Fastidous Bacteria

The Mollicutes
phytopathogenic bacteria invade their host plants through:

ral openings or wounds, colonizing intercellular spaces, expressing virulence fa
nducing various host plant responses.
w, however, are introduced directly into the sugar-rich phloem sieve tubes or int
r-transporting xylem elements by vascular-feeding
vascular insects.
vascular-colonizing bacteria can be divided into three groups:

.wall-less mollicutes (phytoplasmas and spiroplasmas),
spiroplasmas
.walled phloem-inhabiting bacteria, and walled xylem-limited bacteria.
The Mollicutes: Phytoplasmas and Spiroplasmas
Biology
toplasmas, spiroplasmas,, mycoplasmas and their relatives, all prokaryotes lacking

walls and sharing other unusual cytological and molecular features, together make
he class Mollicutes ("molli" - soft; "cute" - skin).
group comprises the smallest and simplest self-replicating

self cellular organisms,
1.2 µm in diameter and having correspondingly small genomes (18-
ing from 0.3-1.2
daltons).
Characteristics of Mollicutes
mollicutes share several unique features:

ck a rigid envelope and are bounded only by a plasmalemma they are pleomor
eir morphology is influenced by their environment,
hey are osmotically fragile, and they resist antibiotics, such as penicillin, that targe
all formation.
ycoplasmas and spiroplasmas, but not phytoplasmas, are cultivable on artificial m
t their recalcitrance to cultivation and the requirement for sterols and other un
gredients in the growth medium of many of them has led to their descriptio
astidious."
plasmas (Family Spiroplasmataceae)
Spiroplasmataceae are usually helical in morphology
suring 0.08 - 0.2 µm wide and 2-4 µm long. Plant pathogenic species may
helicity when in their insect vector. Motility includes translational movemen
ding taxes based on gradients of chemicals, temperatures and othe
onmental factors), rotation about a central axis and a bending/tumbling
on.
corn stunt disease

Dissemination of Mollicutes
t pathogenic mollicutes are transmitted by leafhoppers, planthoppers or

ids (Class Insecta:: Order Hemiptera: Suborder Homoptera). These small
cts feed by inserting straw-like
like stylets into mesophyll, xylem, or phloem
es of a suitable plant host.
oplasmas and phytoplasmas have a propagative relationship with their

ors . After being taken up by the feeding insect during phloem ingestion they
e into the body cavity via the midgut region of the intestine.
Fastidious Bacteria
(Phyloem colonizing)
llows" type symptoms (foliar chlorosis, stunting, unthriftiness and death) and also sufferin
oem necrosis, visible as a darkened ring in freshly cut stem sections, are incited by walled
cteria.
em-resident
resident walled bacteria are generally very small bacilli that generally possess Gram-
Gram
ative prokaryotic cell morphology.
outer membranes of some are wavy or rippled in appearance, a feature that gave rise to th
y name "Rickettsia-like organism" or RLO.
y a few of the phloem-resident
resident bacterial plant pathogens have been placed taxonomically, a
e fall into the phylum Proteobacteria. Candidatus Liberobacter asiaticum and Candidatus L
anum,, causal agents of the very serious citrus greening disease in Asia and Africa,
ectively.
Fastidious Xylem-Limited
Limited Bacteria (XLB)
led bacterial pathogens also inhabit the water-transporting

water cells of the xylem of
plants and are transmitted by xylem feeding sharpshooters and spittlebugs, membe
eafhopper family.
e assumed to be viruses, these bacteria were later designated "fastidious" because o

culty of cultivation, and "rickettsia-like"
like" because of superficial similarities of
led walls with that group.
mple: Clavibacter xyli subsp. xyli (sugarcane ratoon stunting disease)

yli subsp. cynodontis (bermudagrass stunting disease)
Phanerogamic Parasites
plants which produce flower and subsequently bear seeds in fruits and parasitized
on other plants known as Phanerogamic parasite”
General Properties of Parasitic Plants
ents and water are transported via a Physiological bridge called the Haustorium.
asite connects its vascular system (at least one of the tissue) to that of the host plant.
arasite may totally discard its own photosynthesis.
ites may be mostly exposed at the surface of the host (Epiparasite).
(
y parasite hidden within the host organ (Endoparasite
Endoparasite).
ndoparasitic portion is composed of thread-like haustoria permeating the host tissue with a sinker, a
structure that becomes embedded in the host tissue.
Types of Phanerogamic Parasites
•Stem
Stem Parasite
•Root
Root Parasite
Stem Parasite
oparasite: Entirely Dependent

Example: Dodder on gardens, ornamentals and hedge plants.
mi-Parasite: Partially Dependent

Example: Loranthuson fruits, wasteland, roadside and forest trees.
Root Parasite
oparasite: Entirely Dependent
For Example: Orobanche on tobacco, mustard, Brinjal tomato, cabba

flower, turnip and many other solanaceous and cruciferous plants.
mi-Parasite: Partially Dependent
For Example: Striga on Sugarcane, Cereals, maize and Millets.

Mechanism
• The haustoria penetrate the stem or leaf and reach into the cortical region just outside the
pericycle (tissues between endodermis and phloem)
phloem like an adventitious root.
• The haustoria secrete enzymes into the plant tissues that hydrolyze reserved food stuffs, such
as starch and thus make them available to the dodder plant.
• These hydrolyzed substances and water are absorbed by the haustoria and are transported to
the dodder stem where they are utilized for further growth and reproduction.
Virus
uses are tiny, non-cellular
cellular infectious organisms that can only multiply within a host cell. Viruses canno
classed as either living or non-living
living organisms from a biological standpoint. However, they have som
tinctive characteristics of living and non-living
living elements. Viroids are smaller than viruses and have
cular strings of ribonucleic acids (RNA) with no protein covering. Viroids are known to only infect plan
Nature of Virus
microscopic
rcellular
nsmissible
igate parasite
Characters of Virus
y nucleo-capsid
leic acid either DNA or RNA
•Double or single stranded (ssDNA & RNA, dsDNA & RNA)
king cell organelles
No cell membrane
No ribosomes
No cytoplasm
n pass through bacterial filter
Morphology of Virus
d shaped
Rigid and flexible rod shaped
•E.g.: TMV and PVX
yhedral: Many sides

•E.g. TNSV, wound tumor virus
illiform: Five time longer than width

•Rhabdovirus
mini virus: Twin coat

•Cotton leaf curl virus
Composition of Virus
leic acid: 5-40%
tein: 95 – 60 %
id (rare cases)

Fastidous Bacteria

Uploaded by

Copyright:

Available Formats

Fastidous Bacteria

Uploaded by

Document Information

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Fastidous Bacteria

Uploaded by

Copyright:

Available Formats

The Mollicutes

phytopathogenic bacteria invade their host plants through:

vascular-colonizing bacteria can be divided into three groups:

toplasmas, spiroplasmas,, mycoplasmas and their relatives, all prokaryotes lacking

group comprises the smallest and simplest self-replicating

mollicutes share several unique features:

corn stunt disease

t pathogenic mollicutes are transmitted by leafhoppers, planthoppers or

oplasmas and phytoplasmas have a propagative relationship with their

led bacterial pathogens also inhabit the water-transporting

e assumed to be viruses, these bacteria were later designated "fastidious" because o

mple: Clavibacter xyli subsp. xyli (sugarcane ratoon stunting disease)

General Properties of Parasitic Plants

oparasite: Entirely Dependent

mi-Parasite: Partially Dependent

oparasite: Entirely Dependent

For Example: Orobanche on tobacco, mustard, Brinjal tomato, cabba

mi-Parasite: Partially Dependent

For Example: Striga on Sugarcane, Cereals, maize and Millets.

yhedral: Many sides

illiform: Five time longer than width

mini virus: Twin coat

leic acid: 5-40%

You might also like