The broadest definition of plant disease includes anything that damages plant health. This definition can include such diverse factors as pathogens, insufficient nitrogen, air pollution, lawnmower damage, and deer damage.

1. PLANT DISEASESPLANT DISEASES
Dr. M.I.E.BARAKATDr. M.I.E.BARAKAT
Head Department of Botany & Plant PathologyHead Department of Botany & Plant Pathology
20042004

2. WHAT IS A PLANT DISEASE?WHAT IS A PLANT DISEASE?
• The broadest definition of plant disease
includes anything that damages plant
health. This definition can include such
diverse factors as pathogens, insufficient
nitrogen, air pollution, lawnmower
damage, and deer damage.

3. • A stricter definition usually includes any
persistent irritation resulting in plant
damage and characteristic symptoms.
This definition includes such factors as
pathogens, insufficient nitrogen, and air
pollution.. However, it excludes factors
such as lawnmower injury to trees and
lightning injury since this damage
presumably is a one-time occurrence.

4. • A very strict definition includes only
infectious organisms (pathogens) that
multiply and spread to other nearby plants.
Most pathogens are microscopic and
include bacteria, fungi, nematodes,
viruses, mollicutes, protozoa, and parasitic
plants. These are called biotic diseases.
Plant pathologists usually do not consider
organisms such as insects, deer, rodents,
and birds to be pathogens.

5. WHAT IS PLANT PATHOLOGY?WHAT IS PLANT PATHOLOGY?
• Plant pathology strives to increase our
knowledge about plant diseases, as a science.
• To do this, Plant pathologists study such factors
as
• the biology of the pathogenic organisms,
• the mechanisms that pathogens use to cause
disease,
• and interactions between pathogens and host
plants.

6. • These studies help plant pathologists to
devise better methods of preventing or
controlling diseases and alleviating the
damage that they cause.

7. PLANT DISEASES IN HISTORYPLANT DISEASES IN HISTORY
• Phytophthora late blight which caused the
potato famine in Ireland (1845- 1846).
• Hundreds of thousands of people died,
• Approximately one and a half million
people immigrated to the United States.

8. • Downy mildew of grape almost ruined the
French wine industry in the late 1800's.
The success of Bordeaux mixture in
controlling this disease gave great
encouragement to agriculturists and
stimulated the study of the nature and
control of plant diseases.

9. • Plant diseases cause variable amounts of
damage every year.
• Often the severity of damage depends on
weather patterns.

11. TYPES OF DISEASESTYPES OF DISEASES
• NON-INFECTIOUS (Abiotic) :
• Nutrition,
• Moisture,
• Temperature,
• Other Meteorological Conditions,
• Toxic Chemicals.

12. INFECTIOUS (Biotic)INFECTIOUS (Biotic)
• Fungi
• Bacteria
• Viruses & viroids
• Phytoplasmas
• Nematodes
• Parasitic plants

17. DISEASE DEVELOPMENTDISEASE DEVELOPMENT
• WHAT DOES IT TAKE TO PRODUCE
DISEASE?
• Three factors interact to produce disease
- The Host,
- The Pathogen,
- and The environment

19. INFECTION BY PATHOGENSINFECTION BY PATHOGENS

21. DISEASE SYMPTOMSDISEASE SYMPTOMS
• Root symptoms
-Injury to the root system often includes
+Yellowing,
+Stunting,
+Knot or galls
+or wilting of above-ground parts.

22. • Wash off the roots when possible and look for
the following:
- Small discolored or dead areas (fungi).
- General death of the feeder roots or the entire
root system (fungi).
- Discoloration of the vascular tissue in the
crown and lower stem (fungi, such as Verticillium
spp. and Fusarium spp., bacteria).
-Galls on roots (crown gall (caused by bacterium
Agrobacterium tumefaciens, fungal diseases
such as club rot of cabbage, root knot
nematodes)

27. Symptoms on storage organsSymptoms on storage organs
• Storage organs include tubers, bulbs, and
corms.

28. • Symptoms on these organs include:
Discolored or dead areas that go deep
into storage organs (fungi, bacteria)
- Dry rots (fungi).
- Soft rots accompanied by strong,
repulsive odors (bacterial pathogens, such
as Erwinia spp.) (Frequently, bacterial soft
rots move into tissue originally attacked by
pathogenic fungi, making diagnosis of the
original pathogen difficult.)

29. • Scabby lesions on potato skins (bacteria
such as common scab) .
- Galls on storage organs (fungi,
nematodes).
- Internal problems (several viruses or
bacteria, such as ring rot of potato).

36. Seedling diseasesSeedling diseases
• - Seedlings fail to emerge,
or fall over and die
(damping-off caused by fungi such as
Rhizoctonia, Pythium, and Fusarium)
- Dead areas on cotyledons or stems
(fungi, bacteria).

37. Pythium

39. Leaf symptomsLeaf symptoms
- Leaf discoloration or yellowing in
localized or distinct patterns (viral).
- Necrotic (dead) areas on leaves, often
containing fruiting bodies (fungi)
- Necrotic areas on leaves, often with
water-soaked margins (bacterial)
- Small rusty-red, brown or black spots
and stripes (fruiting bodies of rusts and
smut fungi)

40. - Leaf distortion (elongated, dwarfed,
thickened, etc.) (viral).
- Leaf galls (fungi such as peach leaf curl
and oak leaf blister, insects).
- - White, powdery substance on leaves
(powdery or downy mildew).
- - Wilting (vascular wilt fungi, root rot
pathogens, bacteria, drought).

47. Stem, branch, and trunkStem, branch, and trunk
disordersdisorders
• - Cankers and complete or partial death of
woody stems or branches (fungi and bacteria)
• - Sticky ooze from trunks and branches
(bacteria, mechanical injury, stress, boring
insects, sapsuckers (birds))
• - Large conks and bracket-like fruiting structures
on trunks and branches (wood-rotting fungi)

53. • - Galls or swellings on lower trunk and/or
branches (crown gall bacterium, white
pine blister rust)
• - Witches' brooms or excessive branching
(fungi, mistletoes, phytoplasmas).
• - Extreme distortion, enlargement, and
flattening of stems or branches
(physiological/genetic condition known as
fasciation).

54. Flower symptomsFlower symptoms
• - Odd color changes (often in a mosaic pattern)
and/or distortion (viruses).
• - Death of flower parts (fungi such as gray mold
(Botrytis spp., bacteria)
• - Individual flowers or seeds converted into
masses of black spores (corn smut).
• - Flowers that are green and smaller and more
dense than normal (phytoplasma)

60. Fire blight Damage to Young FruitFire blight Damage to Young Fruit

61. Fruit symptomsFruit symptoms
• - Fruit decays, rots, and superficial spotting or
russetting (fungi). Important diagnostic
symptoms include specific color of rotted tissue,
firmness of the tissue, and signs such as spores
or fruiting structures.
• - Discolorations and malformations (viruses).
• - Discrete spots on fruit or soft rots in storage
(bacteria).

67. HOW DISEASES ARE MANAGEDHOW DISEASES ARE MANAGED
• QUARANTINE
• SEED CERTIFICATION
• ERADICATION
CROP ROTATION
ERADICATE ALTERNATE HOSTS
SANITATION

68. • HOST RESISTANCE
• PROTECTION
-CULTURAL PRACTICES
-HANDLING PRACTICES
-MANAGING INSECT VECTORS

69. FUNGICIDESFUNGICIDES
• Protectant Fungicides
• Systemic fungicides

71. THE ENDTHE END