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1.
A semiselective medium was developed for isolating Xanthomonas campestris pv. musacearum ( Xcm ) from infected banana plants, soil and insect vectors. The new medium was named cellobiose-cephalexin agar (CCA) and it contained (L−1): 1 g yeast extract, 1 g glucose, 1 g peptone, 1 g NH4Cl, 1 g MgSO4·7H2O, 3 g K2HPO4, 1 g beef extract, 10 g cellobiose, 14 g agar, 40 mg cephalexin, 10 mg 5-fluorouracil and 120 mg cycloheximide. The medium was evaluated for selectivity using 21 bacterial isolates and for plating efficiency using Xcm . The bacterial isolates included a soilborne Xanthomonas species and three pathogenic Xanthomonas strains that infect cassava, cabbage and beans. Although the plating efficiency of Xcm on CCA was lower (59%) than on non-selective yeast extract peptone glucose agar (YPGA), its selectivity was significantly higher, averaging 60 and 82%, when isolating from banana fruits and soil, respectively. CCA was also superior when isolating Xcm from insect vectors, with selectivity of 48–75%, compared with 8–17% on YPGA. Xanthomonas campestris pv. phaseoli did not grow on CCA, while X. campestris pv. campestris and X. axonopodis pv. manihotis grew, but their colonies were smaller than those of Xcm . Twenty-nine out of 33 suspected Xcm strains isolated from plants, soil and insects using CCA were pathogenic when inoculated onto banana plants, indicating that CCA can be a reliable tool in isolating Xcm populations. The medium should prove useful in studies on ecology, epidemiology and management of the banana bacterial wilt pathogen that is currently ravaging bananas in East and Central Africa.  相似文献   

2.
Cotyledons of resistant and susceptible cotton ( Gossypium hirsutum ) cultivars were inoculated artificially with four isolates of Xanthomonas campestris pv. malvacearum from Africa (H V1, HV3, H V7 and Sudan) and USA race 18. Each isolate was used as single inoculum and in combinations of mixed inoculum. Disease reactions were graded 15 days after inoculation on a scale of I (immunity) to 10 (fully susceptible). Inoculation with HVI alone produced the highest disease grade of all inoculum treatments. When HVI was included in a mixed inoculum, disease grades were greatly reduced compared to HVI alone. Disease grades were highest for the inoculum mixture of the most virulent isolates HVI and race 18, but were still reduced compared to those from HVI alone. The efficiency of selection when screening cotton germplasm for bacterial blight resistance may be reduced if the highly virulent HVI isolate is included in an inoculum mixture composed of non-virulent isolates.  相似文献   

3.
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4.
ABSTRACT The development and genetic characterization of four near-isogenic lines (NILs) of cotton (Gossypium hirsutum) is described herein. Each line contains a single, but different, gene for resistance to bacterial blight caused by Xanthomonas campestris pv. malvacearum. The lines were derived using at least six backcrosses to the susceptible recurrent parent 'Acala 44', followed by single plant-progeny row selection for uniformity. The NILs are homozygous for the B(2), B(4), B(In), or b(7) genes and are designated as AcB(2), AcB(4), AcB(In), and Acb(7), respectively. In the 'Acala 44' background, B(2), B(4), and B(In) are partially dominant genes; b(7) is partially recessive. Relative strengths of resistance conferred by those genes toward race 1 of the pathogen were B(4) b(7)>B(In) B(2). B(4), B(In), and b(7) each conferred resistance toward X. campestris pv. malvacearum carrying a single avirulence gene, whereas B(2) was less specific.  相似文献   

5.
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.  相似文献   

6.
Seven races of Pseudomonas syringae pv. pisi were distinguished using eight differential cultivars of pea (Pisum sativum). Segregation among F2 populations of crosses between differential cultivars sequentially inoculated with races of P.s. pv. pisi provided evidence for four and possibly six putative resistance(R)/avirulence(A) gene pairs. R1, R2 and R3 are dominant resistance alleles at single loci, R4 is a dominant allele at a single locus which exhibits variable expression possibly dependent on genetic background. There is evidence that R3 and R4 are at linked loci. Homology tests provided proof of the occurrence of the alleles R2, R3 and R4 in more than one cultivar. Two other alleles, R5 and R6, were postulated to explain the observed segregation ratios in certain crosses.
It can be inferred that P.s. pv. pisi races 2, 3 and 4 each carry a different single a virulence gene, race 6 carries no apparent avirulence genes, and race 7 carries at least A2, A3 and A4. Race 1 carries Al, A3, A4 and possibly A6; race 5 carries A2, A4 and possibly A5 and A6.  相似文献   

7.
An enzyme-linked immunosorbent assay (ELISA) was standardized for detecting Xanthomonas campestris pv. undulosa (Xcu) in plant tissues. Antiserum prepared against somatic antigens of Xcu reacted with cells of pathovars undulosa, cerealis, translucens and phleipratensis , but not with other bacterial species belonging to the genera Xanthomonas, Pseudomonas, Agrobacterium, Clavibacter , and Erwinia. The lower limit of detection of pure cultures was 5 × 103 cfu/ml. A semi-selective enrichment broth (SSEB) improved the recovery of Xcu in cultures mixed with contaminating bacteria commonly found on wheat seeds. In ELISA tests the enriched samples gave two- to three-fold increases in A405nm readings when viable cells of Xcu were present. By enrichment, X. campestris pathovars undulosa, cerealis, translucens and phleipratensis were detected in samples that originally had less than 5 × 102 cfu/ml. Semi-selective enrichment combined with ELISA (SSEB-ELISA) allowed for determination of the percentages of infestation of wheat seed lots. Potential seedling infection (PSI) of naturally infested wheat seed lots was obtained by growing seed samples in the greenhouse under conditions optimal for disease development. Three methods were evaluated for their capacity to estimate the PSI: ELISA, combined SSEB and ELISA, and direct plating onto semi-selective XTS agar. Percentages of seed infestation determined by combined SSEB and ELISA resulted in a highly significant correlation with the PSI (r = 0·87, P × 005), whereas determinations made by ELISA or direct plating onto XTS did not significantly correlate with the PSI determined in the greenhouse. This test may constitute a convenient tool for fast initial screening of wheat seed lots in wheat certification programmes.  相似文献   

8.
ABSTRACT Twenty-five Xanthomonas isolates, including some isolates received as either X. campestris pv. armoraciae or pv. raphani, caused discrete leaf spot symptoms when spray-inoculated onto at least one Brassica oleracea cultivar. Twelve of these isolates and four other Xanthomonas isolates were spray- and pin-inoculated onto 21 different plant species/cultivars including horseradish (Armoracia rusticana), radish (Raphanus sativus), and tomato (Lycopersicon esculentum). The remaining 13 leaf spot isolates were spray-inoculated onto a subset of 10 plant species/cultivars. The leaf spot isolates were very aggressive on several Brassica spp., radish, and tomato causing leaf spots and dark sunken lesions on the middle vein, petiole, and stem. Based on the differential reactions of several Brassica spp. and radish cultivars, the leaf spot isolates were divided into three races, with races 1 and 3 predominating. A differential series was established to determine the race-type of isolates and a gene-for-gene model based on the interaction of two avirulence genes in the pathogen races and two matching resistance genes in the differential hosts is proposed. Repetitive-DNA polymerase chain reaction-based fingerprinting was used to assess the genetic diversity of the leaf spot isolates and isolates of closely related Xanthomonas pathovars. Although there was variability within each race, the leaf spot isolates were clustered separately from the X. campestris pv. campestris isolates. We propose that X. campestris isolates that cause a nonvascular leaf spot disease on Brassica spp. should be identified as pv. raphani and not pv. armoraciae. Race-type strains and a neopathotype strain for X. campestris pv. raphani are proposed.  相似文献   

9.
Two pigment-protein complexes extracted from the cell membrane of Xanthomonas campestris pv. juglandis with 2% Triton X-100 were separated from other membrane proteins by electrophoresis on a 10%., non-denaturing discontinuous polyacrylamide gel. One pigment-protein complex band was distinct, while the other was diffuse. The apparent Mr of the protein from the distinct pigment-protein band was 16400, while the protein in the diffuse band had an apparent Mr of about 45000. The protein in the distinct band consisted of 13 amino acids of which 10% were aromatic, 12% hydroxy, 16% basic, 16% acidic and 46% non-polar. Polyclonal antibody, against the distinct protein, was used to assay for cross-reactivity with cell wall and membrane proteins of 23 bacterial species by the Ouchterlony double-diffusion assay. Seven of the bacteria, representing seven genera, cross-reacted with the antibody, suggesting that a serologically-related, pigment-associated protein is commonly distributed among bacteria and which, unlike the pigment, may limit its use as a chemotaxonomic marker for Xanthomonas .  相似文献   

10.
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.  相似文献   

11.
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.  相似文献   

12.
Twenty strains of Xanthomonas campestris pv. campestris (Xcc) were isolated from two major crucifer-growing valleys, Chitwan and Kathmandu in Nepal and characterized by biochemical and pathogenicity tests. Strains were homogeneous in bacteriological characteristics. The ability of a strain to induce high or low disease severity index (DSI) on three host plants, broccoli, cabbage, and cauliflower, was interpreted as virulence. Strains that were associated with high or low virulence were significantly different (P>0.05). No relationship between virulence and biochemical characteristics was observed.  相似文献   

13.
Highly virulent strains (HVS) of Xanthomonas axonopodis pathovar (pv.) malvacearum (Xam) infect all commercial cultivars of cotton, including the long-established “immune” cultivar 101-102B. Here, we present high-quality draft sequences of a highly virulent Xam strain (GSPB2388) from Sudan, and a strain of race 18 (GSPB1386) from Nicaragua, using Illumina/Solexa paired-end sequencing. The short sequence reads were assembled into 61 scaffolds for GSPB2388 (N50 of 164 kb) and 127 scaffolds for GSPB1386 (N50 of 100 kb), with draft maps of roughly 5 Mb, which contain 4,665 and 4,520 protein-coding genes, respectively. Through gene annotation and comparisons with plant pathogen proteins, 181 and 178 potential virulence-related genes, including genes encoding a major group of type III effectors, were identified from GSPB2388 and GSPB1386, respectively. The differential effectors and sequence diversity between the HVS and race 18 may enable the identification of key factors that contribute to the high virulence of HVS. Additionally, the average nucleotide identity (ANI) between Xam and Xanthomonas axonopodis pv. citri is 98.4 %, suggesting that these strains belong to the same species.  相似文献   

14.
辛菌胺对15种植物病原菌的离体抗菌活性研究   总被引：1，自引：0，他引：1  
分别采用菌丝生长速率法和吸光度法测定了辛菌胺对10种植物病原真菌和5种植物病原细菌的离体抗菌活性,结果表明辛菌胺具有广谱的抗菌活性,其中在真菌方面对番茄叶霉病菌的活性最高,EC50N4．3180μg／mL,对其他几种真菌的活性相对较低,但EC∞均〈100μg／mL;辛菌胺对细菌均表现出较高的抑制活性,其中对棉花角斑病菌的活性最高,EC50为0．1749μg／mL,对另外4种细菌的EC50值也均〈5μg／mL。  相似文献   

15.
O'Garro  Gore  & Ferguson 《Plant pathology》1999,48(5):588-594
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.  相似文献   

16.
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.  相似文献   

17.
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.  相似文献   

18.
 为了揭示过氧化氢酶基因katExoo在水稻白叶枯病菌(Xanthomonasoryzaepv.oryzae,Xoo)过氧化氢(H2O2)抗性和致病性中的功能,本研究构建了基因缺失突变体ΔkatExoo,测定了突变体的H2O2抗性、过氧化氢酶(CAT)活性、在离体培养条件下的生长速率以及对水稻的致病性。用标记基因置换法获得了ΔkatExoo突变体,其保守的CAT结构域(GATase1_catalase和catalase_clade_2)被GmR片段所替换。katExoo基因缺失突变并不导致病菌的H2O2抗性和CAT活性降低或丧失,反而在一定程度上使之增强和升高。ΔkatExoo离体生长量显著降低,水稻接种叶片病斑明显缩短、在叶组织内的种群量下降。表明基因缺失突变显著地影响了病菌的生长、定殖和致病性。本研究结果为“KatExoo可能是Xoo的一个毒性因子”的假设提供了遗传学证据。  相似文献   

19.
ABSTRACT The highly virulent African strains of Xanthomonas campestris pv. malvacearum are quarantined pathogens in the United States and can evade or overcome all commercially utilized resistance (R) genes in cotton grown in the United States including the entire set of host differential lines used to distinguish 19 races of the pathogen. Nevertheless, the African strains carry multiple DNA fragments that strongly hybridize with members of the Xanthomonas avirulence (avr)/pathogenicity (pth) gene family. Since all previously tested members of the gene family confer avirulence against one or more R genes in cotton, strains carrying multiple members might not be expected to evade so many different R genes. The hybridizing DNA fragments were cloned from African strain XcmN and found to confer water-soaking ability to a nearly asymptomatic mutant strain of the pathogen. Restriction mapping, Southern hybridization, and DNA sequencing of the cloned fragments from XcmN were used to identify two water-soaking genes, pthN and pthN2, as new members of the Xanthomonas avr/pth gene family. The complete DNA sequence of pthN was obtained, and it is >94% identical with all other sequenced members of the gene family. Gene fusions of pthN with avrb6 (another family member) and other experiments revealed that the ability of African strain XcmN to water-soak cotton and avoid recognition by commercially used cotton R genes is determined by the specific repeats of multiple functional members of the Xanthomonas avr/pth gene family.  相似文献   

20.
ABSTRACT A technique was developed to inoculate uniformly and gently the internal phyllosphere from the upper surface of cotton leaves with the phytopathogenic bacterium Xanthomonas campestris pv. malvacearum. The inoculum consisted of 2 to 3 x 10(7) CFU/ml in CaCO(3)-saturated sterile distilled water containing 0.02%, vol/vol, of the wetting agent Silwet L-77. A custom-made inoculation apparatus was employed to immerse a circular area of the adaxial surface of a leaf in inoculum for 90 s. This resulted in uniform, passive entry of bacteria into the substomatal chambers, producing an endophytic bacterial population of 2 x 10(4) CFU/cm(2). Microscopic signs of infection were visible 48 to 72 h after inoculation. In susceptible leaves, uniformly distributed water-soaked spots were observed 7 to 8 days after inoculation. When the technique was used on resistant leaves, the autofluorescence that is characteristic of hypersensitively necrotic cells developed in the guard cells and palisade cells lining substomatal chambers, but not in the underlying spongy mesophyll.  相似文献   

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