PLANT DISEASESPLANT DISEASESDr. M.I.E.BARAKATDr. M.I.E.BARAKAT

Head Department of Botany & Plant PathologyHead Department of Botany & Plant Pathology

20042004

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.

• 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.

• 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.

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.

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

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.

• 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.

• Plant diseases cause variable amounts of damage every year.

• Often the severity of damage depends on weather patterns.

TYPES OF DISEASES TYPES OF DISEASES

• NON-INFECTIOUS (Abiotic) : • Nutrition, • Moisture,• Temperature,• Other Meteorological Conditions, • Toxic Chemicals.

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

DISEASE DEVELOPMENT DISEASE DEVELOPMENT

• WHAT DOES IT TAKE TO PRODUCE DISEASE?

• Three factors interact to produce disease - The Host, - The Pathogen, - and The environment

INFECTION BY PATHOGENSINFECTION BY PATHOGENS

DISEASE SYMPTOMSDISEASE SYMPTOMS

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

• 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)

Symptoms on storage organsSymptoms on storage organs

• Storage organs include tubers, bulbs, and corms.

• 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.)

• 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).

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).

Pythium

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)

- 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).

Stem, branch, and trunk Stem, 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)

• - 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).

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)

http://plant-disease.ippc.orst.edu/image.cfm?RecordID=260

Fire blight Damage to Young FruitFire blight Damage to Young Fruit

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).

HOW DISEASES ARE MANAGED HOW DISEASES ARE MANAGED

• QUARANTINE • SEED CERTIFICATION • ERADICATION CROP ROTATION ERADICATE ALTERNATE HOSTS SANITATION

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

FUNGICIDESFUNGICIDES

• Protectant Fungicides• Systemic fungicides

THE ENDTHE END