Pathology

Question 1

Define plant disease.

Answer 1

Any condition that changes a plant from a normal, healthy state in its form, structure, function or usefulness is defined in a broad sense as a disease.

Question 2

Define plant pathology.

Answer 2

• The study of plant diseases,
• what causes them,
• what factors influence their development and spread, and
• how to prevent or control them.

Question 3

What is a plant disease causal agent?

Answer 3

Fungal diseases, bacterial diseases, viral diseases, nematode diseases, nutrient deficiencies and similar diseases

Question 4

Disease classification by affected plant part include…

Answer 4

… root diseases, stem diseases, leaf

diseases, flower diseases or fruit diseases.

Question 5

Disease classification by symptoms include…

Answer 5

… blights, mildews, wilts, leaf spots, mosaics, trunk rots, fruit rots and many others.

Question 6

The name given to a specific plant disease generally includes three significant informational items. They are…

Answer 6

(1) The plant attacked
(2) The plant part affected
(3) How it is affected
Example,
(1) tomato (2) blossom end (3) rot,
(1) ivy (2) leaf (3) spot

Question 7

Plant pathologists divide diseases into two general categories. They are:

Answer 7

(1) Biotic diseases

(2) Abiotic Diseases

Question 8

Biotic diseases are…

Answer 8

… diseases caused by living organisms.

Question 9

Abiotic diseases are…

Answer 9

… physiological disorders caused by unfavorable weather, mechanical damage, nutrient deficiencies, excess salts, toxic chemicals or other environmental conditions.

Question 10

Biotic disease-causing organism include:

Answer 10

1. Fungi and Fungal-like organisms,
2. Bacteria,
3. Viruses,
4. Phytoplasmas,
5. Nematodes,
6. Parasitic Seed Plants

Question 11

Define Disease Symptoms.

Answer 11

Disease symptoms are the visual reaction of the plant to a biotic or pathogenic organism or to an abiotic condition. Symptoms include wilting, yellowing, abnormal swelling, plant tissue death or necrosis, stunted growth and die-back. Symptoms show plant response to the disease, but usually do not indicate the cause of the disease.

Question 12

Define Disease Signs.

Answer 12

Signs are actual evidence that enables the identification of the specific organism that infected the plant.

Question 13

What is the normal response to a plant that has been infected with a pathogenic disease?

Answer 13

Remove the plant and get it off the property to prevent infection of other plants.

Question 14

A plant “disease” is not a substance. What is it?

Answer 14

It is a process which results in damage to the plant when a specific pathogen interacts with a host plant.

Question 15

Plant disease development depends on what factors?

Answer 15

(1) the host plant’s susceptibility,
(2) the pathogen, and
(3) the environment

Question 16

What role does environment play in plant disease?

Answer 16

Environment affects a host plant’s susceptibility by creating stress in the plant due to unfavorable conditions (heat, excess water, lack of water, etc.), or, (2) it affects the pathogen by providing conditions favorable to the pathogen (moisture & temperature).

Question 17

What are the phases of plant disease development?

Answer 17

(1) Inoculation (contact of pathogen to host)
(2) Incubation (development or initial growth)
(3) Penetration (getting into the host)
(4) Infection (extraction of water & nutrients)
(5) Disease (symptoms: blight, wilt, etc.)

Question 18

Overall, what is the most important factor in UTAH to avoid plant disease?

Answer 18

Water. Since Utah is dry, managing irrigation practices. Keep the plants dry enough to hinder or stop the incubation process.

Question 19

How can cultural controls hinder the development of plant disease?

Answer 19

1. Removing waste and fallen fruit or leaves.
2. Keeping plants healthy.
3. Planting at the correct time.
4. Choosing resistant varieties.
5. Crop rotation.

Question 20

What are biological controls?

Answer 20

The use of antagonistic microorganisms to discourage or reduce harmful pathogens.

Question 21

What are chemical controls?

Answer 21

Chemical controls are commonly referred to as “fungicides.” More correctly,
• fungicides control fungi,
• bactericides control bacteria and
• nematicides control nematodes.
There are no chemical virus controls (viricides) available at present.

Question 22

What are the 3 modes of action for fungicides?

Answer 22

1. Protectants (prevent spore germination)
2. Systemic (absorbed into plant & kills fungi when it tries to enter the plant tissues)
3. Eradicants (kill the fungi after it has already entered into plant tissue.

Question 23

What is the Damage Threshold Level?

Answer 23

The lowest pest population that causes damage.

Question 24

What is “Damping Off”?

Answer 24

A seedling disease where the stem decays at the soil line after emergence or as seed decay.

Question 25

What is “Fungus”?

Answer 25

A small, many-celled microorganism without A small, many-celled microorganism without chlorophyll.

Question 26

What are “Nematodes”?

Answer 26

Generally microscopic, unsegmented roundworms that live free in moist soil, water, or decaying matter, or as parasites of plants, insects or other organisms.

Question 27

What are the two (2) main environments related to plant disease?

Answer 27

1. Atmospheric, and

2. Soil.

Question 28

What is the most prevalent biotic agent in plant What is the most prevalent biotic agent in plant disease?

Answer 28

1. Fungi (8k varieties with 80k diseases)
2. Nematodes (1k diseases)
3. Viruses/Viroids (500 diseases)
4. Bacteria (200 diseases)
5. Phytoplasms (75 diseases)

Question 29

What is the difference between a virus and a viroid?

Answer 29

A virus has both DNA and RNA and a chemical shell.

A viroid has only RNA and no shell. Smaller than a virus.

Question 30

Name three (3) requirements to ensure the best use of a chemical applications.

Answer 30

1. Time of application (before infection… preventative only)
2. Method of application (proper dilution)
3. Selection of chemical agent