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.     

Molecular typing of Japanese strains of Ralstonia solanacearum in relation to the ability to induce a hypersensitive reaction in tobacco

The genetic diversity of 120 Ralstonia solanacearum strains isolated from a variety of host plants across Japan was assessed on the basis of hypersensitive response (HR) in tobacco leaves and phylogenetic analyses of endoglucanase gene egl, hrpB, and gyrB. Phylogenetic analysis of egl revealed that only three strains belonged to phylotype IV, and 117 strains belonged to phylotype I. Partial sequences of HrpB were identical among phylotype I strains except for one strain. Analyses using the partial nucleotide sequences of the gyrB and egl gene fragments grouped phylotype I strains into 11 gyrB and 8 egl types, respectively, whereas analyses using the partial amino acid sequences of GyrB and Egl grouped phylotype I strains into 4 GyrB and 5 Egl types, respectively. Using multilocus sequence typing of GyrB and Egl, we identified 10 unique sequence types within the Japanese phylotype I strains. Strains belonging to the GyrB42 or GyrB66 type caused wilt in tobacco, and strains belonging to GyrB2 or GyrB9 type elicited HR, demonstrating that HR induction in tobacco is genetically differentiated in the Japanese strains of R. solanacearum.     

Genetic Diversity of Xylella fastidiosa Strains from Costa Rica, São Paulo, Brazil, and United States

ABSTRACT The diversity of 42 Xylella fastidiosa strains from Costa Rica, S?o Paulo, Brazil, and the United States were analyzed using the sequence of the 16S rRNA gene by variable number of tandem repeat (VNTR) fragment analysis and by restriction fragment length polymorphisms (RFLP) of a specific polymerase chain reaction (PCR)-amplification product using enzyme CfoI. Limited variability in the sequence of the 16S rRNA gene was observed and, although the separation was not absolute, most strains from Costa Rica clustered with strains from the United States and not with strains from S?o Paulo. The PCR-RFLP produced different patterns of DNA bands. The same pattern was shared by strains from Costa Rica, the United States, and two coffee strains from S?o Paulo, but a different pattern was observed in six coffee and orange strains from Brazil. In all, 32 amplification products were scored in the VNTR fragment analysis. The total variation observed among the X. fastidiosa strains had significant (P < 0.001) contributions from both geography and host origin as inferred by Nei's values of genetic diversity and WINAMOVA statistics. The strains from Costa Rica were isolated from diseased grapevines, coffee, and sweet orange and these strains grouped together and could be distinguished from strains from grapevine from the United States or from either coffee or sweet orange from S?o Paulo. The strains tested from Costa Rica are most likely of local origin, although the possibility that they have been introduced along with horticultural crops cannot be excluded. In either case, they are examples of independent selection of strains of X. fastidiosa affecting coffee and sweet orange. Greater genetic similarity was observed between strains from Costa Rica and the United States than with those from S?o Paulo.     

Geographical Genetic Structure of Xylella fastidiosa from Citrus in São Paulo State, Brazil

ABSTRACT A total of 360 Xylella fastidiosa strains were isolated from sweet orange (Citrus sinensis) cv. Pera plants growing in five geographic regions in the Brazilian state of S?o Paulo. The genetic variation of these strains was determined by 15 variable number tandem repeat (VNTR) and 58 random amplified polymorphic DNA (RAPD) markers. The mean values of genetic diversity (H) of X. fastidiosa strains within each geographic region determined by RAPD (H(RAPD)) were substantially lower than H(VNTR) values. H(RAPD) values ranged from 0.00 to 0.095, whereas the H(VNTR) values ranged from 0.024 to 0.285. A highly significant value of Nei's coefficient of gene differentiation (G(ST) = 0.355; P = 0.000) was detected among all five populations. Analysis of the molecular variance (AMOVA) also revealed significant genetic differentiation among regions or populations ( phi(STAT) = 0.810; P< 0.001). In addition, genetic differentiation among subpopulations (plants) within the regions (phi(STAT) = 0.699; P < 0.001) and within each plant (phi(STAT) = 368; P < 0.001) were statistically significant. These high values of genetic differentiation among X. fastidiosa strains from different regions suggest a genetic structure according to region of host origin. However, no apparent correlation between genetic distance and region of origin of populations were supported statistically by Mantel analysis (r = 0.27; P = 0.22).     

Genetic variability of Iranian strains of Pseudomonas syringae pv. syringae causing bacterial canker disease of stone fruits

Strains of Pseudomonas syringae pv. syringae (Pss) were isolated from healthy and diseased stone fruits tissues sampled from 38 stone fruits orchard sites in Iran in 2010 and 2011. These strains were tested for pathogenicity and the presence of the syrB gene and were genetically characterized by using ERIC (enterobacterial repetitive intergenic consensus), REP (repetitive extragenic palindromes), and BOXAIR and IS50 (insertion sequences) primers and PCR. All 78 strains of Pss tested were moderately to highly pathogenic on Loring peach seedlings. A total of 78 isolates of the Pss amplified a 752-bp fragment with the syrB primers. To assess genetic diversity among the strains, genomic DNA was extracted from strains and used in rep-PCR and IS50-PCR analysis. Cluster analysis was performed using UPGMA. The strains of Pss were separated into nine distinguishable genotypic groups by the combination data set of both rep-PCR and IS50-PCR at 73 % similarity level. There was no significant correlation between genetic diversity and geographical origin of the isolates. These results indicate that a combination of rep-PCR and IS50-PCR fingerprinting can be used as a high resolution genomic fingerprinting method for elucidating intrapathovar diversity among strains of Pss. The results of this study demonstrated the existence of a considerable genetic diversity among Pss strains causing canker of stone fruit trees in Iran. In this study, genetic variability in Iranian strains of Pss were established, which will be of immense use in the development of resistant genotypes against this bacterial pathogen.     

Characterization of Clavibacter michiganensis subsp. michiganensis strains from recent outbreaks of bacterial wilt and canker in Serbia

Sixty-eight Clavibacter michiganensis subsp. michiganensis (Cmm) strains from recent outbreaks of bacterial wilt and canker in Serbia were collected from several tomato growing regions during a three-year period. The pathogen was identified based on bacteriological characteristics and pathogenicity tests and the identity of strains was confirmed by DAS ELISA and PCR amplification using primers CMM5/6 and PSA4/R. The strains showed homogeneity in biochemical and physiological properties. However, pathogenicity tests revealed differences in virulence that are presumably due to a loss of the pat-1 gene. Further strain characterization using DNA-based methods revealed a high diversity of the Serbian Cmm strains. Based on multi-locus sequence typing (MLST) analyses of five genes, Cmm strains were divided into seven groups. The pulsed-field gel electrophoresis (PFGE) pattern of a selection of strains supported the groupings based on trees of the kdpA/sdhA sequences. On the other hand, groupings made according to PFGE and MLST were not correlated to plasmid content in all cases. This study suggested that high genetic variability of the Serbian Cmm strains was detected both in MLST and PFGE analyses, and could have resulted either from new Cmm strains being introduced by seeds from different origins or as a consequence of an intraspecific hybridization process. In addition, this study proposed MLST as an efficient tool in epidemiological studies, population biology investigations and tracking the routes of transmission of pathogens. Four of the five house-keeping genes (kdpA, sdhA, ligA and gyrB) selected to characterize Cmm strains proved to be suitable for the MLST analysis. This is the first study carried out on the characterization of Cmm using MLST.     

Geographic substructure of Fusarium asiaticum isolates collected from barley in China

Fusarium head blight (FHB) can affect wheat and barley and is a devastating disease caused by a complex of Fusarium species. Here we report on a large-scale survey on the genetic diversity of isolates collected from barley in China. Ten VNTR markers were tested on a representative set of 40 isolates covering 14 sampling areas along the Yangtze River. VNTR4 and VNTR7, with 13 and 6 alleles, each were applied to a total of 1106 single-spore isolates to reveal the population structure of F. asiaticum. The F. asiaticum population showed high genetic diversity and a clear genotypic substructure within China. Pair-wise comparisons of allele frequencies between the mountainous provinces of Sichuan and Chongqing in Western China, Hubei Province in the centre or the eastern provinces of Zhejiang, Jiangsu and Shanghai showed significant differences. Even between counties of the same province, significant differences between allele frequencies were found (P?<?0.001). Our results indicate serious constraints for migration of this pathogen in the major cereal-growing areas of China.     

Genetic diversity analysis of Acidovorax citrulli in China

Acidovorax citrulli has become quite common in China. A collection of 118 strains of A. citrulli was made from throughout China and other countries to determine their genetic relatedness. Strains were identified as A. citrulli by pathogenicity, phenotypic characterization, and PCR. Genetic diversity was determined using pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). PFGE electrophoresis resulted in nine genotypes, which could be typed into two groups based on host; group 1 included strains mainly from melon and group 2 included strains mainly from watermelon. MLST analysis resulted in 73 sequence types (ST) among the 118 A. citrulli strains. All A. citrulli strains were typed into three groups: group 1 with 82 strains (including type strain Fc247), group 2 with 35 strains and group 3 a singleton (Fc380). Similar to PFGE results, group 1 included strains mainly from melon and group 2 included strains mainly from watermelon. The difference was the 10 watermelon strains (pslbtw1-3, 5–11) from Beijing grouped with melon strains of group 1 based on MLST, suggesting that these 10 watermelon strains had a close relationship with melon. Our study indicated that there was genetic differentiation among A. citrulli strains between watermelon and melon. Also, our study was the first attempt to compare PFGE and MLST on analyzing genetic diversity of A. citrulli strains and proved MLST could better distinguish A. citrulli strains.     

Characterization and differentiation of soft rot causing Pectobacterium carotovorum of Indian origin

Twenty different strains of Pectobacterium carotovorum (Pcc) were recovered from vegetable-growing fields of Vadodara, Gujarat (India) using a plant host enrichment approach during the years 2006–9. The isolated strains, based on differences in physiological and biochemical features, were classified into five different biovars, and then identified as Pectobacterium carotovorum (Pcc) by species-specific PCR and 16S rDNA sequences. Moreover, these Pcc strains were also differentiated based on virulence traits, plant cell wall degrading enzymes production and phylogenetic analysis of 16S rDNA sequence and Repetitive extragenic palindromic—PCR (rep-PCR). High genetic variability, independent of their pathogenicity, was revealed among these Pcc strains by rep-PCR typing using four different primer sets . Factors other than the plant host specificity seem to correlate with genetic variability of these economically important Pcc strains. Significantly, polyphasic characterization of the Pcc strains clearly reveals the heterogeneity among them. The present studies can be considered as useful epidemiological surveillance (or distribution) of soft rot causing Pcc in the semi arid region of India.     

基于全基因序列的中国北方3省(区)马铃薯Y病毒遗传多样性分析

本研究以马铃薯Y病毒(PVY)全基因组为基础,分析吉林、黑龙江和内蒙古3省(区)PVY群体遗传多样性和群体分化,并评估突变、重组、选择等遗传力所起的作用。根据已报道的PVY全基因序列保守区设计4对引物,采用片段重叠法对来自内蒙古和吉林的24个PVY分离物全基因序列进行测定,并联合NCBI中已登录的9个黑龙江分离物全基因组序列进行遗传多样性参数评估、群体分化检验和分子变异等分析。结果显示,我国北方3省(区)PVY群体遗传多样性高,其中内蒙古和黑龙江PVY群体遗传多样性高于吉林群体,并且3个群体之间呈现一定程度的遗传分化。分子变异分析发现在PVY基因组中存在1 786个变异位点,表明我国北方3省(区)PVY群体变异程度较高,并且这种高变异度有85.54%来自各个马铃薯种植区内PVY个体的遗传变异。重组分析和系统发育分析发现,我国北方3省(区)PVY群体中重组株系占比高达90.3%,并具有明显的株系多样性,表明PVY重组株系已成为我国北方3省(区)马铃薯种植区的流行株系。选择压力分析显示,使用FEL和IFEL法分别检测出501个和315个净化压力选择位点,这表明3省(区)PVY群体受净化选择压力为主。以上结果表明,中国北方3省(区)PVY群体遗传多样性高,突变、重组和自然选择都对遗传多样性和群体分化存在一定影响。     

福建及贵州等地烟草青枯菌系统发育分析

[目的]探寻烟草上青枯菌的系统发育.[方法]采用演化型分类框架对福建及贵州等地的62个烟草青枯病菌株进行鉴定分析.[结果]基于内切葡聚糖酶基因系统发育学的分析结果表明:所有参试菌株均归属于青枯菌亚洲分支的4个序列变种,分别为序列变种15、17、34和44;尚未发现归属于美洲或非洲分支的烟草青枯病菌株.其中序列变种15和17为优势菌系,序列变种34的菌株都来自福建省,只发现3个菌株属于序列变种44.基于avrA基因的氨基酸序列比对结果表明4个序列变种的avrA基因都属于RS1000类型.[结论]本研究表明福建及贵州等地烟草上的青枯菌存在一定的遗传分化.     

Biochemical genetics of oxidative resistance to diazinon in the house fly

The genetics and biochemistry of oxidative resistance to diazinon were investigated in a diazinon-resistant strain of the house fly, Musca domestica L. The resistant strain was crossed with a multimarker susceptible strain and substrains containing portions of the resistant strain genome were prepared. Resistance, microsomal oxidase, and cytochrome P-450 spectral characteristics were then compared in the different strains. The major gene for resistance to diazinon is semidominant and is located on chromosome II, 13 crossing over units from the recessive mutant stubby wing. Additional resistance genes occur on chromosome II and on other chromosomes as well. Resistance to diazinon was introduced into a susceptible mutant-marked strain via genetic crossing over. Increases in parathion oxidase, total and P-450-specific N- and O-demethylase activity, and resistant strain type I binding spectrum were introduced along with resistance, indicating genes controlling these parameters and resistance are either identical or closely linked. No increase in activity of cytochrome P-450 itself was introduced into the mutant strain. Additional genes controlling the amount of cytochrome P-450 and several spectral changes characteristic of the resistant strains are apparently controlled by genes located at different loci on chromosome II. Resistance factors on other chromosomes are also present, but were not characterized.     

Characterization of Pectobacterium carotovorum subsp. carotovorum and brasiliense from diseased potatoes in Kenya

Using a DNA-based typing method, 48 bacterial strains isolated from infected potato (Solanum tuberosum) tubers originating from Kenya were characterized. The pel gene specific primers showed that all the 48 bacterial strains were pectolytic. Subspecies-specific primers EXPCCF/EXPCCR and Br1f/L1r identified 66 % of the strains as Pectobacterium carotovorum subsp. carotovorum while 34 % were identified as Pectobacterium carotovorum subsp. brasiliense based on their characteristic band sizes of 550 and 322 bp, respectively. Amplification of the 16S-23S rDNA (ITS) region did not yield observable differences in banding patterns between the Kenyan strains. However, PCR-RFLP analysis together with partial nucleotide sequences of the housekeeping mdh and gapA genes confirmed the results obtained by the specific primers. Phylogenetic analysis of the concatenated partial gene sequences grouped Pectobacterium carotovorum subsp. carotovorum and Pectobacterium carotovorum subsp. brasiliense Kenyan strains together with those identified in other parts of the world with 90 % and 99 % bootstrap support values, respectively. Pathogenicity assays using representative Kenyan strains demonstrated varied levels of tuber maceration ability. The Pectobacterium carotovorum subsp. carotovorum and Pectobacterium carotovorum subsp. brasiliense Kenyan strains were shown to be less aggressive in causing soft rot when compared to type strains. This study describes for the first time the genetic diversity of pectolytic bacteria causing soft rot disease of potatoes in Kenya.     

Potato bacterial wilt in India caused by strains of phylotype I, II and IV of Ralstonia solanacearum

Bacterial wilt or brown rot is one of the most devastating diseases of potato caused by a bacterium Ralstonia solanacearum (Smith 1986) Yabuuchi et al. (Microbiol Immunol 39:897–904 1995). Traditionally, R. solanacearum is classified into five races (r) on the basis of differences in host range and six biovars (bvs) on the basis of biochemical properties. Recently using molecular methods, R.?solanacearum has been classified into phylotypes based on the intergenic transcribed sequence of the ribosomal RNA genes 16S and 23S and into sequevars based on the endoglucanase gene (egl) sequence. In the present study, 75 bacterial strains, isolated from wilt infected potatoes from various potato growing regions of India, were classified by traditional and molecular methods. The identity of all the strains was confirmed as R. solanacearum as expected single 280-bp fragment resulted in all the strains following PCR amplification using R. solanacearum specific universal primer pair 759/760. Biovar (bv) analysis, based on utilization of disaccharide sugars and hexose alcohols, categorised the 75 strains into bv2 (78.7 %), 2 T (5.3 %), 3 (5.3 %) and 4 (10.7 %). The phylotype specific multiplex PCR assigned 78.7 % strains to phylotype II, 16.0 % to phylotype I and 5.3 % to phylotype IV. Phylogenetic analysis of egl gene sequences clustered all fifty nine phylotype II (bv2) strains with reference strain IPO1609 (IIB-1), all four phylotype IV (bv2T) strains with reference strain MAFF301558 (IV-8), three phylotype I (bv3) strains with reference strain MAFF211479 (I-30) and all eight phylotype I (bv4) and one phylotype I (bv3) strain with reference strain CIP365 (I-45). The study concluded that the Indian potato strains of R. solanacearum belong to three out of four phylotypes namely: the Asian phylotype I, the American phylotype II, and the Indonesian phylotype IV. This is the first study to address the diversity of R. solanacearum from potato in India using phylotype and sequevar scheme. We also report here for the first time the occurrence of phylotype IV sequevar 8 (bv2T) strain of R. solanacearum causing potato bacterial wilt in mid hills of Meghalaya in India.     

Genetic diversity of Spiroplasma citri strains from different regions, hosts, and isolation dates

Spiroplasma citri, a phloem-limited pathogen, causes citrus stubborn disease (CSD). Losses due to CSD in California orchards have grown over the past decade. To investigate the possibility of introduction or emergence of a new strain, a study of genetic diversity among S. citri strains from various locations was conducted using random amplified polymorphism DNA-polymerase chain reaction (RAPD-PCR) of 35 strains cultured from 1980 to 1993, and of 35 strains cultured from 2005 to 2006. Analysis using 20 primer pairs revealed considerable diversity among strains. However, no unique genetic signatures were associated with recently collected strains compared with those collected 15 to 28 years ago, and no geographically associated pattern was distinguishable. S. citri strains from carrot and daikon radish contain some unique DNA fragments, suggesting some host plant influence. Multiple strains from single trees also showed genetic diversity. Sequencing of five RAPD bands that differed among strains showed that diversity-related gene sequences include virus fragments, and fragments potentially encoding a membrane lipoprotein, a DNA modification enzyme, and a mobilization element. No differences in colony morphology were observed among the strains. The lack of correlation between PCR patterns and isolation date or collection site is inconsistent with the hypothesis that recent infections are due to the introduction or emergence of novel pathogen strains.     

Genetic variability within <Emphasis Type="Italic">Septoria carvi</Emphasis> Syd.- a pathogen of caraway <Emphasis Type="Italic">Carum carvi</Emphasis> L

Genetic variability within Septoria carvi isolates obtained from various organs of caraway cultivated in south-eastern and central Poland was studied using the RAPD-PCR technique. The tests were performed using randomly selected primers. The DNA profiles obtained using four primers proved useful in determining genetic variability among the genotypes of Septoria carvi isolates. The present study characterized the differences in the nucleotide sequence within the internal transcribed spacer region of rDNA (ITS1, 5.8S, ITS2) of selected S. carvi isolates and reference strains of Septoria spp. Moreover, eight isolates were sequenced for three loci: actin, calmodulin and translation elongation factor 1-alpha, and the obtained sequences were compared with the sequences of Septoria reference strains affecting other plants of the family Apiaceae. Phylogenetic analysis showed distinct differences of the tested isolates, which allowed to treat them Septoria carvi species affecting the above-ground organs of caraway Carum carvi L. This study is the first report on the genetic characteristics of the species S. carvi.     

Evaluation of the Genetic Diversity of Xylella fastidiosa Strains from Citrus and Coffee Hosts by Single-Nucleotide Polymorphism Markers

ABSTRACT The aim of this study was to obtain information about genetic diversity and make some inferences about the relationship of 27 strains of Xylella fastidiosa from different hosts and distinct geographical areas. Single-nucleotide polymorphism (SNP) molecular markers were identified in DNA sequences from 16 distinct regions of the genome of 24 strains of X. fastidiosa from coffee and citrus plants. Among the Brazilian strains, coffee-dependent strains have a greater number of SNPs (10 to 24 SNPs) than the citrus-based strains (2 to 12 SNPs); all the strains were compared with the sequenced strain 9a5c. The identified SNP markers were able to distinguish, for the first time, strains from citrus plants and coffee and showed that strains from coffee present higher genetic diversity than the others. These markers also have proven to be efficient for discriminating strains from the same host obtained from different geographic regions. X. fastidiosa, the causal agent of citrus variegated chlorosis, possesses genetic diversity, and the SNP markers were highly efficient for discriminating genetically close organisms.     

甘薯病毒G CH株系和CH2株系中国分离物基因组全序列克隆及结构特征分析

为明确甘薯病毒G(sweet potato virus G,SPVG)CH株系中国分离物SPVG-CH-Ch1和CH2株系中国分离物SPVG-CH2-Ch1的基因组结构特征及遗传变异情况,利用RT-PCR和RACE方法克隆获得分离物SPVG-CH-Ch1和SPVG-CH2-Ch1的基因组全序列,应用DNAMAN软件对基因组全序列及不同编码区序列进行分子变异分析,并基于多聚蛋白基因序列利用MEGA 7软件进行系统进化分析。结果表明,分离物SPVG-CH-Ch1和SPVG-CH2-Ch1的基因组分别包含10 813个和10 834个核苷酸,均包含1个开放阅读框,由10 467个核苷酸组成,编码含有3 488个氨基酸残基的多聚蛋白。分离物SPVG-CH-Ch1与SPVG-CH2-Ch1之间的基因组全序列核苷酸一致性为78.6%,二者与GenBank中登录的其它SPVG分离物基因组全序列核苷酸一致性分别为78.6%～99.1%和77.9%～98.6%,其中SPVG-CH-Ch1与IS103分离物(KM014815)的核苷酸一致性最高,为99.1%,与WT325分离物(KF790759)的核苷酸一致性最低,为78.6%;SPVG-CH2-Ch1与WT325分离物的核苷酸一致性最高,为98.6%,与66Al分离(KX279878)的核苷酸一致性最低,为77.9%。系统进化树显示,SPVG-CH-Ch1与CH株系的7个分离物形成1个分支,SPVG-CH2-Ch1与CH2株系的WT325分离物形成1个分支。表明SPVG的CH株系和CH2株系之间的变异较大,株系内较保守。     

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.     

油菜菌核病生防芽孢杆菌的分离鉴定及其脂肽化合物分析

采用平板拮抗筛选,分别从西藏日喀则地区和拉萨地区杂草根围土壤中筛选到2个对油菜菌核病菌有显著拮抗活性的芽孢杆菌菌株RJGP16和YBWC43。通过生理生化鉴定、16S rDNA序列分析和BOX-PCR指纹图谱分析,鉴定菌株RJGP16为萎缩芽孢杆菌Bacillus atrophaeus, 菌株YBWC43为解淀粉芽孢杆菌Bacillus amyloliquefaciens。离体叶片试验结果显示,菌株RJGP16和YBWC43对油菜菌核病菌防治效果分别为50.24%和100.00%。脂肽化合物种类分析显示,菌株RJGP16产生脂肽化合物表面活性素和芬枯草菌素,菌株YBWC43产生杆菌霉素D和芬枯草菌素。表明菌株RJGP16和YBWC43对油菜菌核病的防治效果与其产生的脂肽化合物有关。