The general characteristics of plant pathoghenic bacteria belonging to major genera has been discussed. These include: Agrobacterium, Erwinia, Pseudomonas, Xyllela e.t.c. Generally, plant pathogenic bacteria are non- spore forming, rod shaped organism. They are either gram positive or gram negative depending on their cell wall.

1. GENERAL CHARACTERISTICS OF PLANT
PATHOGENIC BACTERIA
PRESENTED BY
MUHAMMED JAKADA
CPPR 807 :PLANT BACTERIOLOGY
COURSE INSTRUCTOR: Prof. A.D Akpa
adakpa@gmail.com

2. GENERAL CHARACTERISTICS OF PLANT PATHOGENIC BACTERIA
 Majority are non-spore-forming, rod-shaped organisms.
 Only Streptomyces species form spores and are filamentous.
 They are either Gram-negative or Gram-positive depending on their
cell wall structure.
 Most are nutritionally fastidious and have growth temperature
optima around 23- 28oC.

3. GENERAL CHARACTERISTICS OF PLANT PATHOGENIC BACTERIA CONT’N
 A few pathogens, such as Ralstonia solanacearum and Burkholderia
cepacia can grow at 42oc.
 They are either strictly aerobic or facultatively anaerobic.
 They all infect hosts intercellularly.
 Genetic studies have demonstrated involvement of numerous genes in
virulence and pathogenesis.

4. MAJOR GENERA OF PLANT PATHOGENIC BACTERIA
 Agrobacterium
 Arthrobacter
 Clavibacter (Corynebacterium)
 Curtobacterium
 Erwinia
 Pseudomonas
 Rhodococcus
 Spiroplasma
 Streptomyces
 Xanthomonas
 Xylella

5. CHARACTERISTICS GENERA: AGROBACTERIUM
1. AGROBACTERIUM:
 All strains of Agrobacterium are aerobic, non-pigmented rods (0.8 by
1.5-3µm).
 They are gram negative and does not form spore.
 They are rhizosphere and soil inhabitants
 They are motile, move by means of 1-4 peritrichous flagella; when
only one flagellum is present, it is more often lateral rather than polar.
 When grown on carbohydrate-rich media, colonies are light to white
beige, convex, round, smooth, and produces abundant polysaccharide
slime

6. CHARACTERISTICS MAJOR GENERA OF PLANT PATHOGENIC BACTERIA CONT’N
 Agrobacterium spp are responsible for galling (a form of abnormal
growths, or nodules on plants).
 Many strains (A. tumefaciens) carry an indigenous plasmid (Ti
plasmid) that can transform normal plant cells into tumours cells that
proliferate to cause crown galls on plants.
 Others (A. rhizogenes) carry the Ri plasmid that initiates excessive
production of roots (hairy root disease), and many (A. radiobacter) are
nonpathogenic. (Moore et al., 1980).

7. CHARACTERISTICS GENERA: ARTHROBACTER
2. ARTHROBACTER:
 They are Gram-positive, strictly aerobic rods, showing a cycle of
development when growing on complex media.
 Some angular arrangements of cells are usually seen.
 They are non-acid-fast, catalase-positive.
 In peptone media, little or no acid is produced from glucose, gelatin is
hydrolyzed.
 Do not survive 63 oC for 30 minutes in skimmed milk.
 Bacterial blight of American holly (Ilex opaca) is induced by A. ilicis.

8. CHARACTERISTICS OF GENERA: CLAVIBACTER (CORYNEBACTERIUM)
3. CLAVIBACTER (CORYNEBACTERIUM):
 All known species of Corynebacterium are Gram-positive.
 They are non-acid fast.
 Their cells are short, straight, or slightly curved pleomorphic rods
(0.5-0.9 by 1.5-4.0 µm), slender and often club-shaped at one end.
 Sometimes they contain metachromatic granules.

9. CHARACTERISTICS OF GENERA: CLAVIBACTER (CORYNEBACTERIUM)
 The corynebacteria cause a variety of diseases including galls,
gummosis, and wilts.
 Identification is easy if suspected species are isolated from a known
host; most known species are host specific.
 They are non-branching, non-spore forming, aerobic and non-
encapsulated.
 They may be non-motile or motile (at 20 C) by means of one or two
polar flagella. They do not grow in oxidative-fermentative tests of
glucose and not acid fast (Vidaver, 1980).

10. CHARACTERISTICS OF GENERA: CURTOBACTERIUM
4. CURTOBACTERIUM :
 They are Gram-positive short rods.
 Some are pleomorphic, showing bending type of cell division.
 Older cultures show a proportion of coccoid cells, but there is no
definite rodcoccus cycle of development.
 Gram stain may be lost with age, metachromatic granules not seen.

11. CHARACTERISTICS OF GENERA: ERWINIA
5. ERWINIA:
 They are straight rods, 0.5-1.0 by 1.0-3.0 µm.
 They are mainly single and gram-negative.
 They are motile (except E. stewartii), move by means of
several to many peritrichous flagella.
 They are the only plant pathogenic bacteria that are
facultative anaerobes (Agrios, 2005), but some species
show rather weak fermentation.

12. CHARACTERISTICS OF GENERA: ERWINIA
 There are two major groups of Erwinia: the amylovora’
group and the ‘carotovora’ group.
 The ‘amylovora’ group does not produce pectic enzymes
and cause necrotic or wilt diseases.
 They produce acid from fructose, glucose, galactose and
sucrose.
 The ‘carotovora’ group has strong pectolytic activity and
cause soft rot of fleshy vegetables.

13. CHARACTERISTICS OF GENERA: ERWINIA

14. CHARACTERISTICS OF GENERA: ERWINIA
 When grown on crystal violet pectate (CVP) medium, the
soft rot Erwinia species form iridescent crosshatched
translucent colonies with deep, cup-like depressions.

15. CHARACTERISTICS OF GENERA: PSEUDOMONAS
6. PSEUDOMONAS:
• They are straight or slightly curved Gram-negative rods,
0.5-1.0 by 1.5-4.0 µm.
• They may occur singly or in chains of a few cells.
• They are motile,moves by means of one-to-many polar
flagella.
• They do not have resting structures.
• They catalase-positive, mostly oxidase positive, but some
important plant pathogens are oxidase negative

16. CHARACTERISTICS OF GENERA: PSEUDOMONAS
 They are strict aerobes, except for a few which denitrify
and thus respire anaerobically (Sands et al., 1980; Agrios,
2005).
 They are chemo-organotrophic with respiratory, never
fermentative metabolism.
 Various important plant pathogens are members of this
genus, which also contains epiphytes and saprophytes.
 Many species are common inhabitants of soil or of fresh
water and marine environments.

17. CHARACTERISTICS OF GENERA: PSEUDOMONAS
 The pseudomonads that do not produce fluorescent pigments (e.g.,
Pseudomonas solanacearum) constitute the non-fluorescent group.
 They cause numerous plant diseases with diverse symptoms, including
vascular wilts, stem cankers, soft rots, blossom and twig blights, leaf
spots, tumours or galls and even mushroom blights.

18. CHARACTERISTICS OF GENERA: RHODOCOCCUS
7. RHODOCOCCUS:
• They are gram-positive, aerobic with pleomorphic cells.
• They sometimes form mycelium that soon breaks up into irregular
elements.
• They are non-motile, non-spore forming and may be partially acid-
fast.
• Colonies are rough, smooth, mucoid or mycobacterial-like, buff, pink,
orange, red or sometimes colourless.

19. CHARACTERISTICS OF GENERA: RHODOCOCCUS
• Most strains grow well on ordinary media at 30o C, some require
thiamine.
• They reduces nitrate, but does not attack casein, elastin and
hypoxanthine.
• Acid is produced from fructose, glucose, and mannose, but not from
dulcitol, lactose, α-methylD-glucoside or raffinose.

20. CHARACTERISTICS OF GENERA: SPIROPLASMA
8. SPIROPLASMA:
• They belong to the class Mollicutes and are very small bacteria with
no cell walls but contained by their plasma membranes.
• They are pleomorphic, Gram-negative.
• They vary from helical filaments and branched non-helical filaments
to spheres and ovals.
• Helical filaments ca. 100-200 nm diameter and 3-5 µm long are
usually seen in the growth phase and may persist.

21. CHARACTERISTICS OF GENERA: SPIROPLASMA
• They are motile with flexing and twitching movement and often
appear to rotate in corkscrew fashion.
• No flagella or organelles of motion are found.
• Cells multiply by binary fission Chemo-organotrophic, facultatively
anaerobic, requiring sterols for growth.
• Acid are produced from glucose.

22. CHARACTERISTICS OF GENERA: STREPTOMYCES
9. STREPTOMYCES:
• These bacteria are soil-inhabitants, Gram-positive and have well-
developed branched, coenocytic mycelium not readily fragmenting,
0.5-2.0 µm in diameter.
• At maturity, the aerial mycelium forms chains of three to many spores,
which may be round, oval or cylindrical.
• On nutrient media, colonies are slow growing.
• They produce a wide variety of pigments that coloured the mycelium,
spores, and the substrate.
• They can grow on a variety of carbon sources and cellulose and
produce several antibiotics that act against bacteria, fungi, algae,
viruses, protozoa or tumour tissues.

23. CHARACTERISTICS OF GENERA: XANTHOMONAS
10. XANTHOMONAS:
 The cells are Gram-negative, straight rods, 0.4-1.0 by 1.2-3.0 µm
 They are aerobic, catalase positive, H2S positive, oxidase negative,
 Most xanthomonads produce yellow extracellular polysaccharide
slime, a source of ‘xanthan gum (used commercially as food additive)’
on media containing glucose.
 Colonies of these species are mucoid, convex, and shining on Yeast
extract nutrient agar (YNA) or Yeast extract-dextrose-CaCO3 agar
(YDC).

24. CHARACTERISTICS OF GENERA: XANTHOMONAS
 All Xanthomonas species are plant pathogens and are found only in
association with plants or plant material.
 All nomenspecies are regarded as members of a single taxospecies
often referred to as the X. campestris group. Young et al. (1978)
proposed that all taxospecies of X. campestris group be classified as
pathovars of X. campestris.
 The xanthomonads induce leaf spots and wilts.
 Xanthomonas are responsible for about 75% of known plant bacterial
diseases

25. CHARACTERISTICS OF GENERA: XYLELLA
11. XYLELLA:
 Cells are mostly single, straight rods, 0.3 by 1-4 µm, producing long
filamentous strands under some cultural conditions (Agrios, 2005).
 Colonies are small, with smooth or finely undulated margins.
 They are nutritionally fastidious because they require specialized
media to grow.
 They are Gram-negative, non-motile, without flagella, strictly aerobic,
non-pigmented and are inhabitants of xylem of plant tissue.

26. REFRENCES
• Agrios, G.N. (2005). Plant Pathology. Elsevier Academic Press, Fifth
Edition, 922pp.