Isoenzyme diversity in Xanthomonas campestris pv. mangiferaeindicae

A collection of 26 strains of Xanthomonas campestris pv. mangiferaeindicae isolated from three different host species in eight countries was investigated for variation in isozyme patterns. Three enzyme systems were analysed: esterase (EST), phosphoglucomutase (PGM) and superoxide dismutase (SOD). Four groups of strains were identified: nonpigmented strains isolated from mango and pepper-tree in Australia, Comores, India, Reunion Island, South Africa, and Taiwan; nonpigmented Brazilian strains from mango; nonpigmented strains from ambarella isolated in the French West Indies; heterogeneous yellow pigmented strains from mango (Brazil and Reunion Island). The value of isozyme profiling as markers of the pathogenicity groups in X. c . pv. mangiferaeindicae is discussed.     

Quantitative real-time polymerase chain reaction for bacterial enumeration and allelic discrimination to differentiate xanthomonas strains on citrus

ABSTRACT Quantitative real-time polymerase chain reaction (QRT-PCR) was developed for identification and enumeration of bacteria in citrus plant samples infected with Xanthomonas axonopodis pvs. citri and citrumelo, the cause of citrus bacterial canker (CBC) and citrus bacterial spot (CBS), respectively. Three sets of primers based on the pathogenicity gene (pth) in X. axonopodis pv. citri, a ribosomal gene in X. axonopodis pv. citrumelo, and the leucine-responsive regulatory protein (lrp) in both pathovars were combined with TaqMan probes and applied for specific strain detection and quantification. Calibration curves for bacterial abundance in plant samples obtained with the three primer-probe combinations were congruent with colony counts on plates of semiselective medium in most of the cases. However, apparent overestimation of bacterial cells by QRT-PCR indicated the presence of nonculturable or nonviable cells in some samples. In addition to quantification, the lrp primers and probes permitted differentiation by allelic discrimination of Xanthomonas strains infecting citrus tissues. This technique is based on the utilization of two probes that detect a single nucleotide difference in the target sequence between different strains and was validated with a collection of cultured Xanthomonas strains as well as tissue with CBC and CBS lesions. Allelic discrimination is demonstrated to be a more specific and sensitive protocol than previously developed PCR-based methods for strain identification and quantification.     

Diagnostic methods for phytopathogenic bacteria of stone fruits and nuts in COST 873

Different diagnostic methods used or developed in the EU-COST ² 873 project 'Bacterial diseases of stone fruits and nuts' are presented. The methods concern detection and identification of the plant pathogenic bacteria Xylella fastidiosa (EPPO A1 list), Xanthomonas arboricola pv corylina , X.a . pv. pruni , Pseudomonas syringae pv. persicae (A2 list pathogens), Agrobacterium tumefaciens , Brenneria nigrifluens and B. rubrifaciens , P. amygdali , P. avellanae , P.s. pv . avii , P.s. pv. morsprunorum , P.s . pv. syringae , X.a . pv. juglandis . Furthermore, a recently described xanthomonas species (proposed name X. translucens pv . pistachiae ), causing a new disease on pistachio, viz. Pistachio decline, in Australia and the recently renamed Xanthomonas citri pv. mangiferaeindicae on mango are included. The methods range from classical ones such as nutritional tests, use of (semi-)selective media, PCR, fatty acid analysis, serology and pathogenicity tests as well as (more) modern ones such as free flow capillary electrophoresis, real-time PCR, rep-PCR, fAFLP and sequencing of open reading frames (ORFs) and/or housekeeping genes such as gyrB and rpoD . The usefulness of these methods are outlined and reference made to publications where they were successfully used. Development of useful (molecular) tools are also indicated. Whole genome sequencing has been performed for Pantoea agglomerans (a relevant biocontrol agent) by the Swiss laboratory and initiated for X. a . pv. pruni by the French laboratory in cooperation with the Swiss and Italian laboratories and development of a microarray test has been initiated by the Swiss laboratory, Details of meetings and training programmes throughout the region are elaborated.     

Characterization of phenotypically distinct strains of Xanthomonas axonopodis pv. citri from Southwest Asia

Strains of Xanthomonas axonopodis pv. citri were isolated from Mexican lime (Citrus aurantifolia) trees in several countries in southwest Asia. These strains produced typical erumpent bacterial canker lesions on Mexican lime but not on grapefruit (C. paradisi). Lesions on grapefruit were watersoaked and blister-like in contrast to the typical erumpent lesions seen after artificial inoculation with all described pathotypes of X. axonopodis pv. citri. This group of strains hydrolysed gelatin and casein and grew in the presence of 3% NaCl as is typical of X. axonopodis pv. citri pathotype A. RFLP analyses and DNA probe hybridization assays also gave results consistent with X. axonopodis pv. citri pathotype A. Metabolic fingerprints prepared with the Biolog® system showed similarities as well as differences to X. axonopodis pv. citri pathotype A. In spite of the physiological and genetic similarities to pathotype A of X. axonopodis pv. citri, these strains had no or very little affinity for polyclonal antiserum prepared against any of the reference strains of X. axonopodis pv. citri and also did not react with monoclonal antibody A1, an antibody that detects all strains of pathotype A of X. axonopodis pv. citri. These strains were also insensitive to bacteriophage Cp3 like X. axonopodis pv. citri pathotype A and unlike X. axonopodis pv. citri pathotype B. We conclude that these strains, designated Xcc-A*, represent a variant of X. axonopodis pv. citri pathotype-A with pathogenicity limited to C. aurantifolia. The existence of extensive genotypic and phenotypic variation within pathotype A of X. axonopodis pv. citri was unexpected and further complicates the systematics of this species.     

Development of a variable number of tandem repeats typing scheme for the bacterial rice pathogen Xanthomonas oryzae pv. oryzicola

Xanthomonas oryzae pv. oryzicola is an important bacterial pathogen responsible for outbreaks of bacterial leaf streak (BLS) on rice, mostly occurring in Asia and parts of Africa. To better monitor epidemics and assess population structures, efficient tools that allow the precise identification and diagnosis of pathogenic populations are needed. In this study, we explored variable numbers of tandem repeats (VNTR) as a fast, reliable, and cost-effective molecular typing tool. Screening of three X. oryzae pv. oryzicola genome sequences (Philippine strain BLS256, Chinese strain GX01, and Malian strain MAI10) predicted 28 candidate VNTR loci. Primer pairs for polymerase chain reaction (PCR) amplification of all 28 loci were designed and applied to a panel of 20 X. oryzae pv. oryzicola strains originating from Asia and Africa. Sequencing of PCR amplicons revealed 25 robust and polymorphic VNTR loci that are shared among Asian and African X. oryzae pv. oryzicola strains. A dendrogram constructed from 25 VNTR loci indicated that most Asian strains are clearly discriminated from African strains. However, in agreement with previous reports, one strain from Mali is related to Asian strains, pointing to a possible introduction of Asian strains to the African continent. The new VNTR-based tool described here is useful for studies of population structures and epidemiological monitoring of X. oryzae pv. oryzicola.     

Genetic Diversity of Xanthomonas oryzae pv. oryzae Strains from Sri Lanka

ABSTRACT Sixty strains of Xanthomonas oryzae pv. oryzae, collected from 29 locations in Sri Lanka in 1995, were analyzed by restriction fragment length polymorphism using either polymerase chain reaction-amplified 16S and 23S rDNA or the repetitive DNA element IS1112 from X. oryzae pv. oryzae as hybridization probes. Two different ribogroups were observed in the Sri Lankan strains using rDNA probes, whereas five clusters were identified by the IS1112 probe. Bootstrap analysis revealed that the five clusters defined by IS1112 were relatively robust. Our results suggest that the Sri Lankan strains are phylogenetically composed of five different groups. Each cluster was partially associated with climatic conditions (intermediate zone and wet zone) and was related to groups based on ribotyping. Based on virulence analysis using 12 rice cultivars, each containing a single resistance gene, 14 pathotypes were identified among the Sri Lankan strains. All strains were virulent to resistance genes Xa1, Xa2, Xa4, Xa10, Xa11, and Xa14. Only one strain (pathotype 1) was virulent to all major resistance genes including Xa21, while strains of the other pathotypes were all avirulent to Xa21. A partial relationship was found between the determined phylogenetic groups using the IS1112 probe and pathotypes for all but two clusters. The results of this study will facilitate the further understanding of the population structure of X. oryzae pv. oryzae in Sri Lanka.     

Interaction of common bacterial blight bacteria with disease resistance quantitative trait loci in common bean

Common bacterial blight (CBB) of common bean (Phaseolus vulgaris L.) is caused by Xanthomonas campestris pv. phaseoli and X. fuscans subsp. fuscans, and is the most important bacterial disease of this crop in many regions of the world. In 2005 and 2006, dark red kidney bean fields in a major bean-growing region in central Wisconsin were surveyed for CBB incidence and representative symptomatic leaves collected. Xanthomonad-like bacteria were isolated from these leaves and characterized based upon phenotypic (colony) characteristics, pathogenicity on common bean, polymerase chain reaction (PCR) with X. campestris pv. phaseoli- and X. fuscans subsp. fuscans-specific primers, and repetitive-element PCR (rep-PCR) and 16S-28S ribosomal RNA spacer region sequence analyses. Of 348 isolates that were characterized, 293 were identified as common blight bacteria (i.e., pathogenic on common bean and positive in PCR tests with the X. campestris pv. phaseoli- and X. fuscans subsp. fuscans-specific primers), whereas the other isolates were nonpathogenic xanthomonads. Most (98%) of the pathogenic xanthomonads were X. campestris pv. phaseoli, consistent with the association of this bacterium with CBB in large-seeded bean cultivars of the Andean gene pool. Two types of X. campestris pv. phaseoli were involved with CBB in this region: typical X. campestris pv. phaseoli (P) isolates with yellow mucoid colonies, no brown pigment production, and a typical X. campestris pv. phaseoli rep-PCR fingerprint (60% of strains); and a new phenotype and genotype (Px) with an X. campestris pv. phaseoli-type fingerprint and less mucoid colonies that produced brown pigment (40% of strains). In addition, a small number of X. fuscans subsp. fuscans strains, representing a new genotype (FH), were isolated from two fields in 2005. Representative P and Px X. campestris pv. phaseoli strains, an FH X. fuscans subsp. fuscans strain, plus five previously characterized X. campestris pv. phaseoli and X. fuscans subsp. fuscans genotypes were inoculated onto 28 common bean genotypes having various combinations of known CBB resistance quantitative trait loci (QTL) and associated sequence-characterized amplified region markers. Different levels of virulence were observed for X. campestris pv. phaseoli strains, whereas X. fuscans subsp. fuscans strains were similar in virulence. The typical X. campestris pv. phaseoli strain from Wisconsin was most virulent, whereas X. campestris pv. phaseoli genotypes from East Africa were the least virulent. Host genotypes having the SU91 marker-associated resistance and one or more other QTL (i.e., pyramided resistance), such as the VAX lines, were highly resistant to all genotypes of common blight bacteria tested. This information will help in the development of CBB resistance-breeding strategies for different common bean market classes in different geographical regions, as well as the identification of appropriate pathogen genotypes for screening for resistance.     

Phenotypic and Genetic Diversity in Strains of Common Blight Bacteria (Xanthomonas campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscans) in a Secondary Center of Diversity of the Common Bean Host Suggests Multiple Introduction Events

ABSTRACT Common bacterial blight (CBB) disease of the common bean (Phaseolus vulgaris) is caused by Xanthomonas campestris pv. phaseoli and the brown-pigmented variant X. campestris pv. phaseoli var. fuscans. CBB first was described in Castilla y León County, Spain, in 1940, and is now a major constraint on common bean production. In this secondary center of diversity of the common bean, large-seeded Andean cultivars predominate, although medium-seeded Middle American cultivars also are grown. Xanthomonad-like bacteria associated with CBB in Castilla y León were characterized on the basis of carbohydrate metabolism, brown pigment production, genetic analyses (repetitive-element polymerase chain reaction [rep-PCR] and random amplified polymorphic DNA [RAPD]) and pathogenicity on cultivars representing the two common bean gene pools (Andean and Middle American). X. campestris pv. phaseoli was more prevalent (80%) than X. campestris pv. phaseoli var. fuscans (20%). Patterns of carbohydrate metabolism of Spanish CBB bacteria were similar to those of known strains; and only X. campestris pv. phaseoli var. fuscans strains utilized mannitol as a sole carbon source. rep-PCR and RAPD analyses revealed relatively little genetic diversity among Spanish X. campestris pv. phaseoli strains, and these strains were placed together with New World strains into a large cluster. Similar to other New World strains, representative Spanish X. campestris pv. phaseoli strains were highly pathogenic on bean cultivars of both gene pools, showing no gene pool specialization such as that found in certain East African strains. Genetic analyses and pathogenicity tests confirmed and extended previous results, indicating that these East African strains represent distinct xanthomonads that independently evolved to be pathogenic on common bean. X. campestris pv. phaseoli var. fuscans strains were more closely related and genetically distinct from X. campestris pv. phaseoli strains. However, two distinct clusters of X. campestris pv. phaseoli var. fuscans strains were identified, one having the most New World strains and the other having the most African strains. Spanish strains were placed in both clusters, but all strains tested were highly pathogenic on bean cultivars of both gene pools. Together, our results are consistent with multiple introductions of CBB bacteria into Spain. These findings are discussed in terms of breeding for CBB resistance and the overall understanding of the genetic diversity and evolution of CBB bacteria.     

Use of phages for identifying the citrus canker bacterium Xanthomonas campestris pv. citri in Taiwan

Phages CP115 and CP122, which were isolated from canker lesions on grapefruit and Liucheng sweet orange, respectively, showed a high degree of specificity with respect to lysis of test bacterial strains. When used jointly, they lysed 135 (97·8%) out of 138 Xanthomonas campestris pv. citri strains isolated from the canker lesions on leaves, twigs, and fruits of various citrus species, cultivars, and hybrids grown throughout Taiwan, but they did not lyse other X. campestris pathovars and other phytopathogenic bacteria, nor other bacteria isolated from soil, clinical or environmental samples. Of 252 CP115/CP122-sensitive and 78 CP115/CP122-resistant bacterial strains with colony characteristics typical of or similar to those of X. campestris pv. citri , isolated from canker lesions of various citrus plants in diverse growing regions in Taiwan, 250 (99·2%) and 76 (97·4%) strains were pathogenic and non-pathogenic, respectively, when inoculated into Liucheng sweet orange or Mexican lime. Thus, phages CP115 and CP122, when used jointly, appear to be applicable for identifying X. campestris pv. citri in Taiwan.     

PCR-mediated Detection of <Emphasis Type="Italic">Xanthomonas oryzae </Emphasis>pv. <Emphasis Type="Italic">oryzae </Emphasis>by Amplification of the 16S–23S rDNA Spacer Region Sequence

A detection method specific for Xanthomonas oryzae pv. oryzae, the pathogen responsible for bacterial blight of rice, was based on the polymerase chain reaction (PCR) and designed by amplifying the 16S–23S rDNA spacer region from this bacterium. The nucleotide sequence of the spacer region between the 16S and 23S rDNA, consisting of approximately 580-bp, from X. oryzae pv. oryzae, X. campestris pv. alfalfae, X. campestris pv. campestris, X. campestris pv. cannabis, X. campestris pv. citri, X. campestris pv. cucurbitae, X. campestris pv. pisi, X. campestris pv. pruni and X. campestris pv. vitians, was determined. The determined sequences had more than 95% identity. Therefore, a pair of primers, XOR-F (5′-GCATGACGTCATCGTCCTGT-3′) and XOR-R2 (5′-CTCGGAGCTATATGCCGTGC-3′) was designed and found to specifically amplify a 470-bp fragment from all strains of X. oryzae pv. oryzae isolated from diverse regions in Japan. No PCR product was amplified from X. campestris pathovars alfalfae, campestris, cannabis, carotae, cucurbitae, dieffenbachiae, glycines, pisi, pruni, vitians or zantedeschiae, except for pathovars citri, incanae and zinniae. The method could also detect the pathogen in infected rice leaves within 3 hr, at a detection limit of 4×10¹ cfu/ml. Received 17 December 1999/ Accepted in revised form 10 April 2000     

Genetic Diversity and Pathogenic Variation of Common Blight Bacteria (Xanthomonas campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscans) Suggests Pathogen Coevolution with the Common Bean

ABSTRACT Common bacterial blight (CBB), caused by Xanthomonas campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscans, is one of the most important diseases of common bean (Phaseolus vulgaris) in East Africa and other bean-growing regions. Xanthomonad-like bacteria associated with CBB in Malawi and Tanzania, East Africa, and in Wisconsin, U.S., were characterized based on brown pigment production, pathogenicity on common bean, detection with an X. campestris pv. phaseoli- or X. campestris pv. phaseoli var. fuscans-specific PCR primer pair, and repetitive element polymerase chain reaction (rep-PCR) and restriction fragment length polymorphism (RFLP) analyses. The common bean gene pool (Andean or Middle American) from which each strain was isolated also was determined. In Malawi, X. campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscans were isolated predominantly from Andean or Middle American beans, respectively. In Tanzania, X. campestris pv. phaseoli var. fuscans was most commonly isolated, irrespective of gene pool; whereas, in Wisconsin, only X. campestris pv. phaseoli was isolated from Andean red kidney beans. Three rep-PCR fingerprints were obtained for X. campestris pv. phaseoli strains; two were unique to East African strains, whereas the other was associated with strains collected from all other (mostly New World) locations. RFLP analyses with repetitive DNA probes revealed the same genetic diversity among X. campestris pv. phaseoli strains as did rep-PCR. These probes hybridized with only one or two fragments in the East African strains, but with multiple fragments in the other X. campestris pv. phaseoli strains. East African X. campestris pv. phaseoli strains were highly pathogenic on Andean beans, but were significantly less pathogenic on Middle American beans. In contrast, X. campestris pv. phaseoli strains from New World locations were highly pathogenic on beans of both gene pools. Together, these results indicate the existence of genetically and geographically distinct X. campestris pv. phaseoli genotypes. The rep-PCR fingerprints of X. campestris pv. phaseoli var. fuscans strains from East African and New World locations were indistinguishable, and were readily distinguished from those of X. campestris pv. phaseoli strains. Genetic diversity among X. campestris pv. phaseoli var. fuscans strains was revealed by RFLP analyses. East African and New World X. campestris pv. phaseoli var. fuscans strains were highly pathogenic on Andean and Middle American beans. Breeding for CBB resistance in East African beans should utilize X. campestris pv. phaseoli var. fuscans and New World X. campestris pv. phaseoli strains in order to identify germ plasm with the highest levels of resistance.     

Structure and Origin of Xanthomonas arboricola pv. pruni Populations Causing Bacterial Spot of Stone Fruit Trees in Western Europe

ABSTRACT Xanthomonas arboricola pv. pruni, the causal agent of bacterial spot on stone fruit, was found in 1995 in several orchards in southeastern France. We studied population genetics of this emerging pathogen in comparison with populations from the United States, where the disease was first described, and from Italy, where the disease has occurred since 1920. Four housekeeping genes (atpD, dnaK, efp, and glnA) and the intergenic transcribed spacer region were sequenced from a total of 3.9 kb of sequences, and fluorescent amplified fragment length polymorphism (FAFLP) analysis was performed. A collection of 64 X. arboricola pv. pruni strains, including 23 strains from France, was analyzed. The X. arboricola pv. pruni population had a low diversity because no sequence polymorphisms were observed. Population diversity revealed by FAFLP was lower for the West European population than for the American population. The same bacterial genotype was detected from five countries on three continents, a geographic distribution that can be explained by human-aided migration of bacteria. Our data support the hypothesis that the pathogen originated in the United States and subsequently has been disseminated to other stone-fruit-growing regions of the world. In France, emergence of this disease was due to a recent introduction of the most prevalent genotype of the bacterium found worldwide.     

Copper Resistance in Pseudomonas syringae Strains Isolated from Mango Is Encoded Mainly by Plasmids

ABSTRACT Bacterial apical necrosis of mango, elicited by Pseudomonas syringae pv. syringae, limits fruit production in southern Spain and Portugal. Examination of a collection of P. syringae pv. syringae isolates for copper resistance showed that 59% were resistant to cupric sulfate. The survey of a mango orchard revealed an increase in frequencies of copper-resistant bacteria after repeated treatments with Bordeaux mixture. These data suggest that selection of copper-resistant strains could be a major reason for control failures following management with copper bactericides. Most copper-resistant isolates harbored plasmids, although the majority of them contained a 62-kb plasmid that also was present in copper-sensitive strains. The 62-kb plasmids were differentiated by restriction enzyme analysis and hybridization to copABCD DNA. The most frequently found copper-resistant plasmid type (62.1) was transferable by conjugation. Southern blot hybridizations showed that genetic determinants partially homologous to copABCD were present in all the copper-resistant strains examined, and usually were associated with plasmids; these determinants were not detected in copper-sensitive strains. The selective pressure exerted by copper bactericide sprays on the diversity of copper resistance determinants in bacterial populations of mango is discussed.     

Pathogenic and Genetic Relatedness Among Xanthomonas axonopodis pv. allii and Other Pathovars of X. axonopodis

ABSTRACT Xanthomonas axonopodis pv. allii is phenotypically and genetically diverse and its relationship to other X. axonopodis pathovars within DNA homology group 9.2 is unknown. In growth chamber experiments, disease symptoms were produced on onion only by inoculation with X. axonopodis pv. allii. Citrus bacterial spot symptoms were induced by X. axonopodis pvs. alfalfae, itrumelo, and allii on Duncan grapefruit and key lime. X. axonopodis pv. allii multiplication and persistence in Duncan grapefruit were equal to those of an aggressive strain of X. axonopodis pv. citrumelo, but populations of X. axonopodis pvs. alfalfae, betlicola, citrumelo, phaseoli, and vesicatoria were 1.3 to 4.0 log units less than X. axonopodis pv. allii in onion. Genomic fingerprinting by repetitive sequence- based polymerase chain reaction demonstrated that X. axonopodis pvs. allii, alfalfae, and citrumelo are distinct from other Xanthomonas species and X. axonopodis pathovars, but these pathovars were indistinguishable from each other. Three genotype groups were apparent among DNA homology group 9.2 strains, and generally correspond to the aggressiveness and genotype groups previously described for X. axonopodis pv. citrumelo. X. axonopodis pvs. allii, alfalfae, and citrumelo appear to have recently diverged from a common ancestral strain.     

柑桔溃疡病内生拮抗细菌Bc51的研究

 从中国南宁柑桔叶片中分离到对柑桔溃疡病菌有拮抗作用的细菌菌株Bc51。根据16S rDNA序列同源性、形态学特征和生理生化反应,将该菌株鉴定为洋葱伯克霍尔德氏菌(Burkholderia cepacia)。温度、pH值和培养基对洋葱伯克霍尔德氏菌抑制柑桔溃疡病菌生长的能力有显著影响。在温室测试中,观察到60.3%柑桔溃疡病斑的形成受到洋葱伯克霍尔德氏菌抑制。连续8次在人工培养基上转代培养,洋葱伯克霍尔德氏菌对柑桔溃疡病菌生长的抑制力没有发生明显改变。洋葱伯克霍尔德氏菌对植物病原菌有较宽的抑菌谱,表明除柑桔溃疡病外,该菌对其它作物病害的防治也具有潜在的应用价值。     

Measuring the Genetic Diversity of Xanthomonas axonopodis pv. manihotis Within Different Fields in Colombia

ABSTRACT Cassava bacterial blight, caused by Xanthomonas axonopodis pv. manihotis, is a widespread disease that affects cassava (Manihot esculenta). We collected 238 X. axonopodis pv. manihotis strains by intensively sampling single fields in four edaphoclimatic zones (ECZs) in Colombia. DNA polymorphism of different X. axonopodis pv. manihotis populations was assessed by restriction fragment length polymorphism (RFLP) analyses, repetitive sequence-based polymerase chain reaction (rep-PCR), and amplified fragment length polymorphism (AFLP) assays. Genetic diversity, phenetic relationships among strains, and the coefficient of genetic differentiation were determined. All strains were tested for aggressiveness on the susceptible cassava cv. MCOL 1522. Strains were also tested for virulence on cassava differentials adapted to the strains' respective ECZs. Our study showed that the Colombian X. axonopodis pv. manihotis population has a high degree of genetic diversity. The hierarchical analysis of diversity showed genotypic differentiation at all levels, among ECZs, among fields within ECZs, and among strains within fields planted to several cassava genotypes. New RFLP haplotypes were detected, leading to the characterization of a new pathotype. Dendrograms from AFLP were more robust than those from RFLP data. A close association between the strains' geographical origin and DNA polymorphism was obtained using RFLP and AFLP data. We suggest that the host played a role in causing pathogen differentiation.     

Genetic,biochemical and pathogenic diversity of Pseudomonas syringae pv. pisi strains

Pseudomonas syringae pv. pisi is a seedborne pathogen distributed worldwide that causes pea bacterial blight. Previous characterization of this pathogen has been carried out with relatively small and/or geographically limited samples. Here, a collection of 91 strains are examined that include strains from recent outbreaks in Spain (53 strains) and from 14 other countries, and that represent all races and the new race 8, including the type race strains. This collection was characterized on the basis of 55 nutritional tests, genetic analysis (rep‐PCR, amplification of AN3 and AN7 specific markers, and multilocus sequence typing (MLST)) and pathogenicity on the differential pea cultivars to identify races. Principal component analysis and distance dendrograms confirm the existence of two genetic lineages within this pathovar, which are clearly discriminated by the AN3/AN7 markers, rep‐PCR and MLST. Strains from races 1 and 7 amplified the AN3 marker; those from races 2, 6 and 8 amplified AN7, while strains of races 3, 4 and 5 amplified either AN3 or AN7. Nevertheless, strains were not grouped by race type by any of the genetic or biochemical tests. Likewise, there was no significant association between metabolic and/or genetic profiling and the geographical origin of the strains. The Spanish collection diversity reflects the variability found in the worldwide collection, suggesting multiple introductions of the bacteria into Spain by contaminated seed lots.     

抑制植物病原细菌的植物筛选

以3种重要的植物病原细菌—辣椒青枯病菌(Ralstonia solanacearum)、柑橘溃疡病菌(Xanthomonas citri)和大白菜软腐病菌(Erwinia carotovorapv.carotovora)为供试菌,对43种植物甲醇提取物进行离体抑菌活性测定。研究结果表明,漆树对辣椒青枯病菌抑菌活性最强,其次是金秀清明茶;抑制柑橘溃疡病菌活性最高的植物有漆树和十大功劳;对大白菜软腐病菌没有筛选到抑菌活性较好的植物;垫状卷柏、七叶一枝花、少花龙葵、水半夏和豆瓣菜粗提物对3种植物病原细菌均无抑制作用。