris pv. cannabis reported in Romania.     

Leaf blight and defoliation caused by two new pathovars of Xanthomonas axonopodis on Schinus terebinthifolius and Mabea fistulifera

Schinus terebinthifolius and Mabea fistulifera have been used for forest repositioning and urban forestry in Brazil. In October 2012, in a routine inspection at the research nursery of the Forestry Department of the Universidade Federal de Viçosa, in Minas Gerais, Brazil, a mortality of approximately 40% of the seedlings was observed as a result of diseases characterized by leaf blight and intense defoliation, which culminated in the death of the plants. Microscopy observations revealed oozing from the infected tissue and isolations revealed a bacterial aetiology for both diseases. Bacterial cells that formed bright yellow mucoid colonies with round edges were routinely isolated from lesion margins. Inoculation of isolated strains into healthy seedlings reproduced the symptoms observed under natural conditions. Bacterial cells showing the same morphological, biochemical and molecular characteristics as those originally isolated from naturally infected plants were reisolated from inoculated plants. Morphological, physiological and biochemical tests as well as 16S rDNA sequencing and multilocus sequence analysis using four housekeeping genes, dnaK, fyuA, gyrB and rpoD, confirmed the newly isolated strains belong to Xanthomonas axonopodis. Plant cross‐inoculations showed the strains did not belong to any known phylogenetically related pathovar. Pathovars X. axonopodis pv. schini pv. nov. and X. axonopodis pv. mabeae pv. nov. are proposed as the causal agents of bacterial leaf blight on S. terebinthifolius and M. fistulifera, respectively.     

PM 7/128 (1) Xanthomonas axonopodis pv. allii

Specific scope

This Standard describes a diagnostic protocol for Xanthomonas axonopodis pv. allii. 1 This Standard should be used in conjunction with PM 7/76 Use of EPPO diagnostic protocols.

Specific approval and amendment

First approved in 2016‐09.     

Regulatory network of hrp gene expression in Xanthomonas oryzae pv. oryzae

Like other plant-pathogenic bacteria, Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight of rice, has hrp genes that are indispensable for its virulence. The hrp genes are involved in the construction of the type III secretion (T3S) apparatus, through which dozens of virulence-related proteins, called effectors, are directly secreted into plant cells to suppress and disturb plant immune systems and/or induce plant susceptibility genes. The expression of hrp genes is strictly regulated and induced only in plants and in certain nutrient-poor media. Two proteins, HrpG and HrpX, are known as key regulators for hrp gene expression. Great efforts by many researchers have revealed unexpectedly that, besides HrpG and HrpX, many regulators are involved in this regulation, some of which also regulate the expression of virulence-related genes other than hrp. Moreover, it has been found that HrpG and HrpX regulate not only hrp genes and effector genes but also genes unrelated to the T3S system. These findings suggest that the expression of the hrp gene is orchestrally regulated with other virulence-related genes by a complicated, sophisticated regulatory network in X. oryzae pv. oryzae.     

Characterization of a unique copper resistance gene cluster in <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis> isolated in Trinidad,West Indies

Whole genome sequencing of a copper resistant (Cu^R) black rot strain of Xanthomonas campestris pv. campestris (Xcc) isolated from a broccoli plant in Trinidad revealed a unique operon for copper resistance. The cop genes of strain Xcc-BrA1 were determined to be present on a 160 to 180 kb plasmid shown to be non-conjugative with other xanthomonads. While nucleotide comparison of a putative 8.0 Kbp copLABMGF gene cluster identified in Xcc-BrA1 genome did not reveal any homologous region with other known Cu^R Xanthomonas strains from diverse origins, the comparison of the translated amino acid sequence indicated similarity with X. citri, X. c. pv. citrumelonis and X. vesicatoria Cop proteins. Cloning of the copLAB gene cluster from Xcc-BrA1 conferred copper resistance to other copper-sensitive xanthomonads. Although Xcc-BrA1 harbors copLAB genes with similar sizes and organization and is able to grow on Cu-amended medium as other Cu^R xanthomonads, the phylogenetic analysis of nucleotide sequences indicates that the cop cluster in Xcc-BrA1 is unique and distantly related to other copLAB genes from Xanthomonas and Stenotrophomonas. The origin of copper resistance genes in Xcc-BrA1 is likely a result of horizontal gene acquisition from a still unknown phylloplane cohabitant. The findings of this study have implications for the management of crop diseases caused by Cu^R xanthomonads. Future studies could focus on and determining the distribution, overall importance and appropriate control measures for strains harbouring these unique genes.     

Sensitive detection of Xanthomonas axonopodis pv. dieffenbachiae on Anthurium andreanum by immunocapture-PCR (IC-PCR) using primers designed from sequence characterized amplified regions (SCAR) of the blight pathogen

One of the most devastating Xanthomonas diseases affecting the Anthurium cut flower industry worldwide is the bacterial blight caused by Xanthomonas axonopodis pv. dieffenbachiae (Xad). The disease can be spread through latently infected tissue-cultured plants that are used for the propagation of Anthurium worldwide. Current disease diagnostic techniques involve the use of semi-selective media and serological tests. This study describes the development of a PCR tool combined with a genus-specific monoclonal antibody for the sensitive detection of the pathogen directly from plants. It was demonstrated that the immunocapture PCR (IC-PCR) was more sensitive than the conventional PCR and even more sensitive than indirect ELISA for the detection of the pathogen. Latently infected plants could be positively screened for the presence of the pathogen. Three sets of primers were designed from DNA probes that were reported to show some specificity to the pathovar dieffenbachiae. The use of all three sets of primers in a single reaction successfully amplified the three individual loci when bacterial DNA was used as a template. The multiplex PCR generated PCR profiles that could differentiate between the reference strains of X. axonopodis pv. dieffenbachiae from other control bacteria. The new primers could therefore be used both for the diagnosis of Anthurium blight in single PCR reactions and also for the profiling of Xanthomonas. pv. dieffenbachiae strains using the multiplex PCR technique.     

Copper resistance in Xanthomonas campestris pv. campestris affecting crucifers in Trinidad

Fifty-six native isolates collected in 12 farming districts of Trinidad and seven reference strains of Xanthomonas campestris pv. campestris were evaluated for resistance to copper in buffered (pH 7.0) and unbuffered (pH 5.6) nutrient agar media. All isolates and reference strains were pathogenic and elicited typical black rot symptoms on a susceptible variety of Brassica olearceae, ‘Copenhagen Market’. Thirty-four and thirty-three native isolates were highly resistant to copper (growth on?≥?200 ppm copper) in buffered and unbuffered media, respectively; however, all the reference strains were highly susceptible to copper. The mean minimum inhibition concentration for the 56 native isolates was 224.6 ppm copper indicating that high levels of copper resistance are present in X. campestris pv. campestris in Trinidad. The association between growth of the 56 isolates and seven reference stains on buffered and unbuffered media was strong (Pearson’s and Spearman’s r?=?0.93; P?<?0.01) suggesting that either medium can be used to evaluate resistance to copper in X. campestris pv. campestris. There was also a strong association between length of time of continuous applications of copper formulations to treat black rot disease and proportion of the native X. campestris pv. campestris with resistance to copper (Pearson’s r?=?0.96; Spearman’s r?=?0.93); however, there was no association between resistance to copper and aggressiveness at 10 days after inoculation.