Identification and Origin of Xanthomonas campestris pv. campestris Races and Related Pathovars

ABSTRACT One hundred sixty-four isolates of Xanthomonas campestris pv. campestris and other X. campestris pathovars known to infect cruciferous hosts (X. campestris pvs. aberrans, raphani, armoraciae, and incanae) were inoculated onto a differential series of Brassica spp. to determine both pathogenicity to brassicas and race. Of these, 144 isolates were identified as X. campestris pv. campestris and grouped into six races, with races 1 (62%) and 4 (32%) being predominant. Other races were rare. The remaining 20 isolates from brassicas and other cruciferous hosts were either nonpathogenic or very weakly pathogenic on the differential series and could not be race-typed. Five of these isolates, from the ornamental crucifers wallflower (Cheiranthus cheiri), stock (Matthiola incana) and candytuft (Iberis sp.), showed clear evidence of pathovar-like specificity to the hosts of origin. A gene-for-gene model based on the interaction of four avirulence genes in X. campestris pv. campestris races and four matching resistance genes in the differential hosts is proposed. Knowledge of the race structure and worldwide distribution of races is fundamental to the search for sources of resistance and for the establishment of successful resistance breeding programs.     

Pathogenicity assays restrict the species Xanthomonas campestris into three pathovars and reveal nine races within X. campestris pv. campestris

The species Xanthomonas campestris (Vauterin) groups bacteria associated with cruciferous plants. In order to clarify and refine the pathovar and race structures within X . campestris , 47 representative strains of six pathovars were characterized for their pathogenicity on a large host range of Brassicaceae, including all original hosts. Three diseases were observed on tested plants: (i) black rot disease on cruciferous plants; it was proposed that all strains causing black rot on at least one cruciferous plant be grouped in the single pathovar X . c . pv. campestris ; (ii) leaf spot disease caused by X . c . pv. raphani on hosts belonging to the Brassicaceae and Solanaceae; the sequenced strain 756C identified as X . c . pv. armoraciae was included in this pathovar and the existence of another leaf spot disease caused by X . c . pv. armoraciae was not supported; and (iii) bacterial blight of garden stocks caused by X . c . pv. incanae . No plants susceptible to X . c . pv. barbareae were found. Strains that did not induce any symptom on cruciferous plants tested, including their original hosts, were removed from the pathovar scheme and were named X . campestris only. Three new races were described in addition to the six races previously described within X . c . pv. campestris . The sequenced strains ATCC 33913 (CFBP 5241) and Xcc 8004 (CFBP 6650) belonged to race 3 and to race 9 (one of the new races described), respectively.     

Movement of Xanthomonas campestris pv. vitians in the stems of lettuce and seed contamination

Xanthomonas campestris pv. vitians , the causal agent of bacterial leaf spot of lettuce (BLS), can be seedborne, but the mechanism by which the bacteria contaminates and/or infects lettuce seed is not known. In this study, the capacity of X. campestris pv. vitians to enter and translocate within the vascular system of lettuce plants was examined. The stems of 8- to 11-week-old lettuce plants were stab-inoculated, and movement of X. campestris pv. vitians was monitored at various intervals. At 4, 8, 12 and 16 h post-inoculation (hpi), X. campestris pv. vitians was recovered from 2 to 10 cm above (depending on stem length) and 2 cm below the inoculation site. Xanthomonas campestris pv. vitians was also recovered from surface-disinfested stem sections of spray-inoculated plants. Together, these results are consistent with X. campestris pv. vitians invading and moving systemically within the vascular system of lettuce plants. To investigate the mechanism of seed contamination, lettuce plants at the vegetative stage of growth were spray-inoculated with X. campestris pv. vitians and allowed to develop BLS. Seed collected from these plants had a 2% incidence of X. campestris pv. vitians external colonization, but no bacteria were recovered from within the seed.     

Races of Xanthomonas campestris pv. vesicatoria overcoming the gene Bs2 for bacterial spot resistance in pepper, prevalent on Capsicum chinense in Barbados and Grenada and weakly pathogenic on bell pepper and tomato in the field

A total of 404 isolates of Xanthomonas campestris pv. vesicatoria , obtained from Capsicum chinense cv. West Indian Red grown in Barbados and Grenada, were differentiated into pathogenic races, and of these, 96 were tested also for selected taxonomic group phenotypes. The response of C. chinense to infection by several X. campestris pv. vesicatoria races and the contribution of races isolated from this cultivar to severity of bacterial spot of bell pepper and tomato were also investigated. P4T2, P5T2 and P6T2 were the predominant races of X. campestris pv. vesicatoria isolated from C. chinense grown in Grenada, whereas nine races (T1, P4, P6, P0T2, P1T2, P4T1, P4T2, P6T1 and P6T2) were isolated in Barbados. Race P4T2 comprised 46.0 and 71.4% of the isolates from Barbados and Grenada, respectively. The 96 isolates, all of which overcame resistance conferred by the gene Bs2 , shared taxonomic group B strain characteristics, including the presence of the β-protein band, positive amylolytic activity and inability to oxidize cis -aconitate. The C. chinense cv. West Indian Red was susceptible only to races of X. campestris pv. vesicatoria that can overcome Bs2 gene resistance. Of six such races identified in Barbados, only P4T1, P4T2 and P6T1 affected bacterial spot-susceptible bell pepper or tomato in the field, and they amounted to only 1.5–2.1% of each sample of isolates from these plant species. Moreover, they were confined to the smallest bacterial spot lesions. Bell pepper was most severely affected by combinations of races T1 with P3T2 and T2 with P0T1, and tomato by race T1 only and combinations of races P0T1 with P0T2 and P1T1 with P1T0, all of which prevailed in the field despite selection against them by C. chinense cv. West Indian Red.     

Bacterial spot of capsicum and tomato in Yugoslavia

The causal agent of bacterial spot of capsicum and tomato grown in different regions in Yugoslavia was investigated. Isolations were made from diseased material collected in recent years. The biochemical and physiological characteristics of isolated bacteria were studied by standard bacteriological tests. The race of the pathogen was determined on differential cultivars of capsicum and tomato. The causal agent of the disease was identified according to the concepts of the time as Xanthomonas campestris pv. vesicatoria. Strains isolated from diseased capsicum were non-pectolytic and non-amylolytic, and did not infect tomato plants. According to the reaction of capsicum cv. Early Calwonder and its isogenic lines, these strains belonged to'pepper races'1 and 3 of X. vesicatoria. Tomato strains showed pectolytic and amylolytic activity and were not pathogenic to capsicum. Accordingly, the capsicum strains could now be considered to be X. axonopodis pv. vesicatoria and the tomato strains X. vesicatoria.     

The dynamics of homologous and heterologous interactions between rice and strains of Xanthomonas campestris

Lesion development, bacterial multiplication and spread were measured in leaves of cultivars of rice containing different Xa (resistance) genes, following inoculation with different races of the bacterial leaf blight pathogen. Xanthomonas campestris pv. oryzae. Both compatible and incompatible races possessed the ability to colonize rice plants. The difference between compatible and incompatible host pathogen combinations appeared to be mainly in symptom production since multiplication rates and spread were very similar until after the onset of symptoms. No form of HR (hypersensitive response) was observed. The ability of incompatible races to modify host reaction in dual-inoculation was dependent on the genotype of the host plant. The heterologous non-pathogen of rice X. campestris pv. campestris produced few symptoms, failed either to multiply or spread within rice leaves and was unable to induce any marked cross-protection against homologous pv. oryzae strains in dual-inoculation experiments.     

Sensitive real-time PCR detection of Xanthomonas fragariae in strawberry plants

Xanthomonas fragariae , the causal agent of angular leaf spot on strawberry, is a quarantine organism in strawberry propagation material in the European Union. For the reliable screening of planting material for latent infections, a real-time PCR assay based on Taqman® chemistry for the detection of X. fragariae was developed. Primers and probe sequences were based on a DNA fragment amplified by a previously reported X. fragariae -specific technique. The sequence of this genomic fragment had no significant similarity with any published GenBank sequence. Specificity of the designed assay was tested with an extended range of X. fragariae collection strains and isolates, with other Xanthomonas spp. and with unidentified bacterial isolates from strawberry plants. A nested PCR, which until now was the reference method for sensitive detection in planta , cross-reacted with the reference strain of Xanthomonas campestris pv. campestris . In combination with an elaborated DNA extraction procedure, the Taqman® PCR enabled reliable detection down to 300 colony forming units in a 100 mg strawberry leaf sample. The assay offers a new tool for epidemiological research and for sanitary control of plant material with low level or latent infections of X. fragariae .     

辣椒、番茄细菌性疮痂病及生理小种鉴定

 近3年,从北京、山西、内蒙、新疆和云南等地的辣椒和番茄病株上分离到19个菌株,经致病性测定和细菌学鉴定,确定这19个菌株为甘蓝黑腐黄单胞菌疮痂致病变种(Xanthomonas campestris pv.vesicatoria(Doidge) Dye,1978)。供试19个菌株在国内首次采用国际标准鉴别寄主进行了生理小种鉴定。其中,3个菌株为番茄小种1(XcvT race1),仅存在于北京地区,其它16个菌株均属于辣椒-番茄小种3(XcvPT race3),分布广,为我国优势小种。     

Detection and identification of seed-borne pathogenic bacteria of imported tomato seeds in Egypt

Imported tomato seed lots of different cultivars were assayed for the presence of seed-borne bacterial pathogens. The liquid assay method was used for detection of the bacteria, and seed extracts were plated on different semi-selective media. Pseudomonas corrugata and Xanthomonas campestris pv. vesicatoria were detected in 14.7% and 12% of the seed samples tested respectively. These pathogens were identified by means of biochemical, physiological and pathogenicity tests as well as the Biolog GN Microplate System for X. campestris pv. vesicatoria. Both P. corrugata and X. campestris pv. vesicatoria were more easily identified on Tween B and CKTM media than on other media. This is the first report of the occurrence of these important pathogens on tomato seeds in Egypt.     

A rapid bioassay for screening rhizosphere microorganisms for their ability to induce systemic resistance

ABSTRACT We developed a rapid and miniaturized bioassay for screening large numbers of rhizosphere microorganisms for their ability to induce systemic resistance to bacterial leaf spot of radish caused by Xanthomonas campestris pv. armoraciae. In this bioassay, Pantoea agglomerans strain E278Ar controlled symptoms of disease as effectively as 2,6-dichloroisonicotinic acid when applied to the roots of seedlings produced in growth pouches in a soilless system. E278Ar essentially did not migrate from seedling roots to the foliage. This suggests that induction of systemic resistance could best explain the observed reduction in disease severity. Three mini-Tn5Km-induced mutants of strain E278Ar were isolated that had lost the ability to induce resistance. The bioassay also was used to demonstrate that the fungal biocontrol agent Trichoderma hamatum strain 382 induces systemic resistance in radish. The bioassay required only 14 to 18 days from seeding until rating for disease severity, which is 10 to 14 days less than earlier bioassays.     

Assessment of genetic diversity of Xanthomonas campestris pv. campestris isolates from Israel by various DNA fingerprinting techniques

Three molecular typing methods were used to investigate genetic diversity among Xanthomonas campestris pv. campestris isolates obtained in Israel and others previously obtained from different geographical locations (collection isolates). Using pulsed-field gel electrophoresis (PFGE), amplified fragment length polymorphism (AFLP) and repetitive sequence-based PCR (rep-PCR), 22 different isolates were divided into 11, 12 and 13 differentiated genotypes, respectively. All collection isolates yielded different genotypes and, among the isolates from Israel, several new genotypes were found. These findings not only support the observed heterogeneity within X. campestris pv. campestris , but also suggest that variability at the genomic level in this pathovar is higher than previously estimated. Moreover, while previous studies suggested that PCR patterns obtained with integron-specific primers are conserved in most X. campestris pathovars, PCR patterns of this element yielded four different types among the X. campestris pv. campestris isolates tested, thus supporting the relatively high diversity in this pathovar. Although differences in pathogenicity were observed among isolates, assays using cauliflower and radish did not indicate a correlation between pathogenicity and genotype.     

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.     

Inheritance of Race-Specific Resistance to Xanthomonas campestris pv. campestris in Brassica Genomes

ABSTRACT The inheritance of resistance to three Xanthomonas campestris pv. campestris races was studied in crosses between resistant and susceptible lines of Brassica oleracea (C genome), B. carinata (BC genome), and B. napus (AC genome). Resistance to race 3 in the B. oleracea doubled haploid line BOH 85c and in PI 436606 was controlled by a single dominant locus (Xca3). Resistance to races 1 and 3 in the B. oleracea line Badger Inbred-16 was quantitative and recessive. Strong resistance to races 1 and 4 was controlled by a single dominant locus (Xca1) in the B. carinata line PI 199947. This resistance probably originates from the B genome. Resistance to race 4 in three B. napus lines, cv. Cobra, the rapid cycling line CrGC5, and the doubled haploid line N-o-1, was controlled by a single dominant locus (Xca4). A set of doubled haploid lines, selected from a population used previously to develop a restriction fragment length polymorphism map, was used to map this locus. Xca4 was positioned on linkage group N5 of the B. napus A genome, indicating that this resistance originated from B. rapa. Xca4 is the first major locus to be mapped that controls race-specific resistance to X. campestris pv. campestris in Brassica spp.     

Methods to reduce the spread of the black rot pathogen,Xanthomonas campestris pv. campestris,in brassica transplants

Journal of Plant Diseases and Protection - Black rot of Brassica spp. caused by the bacterial pathogen Xanthomonas campestris pv. campestris (XCC), is a seedborne disease. Because the pathogen can...     

水稻品种(组合)抗白叶枯病基因初探

 用菲律宾6个白叶枯病菌系(小种),将95个水稻品种(品系)划分为5个品种类群,为今后开展品种抗病性的基因分析提供了必要的条件。通过测试,提出舟松62、二九丰(早籼) 城特232、T₈₅₂₈、H₁₀₁、6003、T₈₈₅₀₆、T₈₈₅₁₇、R₈₉₅、绍糯₈₈₄₃、丙₈₈₁₅₁、台₂₀₂、T₈₈₅₂₂(晚粳)等13个具有广谱抗性的品种(系),可作杂交亲本利用。     

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.     

Discrimination of <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis> races among strains from northwestern Spain by <Emphasis Type="Italic">Brassica</Emphasis> spp. genotypes and rep-PCR

Black rot, caused by Xanthomonas campestris pv. campestris (Xcc) is a severe seedborne disease of Brassica crops around the world. Nine races are recognized, being races 1 and 4 the most aggressive and widespread. The identification of Xcc races affecting Brassica crops in a target area is necessary to establish adequate control measures and breeding strategies. The objectives of this study were to isolate and identify Xcc strains from northwestern Spain by using semi-selective medium and pathogenicity tests, determine the existing races of Xcc in this area by differential series of Brassica spp., and evaluate the use of repetitive DNA polymerase chain reaction-based fingerprinting (rep-PCR) to differentiate among the nine existing Xcc races. Seventy five isolates recovered from infected fields were identified as Xcc. Race-typing tests determined the presence of the following seven pathogen races: 1, 4, 5, 6, 7, 8 and 9. Race 4 was the most frequent in Brassica oleracea and race 6 in Brassica rapa crops, therefore breeding should be focussed in obtaining resistant varieties to both races. Cluster analysis derived from the combined fingerprints showed four groups, but no clear relationship to race, crop or geographical origin was found. Rep-PCR analysis was found not to be a reliable method to discriminate among Xcc races, therefore race typing of Xcc isolates should be done by using the differential series of Brassica spp. genotypes or another alternative approach.     

Rapd Pcr-based differentiation of Xanthomonas campestris pv. phaseoli and Xanthomonas campestris pv. phaseoli var. fuscans

A RAPD PCR-based method was used to differentiate between isolates of Xanthomonas campestris pv. phaseoli and Xanthomonas campestris pv. phaseoli var. fuscans. Using random primer OP-G11, a single, high intensity band of 820 bp was amplified from DNAs of all X. c. pv. phaseoli var. fuscans isolates, while multiple amplification products of varying sizes were generated from X. c. pv. phaseoli DNAs. Whereas RAPD PCR differentiation gave an unambiguous result in under 4 h, standard differentiation by recording the production of a brown pigment by X. c. pv. phaseoli var. fuscans isolates took up to 7 days and showed variation both between isolates and between media. The unequivocal nature of the RAPD PCR method was demonstrated when isolate 408, originally classified as X. c. pv. phaseoli var. fuscans, failed to produce the 820 bp band typical of X. c. pv. phaseoli var. fuscans isolates, and after also failing to produce a brown pigment, was re-classified as X. c. pv. phaseoli.     

Isolation and characterization of rhizobacteria from composts that suppress the severity of bacterial leaf spot of radish

ABSTRACT Composts can induce systemic resistance in plants to disease. Unfortunately, the degree of resistance induced seems highly variable and the basis for this effect is not understood. In this work, only 1 of 79 potting mixes prepared with different batches of mature, stabilized composts produced from several different types of solid wastes suppressed the severity of bacterial leaf spot of radish caused by Xanthomonas campestris pv. armoraciae compared with disease on plants produced in a nonamended sphagnum peat mix. An additional batch of compost-amended mix that had been inoculated with Trichoderma hamatum 382 (T(382)), which is known to induce systemic resistance in plants, also suppressed the disease. A total of 11 out of 538 rhizobacterial strains isolated from roots of radish seedlings grown in these two compostamended mixes that suppressed bacterial leaf spot were able to significantly suppress the severity of this disease when used as inoculum in the compost-amended mixes. The most effective strains were identified as Bacillus sp. based on partial sequencing of 16S rDNA. These strains were significantly less effective in reducing the severity of this disease than T(382). A combined inoculum consisting of T(382) and the most effective rhizobacterial Bacillus strain was less effective than T(382) alone. A drench applied to the potting mix with the systemic acquired resistance-inducing chemical acibenzolar-S-methyl was significantly more effective than T(382) in several, but not all tests. We conclude that systemic suppression of foliar diseases induced by compost amendments is a rare phenomenon. Furthermore, inoculation of compost-amended potting mixes with biocontrol agents such as T(382) that induce systemic resistance in plants can significantly increase the frequency of systemic disease control obtained with natural compost amendments.