Plant Pathology - What's wrong with this plant?

What is a “normal” plant?

A plant not limited by stress or disease.

A plant that can fully express its genetic potential.

A plant that can carry out essential physiological functions.

What are the different areas a plant may become compromised?

1. Leaf

   1. Photosynthesis, gas exchange, evapotranspiration

2. Roots

   1. Nutrient & water uptake

3. Stem

   1. Xylem - water transport

   2. Phloem - sugar (photosynthate) transport

4. Flowers and fruits

   1. Reproduction and yield

How is plant disease defined?

Suboptimal growth due to a persistent and continuous disturbance, either biotic (pathogen) or abiotic (environment).

What is the difference between plant disease and plant injury?

Time - plant disease develops, while plant injury happens.

When were microscopes developed?

1600s

What is spontaneous generation?

The belief that disease produced pathogens, not the other way around. Belief held until mid 1850s.

When was Germ Theory developed?

1850-1920. Developed & accepted that specific microorganisms cause specific disease.

What year did plant pathology as a science emerge?

1840. M.J. Berkeley linked fungi to plant disease.

When was experimental proof for causation developed for fungi?

Mid-1800s, Anton de Bary demonstrated that specific fungi cause specific disease

What are Koch’s Postulates?

A set of criteria to establish a causal relationship between a specific microorganism and a specific disease.

What are the 4 criteria of Koch’s Postulates?

1. The suspected pathogen is consistently associated with a specific disease

2. The pathogen is isolated in pure culture and characterized

3. The disease is reproduced in a healthy plant after inoculation

4. The same pathogen is re-isolated from the inoculated plant

What is a symptom?

The plant’s responses to disease

What is a sign?

The physical presence of the pathogen

What is the Disease Triangle?

Host

Pathogen

Environment

What are the 2 main categories of plant disease?

Abiotic

Biotic

What are abiotic diseases?

• Caused by non-living factors

• Does not spread from plant to plant

• No pathogen present

• First consideration when diagnosing

• Examples: heat, nutrient deficiency, wildfire, water stress

What are biotic diseases?

• Caused by pathogens (living organisms)

• Can spread between plants

• Can affect any plant tissue

• Vary in their host range

What are the 5 mechanisms impacted/involved in plant disease?

1. Enzyme activity - degradation of host tissue

2. Toxin production

3. Alteration of plant growth regulators

4. Redirection of host resources

5. Mechanical blockage (eg. vascular obstruction)

What are the 2 ways pathogens can get their nutrients?

1. Parasites: get their nutrition from a living host

2. Saprophytic: get nutrition from dead organic material

What is an obligate pathogen?

One that must have a living host to survive.

What is a facultative pathogen?

One that can survive with or without a living host.

What is a biotroph?

Feeds on living tissue

Usually obligate parasites

What are necrotrophs?

Kills host tissue and feeds on dead material

Usually facultative and less host-specific

Where do viruses replicate?

They are obligate intracellular pathogens, meaning they replicate inside of the host cell .

How do viruses disrupt normal plant functions?

They utilize host cells for their replication. They also disrupt plant metabolism and development through the introduction of foreign genetic material.

How can bacteria cause plant disease?

1. Blocking vascular tissue

2. Producing enzymes and toxins

3. disrupting normal plant function

Do bacteria require a host cell to reproduce?

No

What are parasitic higher plants?

Plants that obtain water and nutrients from other plants.

What are parasitic higher plants that cannot photosynthesize called?

Holoparasites

What are parasitic higher plants that can photosynthesize called?

Hemiparasites - but still rely on host for nutrients & water

How much estimated monetary loss is there each year due to plant pathogens?

Hundreds of billions of dollars

Why is it important to understand the disease cycle?

Every pathogen and host plant have a life cycle. Understanding how they interact can pinpoint when intervention is most effective.

What are the 2 types of disease cycles in plants?

1. Monocyclic -

   1. infection —> survival —> primary inoculum —> dispersal of inoculum —> infection court —> infection

2. Polycyclic -

   1. infection —> survival —>primary inoculum —> dispersal —> infection court —> infection —> secondary inoculum….

What is primary inoculum?

The stage of the pathogen that initiates disease

What is infection court?

Plant tissues or sites susceptible to infection

What is the incubation period?

The time lag between infection and symptom expression

What is the secondary inoculum?

The inoculum produced by the infected plant that spreads to another host

What is a disease management strategy that focuses on the plant (versus the pathogen)?

Protection of the plant - IPM

What are disease management strategies that focus on the pathogen?

1. Avoidance

   1. Selecting plant site or timing to minimize exposure

2. Exclusion

   1. Quarantines, pathogen-free planting materials

3. Eradication

   1. Removal and destruction of infected material