Control of Plant Diseases - UPM EduTrain Interactive … 12.pdf · · 2014-09-19Control of Plant Diseases ... aphids & avoid spread of virus diseases of the 2 crops ... Soil treatment

Control of Plant Diseases

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Principles of Disease Control

6 principles:

1. Exclusion

2. Eradication

3. Protection

4. Resistance

5. Therapy

6. Avoidance

Application of these principles towards the 3 elements of epidemic: pathogen, host & environment


Principles of Disease Control (cont’)

1. Exclusion

To prevent the import & spread of plant pathogens into areas from which they are absent

2. Eradication

Destroy pathogens

3. Protection

Protect host plants from pathogens


Principles of Disease Control (cont’)

4. Plant resistance Pathogens fail to cause diseases

5. Therapy Treat host plants for recovery

6. Avoidance Avoid favorable environmental

conditions to pathogens


Methods of Disease Control

1. Regulatory

2. Cultural

3. Disease resistance

4. Biological

5. Physical

6. Chemical


1. Regulatory Method

i. Quarantines & inspections

Quarantine laws (local)

1. Plant Quarantine Act (1976)

2. Plant Quarantine Regulation (1981)

Inspections at all entry points

Airports, seaports, border cities

ii. Crop certification To ensure disease-free planting materials

International Standards for Phytosanitary Measures (International Plant Protection Convention, IPPC)


1. Regulatory Method (cont’)

Exotic diseases in Malaysia:

1. SALB (South American Leaf Blight) of rubber (from South America)

2. Fusarium wilt of oil palm (from Africa)

3. Witches’ broom of cocoa (from South America)

4. Cocoa swollen shoot virus of cocoa (from Africa)


2. Cultural Method

i. Sanitation Planting areas, crops,

workers, equipments, machines, storage areas, etc.

ii. Crop rotation Effective only for

controlling pathogens that survive on living plants or host residue

E.g.: Groundnut/Corn/Onion/Chilli

Source: Agrios (2005)

Pruning, bagging and removal of infected plants.


2. Cultural Method (cont’)

iii. Host eradication Destroy infected host & alternate host plants

iv. Create conditions unfavorable to the pathogen

Increase plant spacing to reduce moisture on leaf surface

Modify fertilizers or soil amendments to control soil pH

Flood fields for long periods or dry fallowing to create conditions lack of nutrients, oxygen or moisture


2. Cultural Method (cont’)

v. Maintain plant vigour

To boost resistance of host plants against pathogen infections

Proper plant spacing, fertilization, field drainage, irrigation or weed control, etc.


3. Disease Resistance

i. Non-host resistance Non-host plants are resistant to pathogens of other

plants(even under the most favorable conditions for disease development)

However, non-host plants are susceptible to their own pathogens in various degrees.

ii. True resistance Controlled by genes for resistance Also known as race-specific, cultivar-specific or

gene-for-gene resistance 2 kinds:

a. Horizontal resistanceb. Vertical resistance


3. Disease Resistance (cont’)

a. Horizontal resistance

Controlled by several genes (polygenic/multi-gene resistance)

Partial or non-race specific resistance

Non-stable resistance, affected by environmental conditions

Generally, does not protect plants from becoming infected, but slows down spread of disease

Relatively difficult to produce varieties with this kind of resistance



b. Vertical resistance Controlled by one or a

few genes (monogenic/oligogenic resistance)

Race specific resistance Stable resistance, not

affected by environmental conditions

Relatively easier to produce varieties with this kind of resistance

Brassica napus plants following inoculation with an isolate of Turnip mosaic virus. (L) Susceptible. (R) Resistant by a single dominant gene.



Horizontal and Vertical Resistance

Levels of horizontal and vertical resistance of two plant varieties toward 10 races of a pathogen. [After Vanderplank (1984).]




Development of resistant varieties

Identify the target gene

Transfer target gene to selected crop

Evaluate crop values in terms of yield, quality & resistance

Supply developed varieties to farmers


4. Biological Method

Definition

The use of other organisms to control pathogen populations

Methods used

i. Antagonistic microorganisms

ii. Trap plants

iii. Antagonistic plants

iv. Mycorrhiza (symbiotic fungus)


4. Biological Method (cont’)

i. Antagonistic microorganisms

Direct protection of plants from pathogens

Mechanisms employed:

a. Direct parasitism (causing lysis & death of pathogens)

b. Competition (for space & nutrients)

c. Production of toxins (antibiotics or volatiles, e.g., ethylene)



i. Antagonistic microorganisms (cont’)

a. Suppressive soils: Presence of antagonistic microbes such as

Trichoderma, Penicillium (fungal), or Pseudomonas, Bacillus & Streptomyces (bacteria)

b. Mycoparasites: Verticillium psalliotae (parasitized Hemileia vastatrix,

causal agent of coffee rust)

Trichoderma harzianum (parasitized Rhizoctonia,Sclerotium, Rigidoporus, Ganoderma, etc.)

c. Bacterial parasites: Bacillus penetrans (parasitized Meloidogyne javanica)


Antagonistic Microorganisms

Hyphae of Trichoderma(T) form dense coils and tightly encircle hyphae of Rhizoctonia (R).

Development of pits in the hyphal cell walls of Penicillium caused by biological agent yeast.

Meloidogyne juvenile attacked by bacterium Bacillus penetrans.

A nematode trapped by adhesive knobs produced by a fungal antagonist.




ii. Trap plants Corn planted around groundnut or chilli, help to control

aphids & avoid spread of virus diseases of the 2 crops

Crotalaria plants stimulate hatching of Meloidogyne eggs & trap its juveniles.

iii. Antagonist plants

Marigold or asparagus produce toxins, toxic to some species of parasitic nematodes in the soil

However, methods (ii) dan (iii) are seldom used due to cost.



iv. Mycorrhiza Definition:

Symbiotic fungi that infect roots but do not cause disease

Beneficial to host plants by promoting growth (improve nutrient & water intake)

Example:

Soil treatment during initial planting in the field for the control of Basal Stem Rot of oil palm(however, the treatment only improve plant vigor & ineffective in controlling spread of the disease)


mycorrhizae fungi


5. Physical Method

Methods used:

i. Heat treatment

ii. Hot-water treatment

iii. Drying

iv. Refrigeration

v. Radiation


5. Physical Method (cont’)

i. Heat treatment

a. Soil sterilization by heat

Heat produced by electricity or steam

50C: kill nematodes, some oomycetes

60C-72C: kill most fungi & bacteria

82C: kill most weeds, bacteria, viruses & insects



1. Heat treatment (cont’)b. Soil solarization

Soil covered with clear polyethylene

Leave under sun for several days or weeks

Top soil (5 cm) can reach 52 C

Kills many soilborne pathogens such fungi, nematodes & bacteria

Soil solarization reduced Fusarium wilt incidence in water melon. Blue=infested, non-solarized soils; Red= infested soil solarized for 30 days; Yellow= infested soil solarized for 60 days.




ii. Hot water treatment

Kills pathogens on surface or inside seed coats, bulb scales, etc.

Temperature & duration of treatment depend on the host-pathogen combinations

Example:

Loose smut of wheat: seeds kept in hot water at 52C, 11 min

Nematodes of bulb: bulbs kept at 43C, 3 h



iii. Drying For storage of grains, legumes, nuts & fruits

Air-dry or treated with hot air

Reduce moisture to 12% before storage

Reduce infection & decay by fungi & bacteria

iv. Refrigeration Most widely used & most effective to control

post-harvest diseases

Low temperature inhibit growth & activities of such pathogens

For the management of perishable fruits & vegetables



v. Radiation

The use of UV (ultra violet) light and (gamma) rays to kill pathogens present on fruits & vegetables

Problem with this method: dosage used may also injure plant tissues

So far, no plant diseases are controlled commercially by radiation.


Thank You


Plant disease journals

Phytopathology

Plant disease

Journal of Phytopathology

Plant pathology


reference Journal

Wetzel, T., Candresse, T., Ravelonandro, M. and Dunez, J.(1991). A polymerase chain reaction assay adapted to plum poxpotyvirus detection. Journal of Virological Methods 33, 355-365.

Books Hanold, D. (1993). Diagnostic methods applicable to viroids. In

Diagnosis of Plant Virus Diseases, pp. 295-314. Edited by R.E.F. Matthews. Boca Raton, Florida: CRC Press.

Turner, P.D. (1981). Oil Palm Diseases and Disorders, pp. 280.Kuala Lumpur: Oxford University Press.


Proceedings Vadamalai, G., Rezaian, M.A., Hanold, D. and Randles, J.W.

(2004). Ribonuclease protection assay (RPA) as a potentialtool for viroid detection. In Proceedings of the 6thAustralasian Plant Virology Workshop. Gold Coast,Queensland, Australia.

Website MPOPC (2005). Malaysian Palm Oil Promotion Council.

www.mpopc.org.my


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Control of Plant Diseases - UPM EduTrain Interactive … 12.pdf · · 2014-09-19Control of Plant Diseases ... aphids & avoid spread of virus diseases of the 2 crops ... Soil treatment