1. Bell Work Week of Monday, Feb. 9 – Friday, Feb. 13 Monday, Feb. 9
Describe the difference between a plant pest and a plant disease?
Bell Work

2. Plant Science AAEC – Paradise Valley Spring 2015
Plant Diseases
Plant Science
AAEC – Paradise Valley
Spring 2015

3. Plant Disease: a pathogen or the environmental factor which impacts the normal functions of the plant.
Plant diseases can be either pathogenic or nonpathogenic.
What is a plant disease?

4. What factors must be present to have a pathogenic disease?
A susceptible host.
A pathogenic organism.
Environmental conditions favorable to the pathogen.
What factors must be present to have a pathogenic disease?

5. What causes plant diseases?
Fungi
What causes plant diseases?
Example: Powdery Mildew

6. What causes plant diseases?
Bacteria
What causes plant diseases?
Example: Citrus Canker

7. What causes plant diseases?
Virus
What causes plant diseases?
Example: Tobacco Mosaic Virus

8. What causes plant diseases?
Nematodes
What causes plant diseases?
Example: Root-Knot

9. What causes plant diseases?
Environmental Conditions
What causes plant diseases?
Example: Fruit Bleaching

10. What causes plant diseases?
Fungi
Bacteria
Viruses
Nematodes
Environmental conditions

11. Plant Disease - Fungi

12. What are the two types of fungi?
There are two types of fungi:
Beneficial (saprophyte)
Disease-causing (parasites).
What are the two types of fungi?
Saprophytes: feed on organic waste (put nutrients back into the soil)
Parasites: feed on the host (rob nutrients from the host organism)

13. Fungi – Plant Infestations
They reproduce by forming spores, sclerotia, and Mycelia fragments. In order for infection to occur, the spores must germinate and penetrate the plant tissue by one of three methods:
Direct penetration
Penetration through stomata
Penetration through wounds
Fungi – Plant Infestations

14. What factors are necessary for fungal infection?
Moisture
Temperature
Stage of plant growth
Disseminating agents
Duration of spore release
What factors are necessary for fungal infection?

15. Life Cycle of a Plant Disease
Inoculation
Reproduction
Dissemination
Penetration
Infection
Incubation
Invasion

16. Example Life Cycle: Peach Brown Rot

17. Plant Disease - Bacteria

18. Diseases caused by bacteria:
There are about 170 species of bacteria that are pathogenic to plants. All of these species are present in the United States. Most bacteria are beneficial. They increase the fertility of the soil by making nitrogen from the air available to plants. They also recycle dead plants and animals. Bacteria divide very rapidly. Under ideal conditions a single cell can divide every thirty minutes. If the resulting cells continued dividing, this single cell could produce 8,388,608 bacterial cells in only 12 hours.
Diseases caused by bacteria:

19. What conditions are necessary for bacterial growth?
Warmth
Moisture
What conditions are necessary for bacterial growth?

20. Common Bacterial Disease Symptoms
Wilt
Common Bacterial Disease Symptoms

21. Common Bacterial Disease Symptoms
Leaf Spot
Common Bacterial Disease Symptoms

22. Common Bacterial Disease Symptoms
Soft Spot
Common Bacterial Disease Symptoms

23. Common Bacterial Disease Symptoms
Gall
Common Bacterial Disease Symptoms

24. Common Bacterial Disease Symptoms
Canker
Common Bacterial Disease Symptoms

25. Common Bacterial Disease Symptoms
Wilts
Leaf spots
Soft rot
Galls
Cankers
Common Bacterial Disease Symptoms

26. How are bacteria spread?
Blowing rain
Insects
Man
Seed
How are bacteria spread?

27. Plant Disease - Virus

28. Diseases caused by viruses:
Viruses are tiny particles that are about 0.1 to 0.01 microns in size (1 micron=0.001 millimeters). Viruses do not consist of cells but of nucleic acid (RNA or DNA) surrounded by a protein sheath. Viroids are simpler than viruses, they are composed of only a strand of RNA. Viruses and viroids are inactive when they are outside of living cells. When these pathogens enter a cell, they use the cell to multiply themselves, which upsets the cell=s metabolism and causes disease.
Diseases caused by viruses:

29. Are viruses sometimes helpful?
Yes, viruses were orignially used to give plants mottled color (such as Rembrandt tulips) and to produce dwarf cultivars.
Are viruses sometimes helpful?
***Original Rembrandt tulips are no longer sold commercially due to the damage the viruses cause to the bulbs.***

30. What are some common symptoms of viruses?
Mosaic: causes green leaves or fruit to become mottled.
What are some common symptoms of viruses?

31. What are some common symptoms of viruses?
Rosetting: short bushy growth caused by some viruses.
What are some common symptoms of viruses?

32. What are some common symptoms of viruses?
Ring spot viruses: show up as pale or yellow spots on leaves.
What are some common symptoms of viruses?

33. What are some common symptoms of viruses?
Leaf curling: deformed leaves.
What are some common symptoms of viruses?

34. What are some common symptoms of viruses?
Mosaic: causes green leaves or fruit to become mottled.
Rosetting: short bushy growth caused by some viruses.
Ring spot viruses: show up as pale or yellow spots on leaves.
Leaf curling: deformed leaves.
What are some common symptoms of viruses?

35. Tobacco: most tobacco contains viruses, a person who uses tobacco can spread viruses.
Insects: some viruses incubate inside insects and later injected into plants.
Seed: A few viruses are seed borne. Southern peas are a good example.
How are viruses spread?

36. Bell Work Week of Monday, Feb. 9 – Friday, Feb. 13 Tuesday, Feb. 10
Describe 3 factors which must be present for a pathogenic disease to spread.
Bell Work

37. General Disease Diagnosis

38. What are symptoms and signs?
A symptom is a plant’s response to a disease causing organism or condition.
Example: wilt or leaf spot.
A sign is the disease-causing organism itself or its products.
Example: fusiform rust spores.
What are symptoms and signs?

39. What are the steps in diagnosing a disease?
Identify the plant.
Observe symptoms and signs.
If you know what diseases are common in the area, decide if the symptoms are typical of common problems.
If the disease is not common, refer to a handbook.
If you are familiar with the symptoms, and know what is causing the problem, you do not need to make a pinpoint diagnosis.
Keep in mind that symptoms can change and secondary symptoms may mask the original problem. Ex. With most root diseases, secondary symptoms are what we see.
If you have a serious disease that you cannot diagnose, seek help from resources such as the Cooperative Extension Service.
What are the steps in diagnosing a disease?

40. What are some ways to keep diseases away from healthy plants?
Choose clean seeds.
Select clean plants.
Quarantine new arrivals.
Choose resistant varieties.
What are some ways to keep diseases away from healthy plants?

41. How are diseases controlled?
Cultivation
Mulch
Deep plowing
Sanitation
Crop rotation
Resistant varieties
Chemicals
Biological
How are diseases controlled?

42. What are some examples of famous plant disease outbreaks?
Chestnut Blight--U.S. Potato Blight--Ireland
What are some examples of famous plant disease outbreaks?

43. American Chestnut Blight

44. Summary Questions What is a diseased plant?
What factors must be present to have a pathogenic disease?
Name 3 causes of disease in plants.
What factors are necessary for fungal infection?
What is the life cycle of a disease?
What are some common bacterial disease symptoms?
How are bacteria spread?
What are some ways to keep diseases away from healthy plants?
How are diseases controlled?
Summary Questions