Xanthomonas

4 Key excerpts on "Xanthomonas"

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  eBook - PDF

  Genetics of Bacterial Diversity

  • David A. Hopwood, Keith F. Chater(Authors)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  The remaining three genera, Agrobacterium (the subject of Chapter 18), Pseudomonas and Xanthomonas are members of the family Pseudomonadaceae and have been studied extensively. The examples given in this chapter will be drawn mostly from research on Xanthomonas campestris, the subject of investigations in the author's laboratory, but much of what follows applies to other xanthomonads and pseudomonads. A discussion of the taxonomy of these organisms is inappropriate here, but certain points of nomenclature are important because they describe the specificity of the pathogens for their hosts. Members of the genus Xanthomonas, which consists exclusively of plant pathogens, are yellow-pigmented, motile, aerobic, Gram-negative rods. Five species are currently recognized, of which one, X. campestris, is divided into about 120 pathovars, defined as groups distinguishable from one another with certainty only by plant host range. Typically a given pathovar can infect only a small number of closely-related plant species. Pathovars are often further divided into races which show specificity for certain genotypes or cultivars of a single plant species. Pseudomonas syringae also provides examples of subspecific division into pathovars and races. X. campestris pathovar campestris (hereafter X. c. campestris) causes black rot of crucifers (1), one of the most serious diseases of brassica crops worldwide (Fig. 1). Infection of a crop usually begins with contaminated seed. As the seedling 17. Pathogenicity o/Xanthomonas 355 Figure 1. Black rot symptoms produced by X.c. campestris about two weeks after inoculation via small wounds at the leaf margins. The bacteria migrate inwards through the vascular system and as the populations increase at each point the characteristic progression of symptoms of chlorosis (chlorophyll destruction), vein blackening (deposition of melanin-like pigments) and rotting is seen.

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  eBook - PDF

  Genetics of Bacterial Diversity

  • David A. Hopwood, Keith F. Chater(Authors)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  A discussion of the taxonomy of these organisms is inappropriate here, but certain points of nomenclature are important because they describe the specificity of the pathogens for their hosts. Members of the genus Xanthomonas, which consists exclusively of plant pathogens, are yellow-pigmented, motile, aerobic, Gram-negative rods. Five species are currently recognized, of which one, X. campestris, is divided into about 120 pathovars, defined as groups distinguishable from one another with certainty only by plant host range. Typically a given pathovar can infect only a small number of closely-related plant species. Pathovars are often further divided into races which show specificity for certain genotypes or cultivars of a single plant species. Pseudomonas syringae also provides examples of subspecific division into pathovars and races. X. campestris pathovar campestris (hereafter X. c. campestris) causes black rot of crucifers (1), one of the most serious diseases of brassica crops worldwide (Fig. 1). Infection of a crop usually begins with contaminated seed. As the seedling 17. Pathogenicity o/Xanthomonas 355 Figure 1. Black rot symptoms produced by X.c. campestris about two weeks after inoculation via small wounds at the leaf margins. The bacteria migrate inwards through the vascular system and as the populations increase at each point the characteristic progression of symptoms of chlorosis (chlorophyll destruction), vein blackening (deposition of melanin-like pigments) and rotting is seen. The photograph also shows the effect of humidity on disease symptoms; the leaf on the left was maintained at low ambient humidity while that on the right was covered with a plastic bag to give high humidity. 356 M.J. Daniels emerges and grows the bacteria colonize the surface of the plant.

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  Sustainable Approaches to Controlling Plant Pathogenic Bacteria

  • V. Rajesh Kannan, Kubilay Kurtulus Bastas(Authors)
  • 2015(Publication Date)
  • CRC Press

    (Publisher)

  The immense diversity of plant pathogens, which include viruses, bacteria, fungi, nematodes, and insects, approximates 7100 species. Among these, roughly 150 are bacterial species that cause diseases to plants. The major ways that bacterial pathogens cause plant diseases are by obtaining nutrients one or more host plants for their own growth; using specific mechanisms to secrete proteins and other molecules to locations on, in, and near their hosts; and by exploiting these proteins and other molecules modulate or avoid plant defense circuitry to enable parasitic colonization (Chisholm et al., 2006; Davis et al., 2008). Bacterial plant diseases are most frequent and severe in tropical and subtropical places, where warm and humid conditions are ideal for bacterial growth. Indeed, consistent annual crop losses are recorded in all countries.

  The problem of plant diseases, particularly in developing countries, is aggravated by the paucity of resources devoted to pathological studies. This gap in the literature may be the result of an inability to quantify plant diseases, followed closely by an inability to relate information about plant diseases to the failure of crops to reach manageable yields. In general, plant pathogenic bacterial species belonging to Xanthomonadaceae, Pseudomonadaceae, and Enterobacteriaceae families target all types of plants that can supply them with appropriate food and shelter. The most devastating plant pathogens belong to genera such as Erwinia , Pectobacterium , Pantoea , Agrobacterium , Pseudomonas , Ralstonia , Burkholderia , Acidovorax , Xanthomonas , Clavibacter , Streptomyces , Xylella , Spiroplasma , and Phytoplasma .

  1.2 Pathogenesis of Plant Pathogenic Bacteria

  Plant bacterial diseases are generally characterized by plant morphological symptoms such as leaf and fruit spots, cankers, blights, vascular wilts, rots, and tumors. Phytopathogenic bacteria provoke diseases in plants by penetrating into host tissues (Buonaurio, 2008). Microbial pathogenicity has often been defined as the biochemical mechanisms whereby pathogenic microorganisms cause disease in a host organism (Fuchs, 1998). Microbial virulence is defined as the degree or measure of pathogenicity shown by one or more plants. Pathogenicity and/or virulence of Gram-negative plant pathogenic bacteria are strictly dependent on the presence of secretion apparatuses in host cells, through which they secrete proteins or nucleoproteins involved in their virulence within the apoplast or inject these substances into host cells (Buonaurio, 2008).

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  Plant Disease Management

  Principles and Practices

  • Hriday Chaube(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  Phytopathology, 77, 1987. With permission.)

  Plant pathogenic bacteria are non-motile or motile by means of one or more flagella (Figure 6 ), Bacterial flagella are made up of flagellin molecules. On the basis of the number and position of flagella the bacteria can be grouped in five categories. They are atrichous —no flagellum present; monotrichous —a single flagellum at one end of the cell; amphitrichous —one flagellum at each end of the cell; lophotrichous —two or more flagella at one or both ends of the cell, and peritrichous —large number of flagella all over the cell.

  ii. Reproduction

  Bacteria multiply with astonishing rapidity and their significance as pathogens stems particularly from the fact that they can produce tremendous numbers of cell in a short period of time. Rod-shaped plant pathogenic bacteria reproduce by the asexual process known as "binary fission". This is a very quick process and is completed in 20 to 30 min. At this rate one bacterial cell could produce 1 million bacteria in 6 to 10 h. Fission involves formation of a septum and chromosome division. Both the events occur simultaneously. The cells are divided by a simple division into two halves. Each half becomes an independent individual.

  iii. Classification

  The kingdom-Prokaryoteae comprised two divisions: Photobacteria and Scotobacteria. The following is the condensed form of the grouping which lists only the parts having plant pathogenic bacteria.21

  Kingdom: Prokaryoteae Division I: Photobacteria—sensitive to light, no plant pathogens Division II: Scotobacteria—indifferent to light Class I: The Bacteria — Parts 2 to 6, 9 to 14, and 16 have no plant pathogens

  Part 7: Gram-negative, aerobic rods and cocci. Five families with 14 genera and 6 genera of uncertain affiliation. Plant pathogens in the families—Family: Pseudomonadaceae (order Psudomonadales); Genera: Pseudomonas, Xanthomonas, Xylella 22

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