Bacteria - Westcott's Plant Disease - page 41

A general classification of plant pathogenic
prokaryotes is shown below:
Kingdom: Prokaryotae - Organisms with genetic
material not organized into a nucleus that is
not surrounded by a membrane.
Bacteria: Have a cell membrane and cell wall.

Part III: Irregular, Gram-positive, nonsporing
rods.
F AMILY : Mycobacteriaceae -The plant pathogens
formerly classified into the genus Corynebacte-
rium were separated into the genera:
Clavibacter, Curtobacterium, Rhodococcus,
Anthrobacter, and Rathoyibacter. Bacteria in
all genera are pleomorphic rods and form yel-
low colonies that are slow growing. Separation
of the genera is based primarily on the presence
of specific amino acids in the cell walls. Posi-
tive identification of the genera is very difficult.
G ENUS : Clavibacter. Contains important phyto-
pathogenic bacteria

Part I: Gram-negative aerobic rods and cocci.
F AMILY : Pseudomonadaceae
G ENUS : Pseudomonas, rod-shaped, one or several
polar flagella, colonies white.
Xanthomonas, rod-shaped, one polar flagel-
lum, colonies yellow.
Xylella, rod-shaped, under some cultural con-
ditions filamentous; nonmotile, aflagellate,
nonpigmented.
Burkholderia, rod-shaped bacteria, motile by
one or more polar flagella, colonies white,
nutrition very versatile.
Acidovorax, rod-shaped bacteria, motile by sin-
gle polar flagellum, colonies white, limited
number of sugars are used for growth.
Rhizomonas, small rod-shaped bacteria,
motile by single polar flagellum, colonies
slow growing and white, causes corky root
of lettuce.
Rhizobacter, rod-shaped bacterium with one
lateral or polar flagellum, colonies white to
yellowish-white

formerly classified as

Corynebacterium.

Part IV: Actinomycetes, bacteria forming

branching filaments.
F AMILY : Streptomycetaceae
G ENUS : Streptomyces. Gram-positive, aerial myce-
lium with chains of nonmotile condidia.

Part V: Mollicutes, prokaryotes that have a cell
membrane but no cell wall.
F AMILY : Mycoplasmataceae, the plant

mycoplasmalike organismsphytoplasmas.

Spiroplasmataceae.
G ENUS : Spiroplasma, helical, motile but lacking
flagella. Phytoplasma, pleomorphic cells not
culturable in artificial medium.
The taxonomy of the plant pathogenic fastid-
ious phloem-limited bacteria is still unknown,
and the taxonomy of the phytoplasmas, and
of the spiroplasmas is tentative. Furthermore,
Richettsialike organisms (RLOs) have been
reported to be associated with a number of
plant diseases. RLOs are also cultured with diffi-
culty which is a characteristic similar to the
phytoplasmas. On this basis, both phytoplasmas
and RLOs are referred to as 'fastidious prokary-
otes'. There are more than 200 distinct plant
diseases affecting several hundred genera of
plants which have been shown to be caused by
the Mollicutes.
The taxonomic scheme for mollicutes and
phytoplasmas is difficult to present in this hand-
book since morphological criteria are limited and
both the criteria used in bacteriology and the

depending upon the

medium, causes carrot bacterial gall.
Ralstonia, rod-shaped bacterium with single
polar flagellum, colonies white and usually
pleomorphic in shape, causes bacterial wilt
in over 200 species of plants.
Xylophilus, rod-shaped bacterium with single
polar flagellum, colonies yellow and slow-
growing, causes cankers on grape vines.
F AMILY : Rhizobiaceae
GENUS : Agrobacterium, rod-shaped sparse lateral
flagella, colonies white, rarely yellow.

Part II: Gram-negative facultative anaerobic
rods.
F AMILY : Enterobacteriaceae
G ENUS : Erwinia, peritrichous flagella, colonies
white or yellow.
Pantoea, peritrichous flagella, colonies yel-
low. Nutritionally restricted.