This document discusses the causes of plant diseases, categorizing them as biotic (living) or abiotic (non-living). Biotic causes include fungi, bacteria, viruses, viroids, algae, nematodes, and phanerogamic parasites. Fungi are the largest pathogen group and reproduce sexually and asexually. Bacteria are prokaryotic and enter plants through openings or wounds. Viruses have RNA or DNA genomes and are transmitted by vectors. Nematodes are roundworms that can be ecto- or endoparasitic. Abiotic causes are not associated with pathogens and can be due to environmental factors like drought or flooding. Koch's postulates provide a framework for proving
4.
It includes eukaryotic ,prokaryotic .
Its mesobiotic agents like virus and
viroids.
LIVING /BIOTIC
AGENTS
5.
These are diseases with which no animate
or virus pathogen is associated.
Since no parasite is associated with these
diseases they are also known as non-
parasitic diseases.
Abiotic disorders can be caused by natural
processes,suchas drought, frost, snow and
hail; flooding and poor drainage.
ABIOTIC /NON
LIVING
7. FUNGI
•Largest pathogen group.
•More than 8OOO pthogenic sp.
•Most phytopathogenic fungi belong to
the Ascomycetes and the Basidiomycetes.
•Its eukaryotic,spore
bearing,achlorophyllous,cell wall chitin
/cellulose.
• fungi reproduce
both sexually and asexually via the
production of spores and other structures.
8.
9. *
*Bacteria is prokaryotes ,unicelluar,motile,non
motile,microscopic organisms .
*Its smallar then fungi ,lacks chlorophyll,reproduce
asexually by binary fission.
*Most bacteria that are associated with plants are
actually saprotrophic and do no harm to the plant
itself.
*Bacterial diseases are much more prevalent
in subtropical and tropical regions of the world.
*Most plant pathogenic bacteria are rod-shaped
(bacilli).
*The bacteria enter the plant through natural
openings, like the stomata of the leaves, or
through wounds in the plant tissue.
11. There are many types of plant virus, and
some are even asymptomatic. Under normal
circumstances, plant viruses cause only a loss
of crop yield. Therefore, it is not
economically viable to try to control them,
the exception being when they
infect perennial species, such as fruit trees.
Most plant viruses have small, single-
stranded RNA genomes. However some plant
viruses also have double stranded RNA or
single or double stranded DNAgenomes.
Viruses, viroids and virus-like organisms
12.
These genomes may encode only three or
four proteins: a replicase, a coat protein,
a movement protein, in order to allow cell to
cell movement through plasmodesmata, and
sometimes a protein that allows transmission
by a vector. Plant viruses can have several
more proteins and employ many different
molecular translation methods.
Plant viruses are generally transmitted from
plant to plant by a vector, but mechanical and
seed transmission also occur. Vector
transmission is often by an insect (for
example, aphids).
14. *
*Spiroplasma are wall less prokaryotes which
lack riged cell wall but bounded by unit
membrane .
*Shape is spiral to helical shape
*Sensitive to tetracycline and resistance to
penicillin.
*Theycan be culture on artificial media
*Requiring cholesterol for their growth.
*Grame negative.
15. ALGAE
• Algae are eukaryotic,ubiquitous organism
,ubiquitous organisms.
• Cell wall is thick and riged and uni or
multicelluar.
• They reproduced by both sexually and
asexually .
• Disease is called Red rust
16. Phanerogamic parasites are flowering plants ,
which are capable of parasitize the crop plants by
drawing nutrition and water.
Semi (or )
partial
Holo (or )
total
Partial stem parasite – loranthus
Partial root parasite – striga
Total stem parasite–
cuscuta
Total root parasite–orabanche
17. NEMATODES
Nematods are bilaterlly symmetric,free
living organism .
Its ubiquitous and resembling round
worms.
Ectoparasitic or endoparasitic
.migratory or sedentary.
They are a problem in tropical
and subtropical regions of the world.
Nematodes are able to cause radical
changes in root cells in order to
facilitate their lifestyle.
18.
19.
20. KOCH POSTULATES
ROBERT KOCH(1882)
The pathogen must be show constant association with
the disease.
The pathogen must be isolated from the diseased host
and grown in pure culture.
The Pathogen from the artificial culture should be
able to reproduce the disease when inoculated on
healthy plant of the same kind. The symptoms
produced should be identical with those seen on the
plant from which isolation was made.
Artifically produced diseasedshould yield the same
pathogen on reisolation
