biotic disorder of crops

1. Biotic Disorders
Read Chapter 10
• At the end of this section students should be able to:
• 1) List and describe the seven major types of disease causing
organisms
• 2) Know what the most important disease causing agent is in
North America
• 3) Understand and list the classification scheme for fungi,
phyla, their characteristics and the types of diseases they
cause
• 4) Understand how fungi are spread and how the life cycles
influence which part of the fungus is most important

2. Biotic Disorders
• 5) Know and list the strategies for fungal survival in the
forest
• 6) Understand the close association between fungi and
host plant in native diseases
• 7) Describe how and why introduced diseases are so
effective at killing trees
• 8) Describe the importance of parasitic plants in the
western United States

3. Biotic Disorders
• Plant Pathology - Pathogens, Parasites,
Saprophytes, Symbiosis
– Pathogen:
– Parasite:
– Saprophyte:
– Symbiosis:
– Obligate:

4. Biotic Disorders
• Plant Pathology - Pathogens, Parasites,
Saprophytes, Symbiosis
– Facultative:
– Obligate parasite:
– Facultative parasite:
– Obligate saprophyte:
– Facultative saprophytes:

5. Disease Triangle & Tetrahedron
Host
Environment
Time

6. Disease Square

7. Biotic Disorders
• Signs and Symptoms of Disease
Signs
Symptoms

8. Biotic Disorders
• Symptoms of Disease
– Necrosis
– Decay
– Cankers
– Leaf spots
– Wilts

9. Biotic Disorders
• Symptoms of Disease
– Blights
– Hypertrophy
– Atrophy
– Physiology

11. Koch’s Postulates
Robert Koch 1843-1910
Proved Bacillus anthrax
was responsible for
disease in animals and
humans
Noble Prize Winner 1905

12. Koch’s Postulates
Proof of Pathogenicity
1) The pathogen must be associated with the disease
in all the symptomatic plants examined.
2) The pathogen must be isolated and grown in pure
culture on nutrient media and its characteristics
described.
3) The pathogen in pure culture must be inoculated
into healthy plants of the same species and produce
the same symptoms in the diseased plants in No. 1
4) The pathogen must be re-isolated from inoculated
plants and grown in pure culture again and its
characteristics must be like those described in No. 2

13. Biotic Disorders
• Types of biotic agents
– Fungi

14. Fungi
• Eukaroytic organisms
• Non-chlorophyll
• Vegetative growth is through mycelium
Singular = mycelia
• Single thread = Hypha, plural =
(Hyphae)
• Propagate via spores

17. Classification of Fungi
–Zygomycota
–Oomycota
–Ascomycota
–Basidiomycota
–Deuteromycota

18. Oomycota
•Water molds
•Sexual reproduction = Oospores
•Asexual reproduction = Zoospores
•Example: Littleleaf disease

21. Ascomycota – Cup Fungi
• Sexual reproduction = Ascospores are
produced in a sac-like structure called an
Ascus (Always 8 Ascospores / Ascus)
– Apothecia = open
– Perithecia = closed and flask shaped
– Cleistothecia = closed and ornamented
– Hysterthecia = closed and elongated
• Asexual reproduction = Conidia on a
conidiphore
– Synnemata (flask shaped – long)
– Pycnidia (flask shaped – short)
– Spordochia (cushion or padded)

31. Basdiomycota – Gilled fungi
• Sexual reproduction = Basidiospores
are produced on a club-like structure
called a Basidium
• Always 4 spores/basidia
• Asexual reproduction = Conidia on a
conidiphore
– Synnemata (flask shaped – long)
– Pycnidia (flask shaped – short)
– Spordochia (cushion or padded)

38. Deuteromycota
• Sexual reproduction = No known sexual
state = Fungi Imperfecti
• Asexual reproduction = Conidia on a
conidiophore
– Synnemata (flask shaped – long)
– Pycnidia (flask shaped – short)
– Spordochia (cushion or padded)

43. Bacteria
• Single-celled,
prokaryotic
organisms
• Spread via
• wind, rain,
• insects,
• humans

46. Virus
• Protein encapsulated DNA or RNA
• Usually vectored by insects
• Results in yellowing, chlorosis,
wilting, distortion of infected plant

48. Phytoplasmas
• Neither bacteria or virus, naked
protoplasts with a membrane wall
• Vectored by insects
• Results in yellowing, chlorosis, wilting,
distortion of infected plant

50. Parasitic Plants
• Obligate plants that derive their
nutrition from trees
– Leafy Mistletoe
– Dwarf Mistletoe
– Dodder

54. Nematodes
• Non-segmented microscopic worms
• Live in soil
– Feed on root systems
– Vector virus’ & bacteria
• Vectored by insects
– Pinewood Nematode

56. Questions to answer
• 1) Why are fungi the most important disease causing
organisms of the seven types of organisms that cause
disease?
• 2) In western North America what two types of disease causing
organisms are responsible for the majority of forest diseases
• 3) Describe the features of fungi and how they grow and
reproduce
• 4) Describe the difference between true mistletoe and dwarf
mistletoes.
• 5) Describe the features of bacteria and how they grow and
reproduce.
• 6) What are viruses and viroids? Describe how they disperse
and the “typical” symptoms of virus disease in plants.

57. • 7) What is a nematode? What special feature makes this
organism a plant pathogen?
• 8) Describe how you would tell fungi in the Ascomycota,
Basidiomycota, Oomycota, Zygomycota apart?
• 9) Where do the Deuteromycota fit in the classification scheme
of fungi?
• 10) Define the terms: Disease, Signs & Symptoms.
• 11) What are the seven biological agents causing plant
disease?
• 12)What are Koch’s Postulates?
• 13) Describe the disease triangle, the disease square and the
disease tetrahedron and how they can be used to predict
disease.