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

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

Biotic Disorders

• Plant Pathology - Pathogens, Parasites, Saprophytes, Symbiosis

– Pathogen:

– Parasite:

– Saprophyte:

– Symbiosis:

– Obligate:

Biotic Disorders

• Plant Pathology - Pathogens, Parasites, Saprophytes, Symbiosis

– Facultative:

– Obligate parasite:

– Facultative parasite:

– Obligate saprophyte:

– Facultative saprophytes:

Disease Triangle & Tetrahedron

Host

Pat

ho

gen

Environment

Tim

e

Disease Square

Biotic Disorders

• Signs and Symptoms of Disease

Signs

Symptoms

Biotic Disorders

• Symptoms of Disease

– Necrosis

– Decay

– Cankers

– Leaf spots

– Wilts

Biotic Disorders

• Symptoms of Disease

– Blights

– Hypertrophy

– Atrophy

– Physiology

Koch’s Postulates

Robert Koch 1843-1910

Proved Bacillus anthrax was responsible for disease in animals and humans

Noble Prize Winner 1905

Koch’s PostulatesProof 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

Biotic Disorders

• Types of biotic agents

– Fungi

Fungi

• Eukaroytic organisms

• Non-chlorophyll

• Vegetative growth is through mycelium Singular = mycelia

• Single thread = Hypha, plural = (Hyphae)

• Propagate via spores

Classification of Fungi

–Zygomycota

–Oomycota

–Ascomycota

–Basidiomycota

–Deuteromycota

Oomycota

•Water molds

•Sexual reproduction = Oospores•Asexual reproduction = Zoospores

•Example: Littleleaf disease

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)

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)

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)

Bacteria

• Single-celled, prokaryotic organisms

• Spread via• wind, rain,• insects, • humans

Virus

• Protein encapsulated DNA or RNA• Usually vectored by insects• Results in yellowing, chlorosis, wilting,

distortion of infected plant

Phytoplasmas

• Neither bacteria or virus, naked protoplasts with a membrane wall

• Vectored by insects

• Results in yellowing, chlorosis, wilting, distortion of infected plant

Parasitic Plants

• Obligate plants that derive their nutrition from trees – Leafy Mistletoe– Dwarf Mistletoe– Dodder

Nematodes

• Non-segmented microscopic worms

• Live in soil– Feed on root systems– Vector virus’ & bacteria

• Vectored by insects – Pinewood Nematode

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.

• 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.