Whole Genome Sequences of Nine Xanthomonas Strains Responsible for Common Bacterial Blight of Bean.

We report the complete and circularized genome sequences of nine strains of Xanthomonas phaseoli pv. phaseoli and Xanthomonas citri pv. fuscans, which cause common bacterial blight of bean. These assemblies provide high-quality material for functional and evolutionary studies of these legume pathogens.

Rapid Detection of Xanthomonas citri pv. fuscans and Xanthomonas phaseoli pv. phaseoli in Common Bean by Loop-Mediated Isothermal Amplification.

A single loop-mediated isothermal amplification (LAMP) assay was developed for specific detection of both pathogens that cause bacterial blight in common bean, Xanthomonas phaseoli pv. phaseoli (Xpp) and Xanthomonas citri pv. fuscans (Xcf). The objective was to provide a simple, easy-to-use, specific, and sensitive method to investigate the presence of one or both pathogens in plant material and seeds for routine diagnosis. The detection limits for both pathogens were 10 CFU/ml for cell suspensions and 1 fg of DNA, whereas in conventional PCR, the primers detected up to 105 CFU/ml and 1 ng of DNA. Specificity was confirmed by testing DNA from bean leaves, other Xanthomonas species, common fungal and bacterial bean pathogens, and bacteria from the leaf microbiota. The method was tested with bean leaves inoculated with Xpp, and the pathogen could be detected from 4 h up to 15 days postinoculation, even before disease symptoms were visible. When the method was applied to bacterium detection (Xpp or Xcf) in seed lots from infected plants, the bacterium detection rate was 100% (24 of 24). The pathogens were detected in seeds incubated for just 1 h in saline solution (0.85%), reducing the time needed for bacterium detection. The LAMP assay could be useful as a tool in bean bacterial blight management. Rapid and sensitive detection of bacteria in bean seed lots would reduce the risks of planting highly contaminated seeds in environments favorable to blight multiplication.

Xanthomonas citri pv. viticola Affecting Grapevine in Brazil: Emergence of a Successful Monomorphic Pathogen.

The pathovar viticola of Xanthomonas citri causes bacterial canker of grapevine. This disease was first recorded in India in 1972, and later in Brazil in 1998, where its distribution is currently restricted to the northeastern region. A multilocus sequence analysis (MLSA) based on seven housekeeping genes and a multilocus variable number of tandem repeat analysis (MLVA) with eight loci were performed in order to assess the genetic relatedness among strains from India and Brazil. Strains isolated in India from three related pathovars affecting Vitaceae species and pathogenic strains isolated from Amaranthus sp. found in bacterial canker-infected vineyards in Brazil were also included. MLSA revealed lack of diversity in all seven genes and grouped grapevine and Amaranthus strains in a monophyletic group in X. citri. The VNTR (variable number of tandem repeat) typing scheme conducted on 107 strains detected 101 haplotypes. The total number of alleles per locus ranged from 5 to 12. A minimum spanning tree (MST) showed that Brazilian strains were clearly separated from Indian strains, which showed unique alleles at three loci. The two strains isolated from symptomatic Amaranthus sp. presented unique alleles at two loci. STRUCTURE analyses revealed three groups congruent with MST and a fourth group with strains from India and Brazil. Admixture among populations were observed in all groups. MST, STRUCTURE and e-BURST analyses showed that the strains collected in 1998 belong to two distinct groups, with predicted founder genotypes from two different vineyards in the same region. This suggest that one introduction of grape planting materials contaminated with genetically distinct strains took place, which was followed by pathogen adaptation. Genome sequencing of one Brazilian strain confirmed typical attributes of pathogenic xanthomonads and allowed the design of a complementary VNTR typing scheme dedicated to X. citri pv. viticola that will allow further epidemiological survey of this genetically monomorphic pathovar.

Draft Genome Sequence of Erwinia psidii, Causal Agent of Bacterial Blight of Guava (Psidium guava) and Dieback of Eucalypt (Eucalyptus spp.).

Here, we present a draft genome sequence of the type strain IBSBF 435 of Erwinia psidii (Enterobacteriaceae), a phytopathogen that causes bacterial blight on guava (Psidium guava) and dieback and wilt on eucalypt (Eucalyptus spp.), both of which are important emerging diseases.

Polyphasic Characterization of Pigmented Strains of Xanthomonas Pathogenic to Cashew Trees.

The export of cashew (Anacardium occidentale) nuts generates millions of dollars for the Brazilian economy annually. However, production may be limited by the occurrence of diseases that affect cashew trees, such as Xanthomonas spot and angular leaf spot, which are caused by pigmented strains of Xanthomonas and Xanthomonas citri pv. anacardii, respectively. Thirty-one pigmented strains of Xanthomonas were characterized for phenotypic, pathogenic, and molecular attributes. These strains were similar to X. citri pv. anacardii in phenotypical characteristics, sensitivity to antibiotics and copper compounds used in agriculture, epidemiology, and repetitive sequence-based polymerase chain reaction (rep-PCR) profiles. When inoculated into Brazilian pepper, cashew, mango, and hog plum seedlings, the pigmented strains of Xanthomonas and X. citri pv. anacardii produced similar symptoms. However, the pigmented strains of Xanthomonas were more aggressive toward cashew plants than toward the other hosts tested, which confirms their specificity. We conclude that pigmented strains of Xanthomonas are very aggressive on cashew trees and should not be considered casual pathogens of these hosts. Moreover, based on our results from rep-PCR and IS1595-PCR amplification, we suggest that these strains constitute a variant of X. citri pv. anacardii.

Low genetic diversity among pathogenic strains of Erwinia psidii from Brazil / Baixa diversidade genética entre estirpes patogênicas de Erwinia psidii no Brasil

Erwinia psidii causes bacterial disease of guava in Brazil. Phenotypic and molecular characterization through rep-PCR fingerprinting of 42 strains from different geographical regions showed that E. psidii populations in Brazil have a low level of genetic diversity and suggest that contaminated plant material is the main source for pathogen dissemination in the country.

Erwinia psidii é o agente causal da seca-dos-ponteiros ou bacteriose da goiabeira no Brasil. A caracterização fenotípica e molecular através de rep-PCR de 42 estirpes patogênicas de diferentes regiões mostrou que as populações de E. psidii no Brasil têm um baixo nível de diversidade genética e sugere que material de propagação infectado é a principal fonte de disseminação do patógeno para novas áreas no país.

Low genetic diversity among pathogenic strains of Erwinia psidii from Brazil.

Erwinia psidii causes bacterial disease of guava in Brazil. Phenotypic and molecular characterization through rep-PCR fingerprinting of 42 strains from different geographical regions showed that E. psidii populations in Brazil have a low level of genetic diversity and suggest that contaminated plant material is the main source for pathogen dissemination in the country.

Crinipellis brasiliensis, a new species based on morphological and molecular data.

Crinipellis perniciosa infects a diversity of hosts causing severe damage to T. cacao production in many Brazilian growing regions. We compared isolates of Crinipellis from different geographic origins and hosts in Brazil by structural analysis using light (LM) and scanning electronic microscopy (SEM), as well as RFLP and sequence data based on the nuclear rDNA ITS region. Statistical analyses of morphometric data of basidia and basidiospores revealed a distinct group of isolates of Crinipellis obtained from Heteropterys acutifolia when compared to representatives from Theobroma cacao, Solanum lycocarpum and Heteropterys nervosa. A similar distinction also was observed based on sequence data of the ITS region such that combined results allowed for the segregation of a new species within the genus Crinipellis.

Nuclear and mitochondrial rDNA variability in Crinipellis perniciosa from different geographic origins and hosts.

Genetic variability in Crinipellis perniciosa, the causal organism of witches' broom disease in Theobroma cacao, was determined in strains originating from T. cacao and other susceptible host species Heteropterys acutifolia and Solanum lycocarpum in Brazil, in order to clarify host specificity and geographical variability. RFLP analysis of the ribosomal DNA ITS regions (rDNA ITS), and the mitochondrial DNA small subunit ribosomal DNA gene (mtDNA SSU rDNA) did not reveal any genetic variability in 120 tested strains, possibly serving only as species level markers. Genetic variability was observed in the ribosomal DNA IGS spacer region, in terms of IGS size, RFLPs and sequence data. Phylogenetic analyses (using CLUSTAL W, PHYLIP and TREEVIEW) indicated considerable differences between C. perniciosa strains from T. cacao and those from H. acutifolia (85-86%) and S. lycocarpum (95-96%). Sequence differences also indicated that C. perniciosa from T. cacao in Bahia is less variable (98%) when compared to the pathogen on T. cacao in Amazonas (97-98%), perhaps reflecting a recent introduction to T. cacao in Bahia.