Learning Objectives

It is expected that after watching the presentation and lab videos you should have learnt the following:

• Analyze the concept of “healthy forest”.
• Explain the role of fungi in forest.
• Explain the difference between the terms abiotic, decline and biotic regarding forest diseases.
• Describe the difference between stand and tree level symptoms of diseases.
• Differentiate between the different categories of forest pathogens.
• Describe how to recognize and identify pathogens.
• Describe the symptoms and effects of white and brown rot decay fungi.
• Discuss Armillaria root disease and white pine blister rust.

Module Resources

Presentations

Introduction to Forest Pathology
Dr. Richard Hamelin explains that forest health depends on user expectations, and the spatial and/or temporal scale at which forest is examined. Disease, the reaction of the tree to the biotic or abiotic disturbance, has numerous positive and fewer negative roles in forest. Forest pathogens, biotic agents which can cause the disease, can be foliar, stem, root, mistletoe, white and brown rot, native or introduced organisms.

Pathology in the Forest
In this video, Dr. Hamelin examines forest health. Starting from the stand level, he points out symptoms of disease problems in the forest. Inside the forest there are infection centres; tree level examination reveals several signs and symptoms of laminated root disease: root balls, delamination of lignon and the mauve-coloured mycellium of Phellinus weirii. Is this forest healthy? The disease centre makes for openings in the stand canopy which allows for regeneration; the white decay fungus that breaks down the log plays an essential role in nutrient cycling.

Pathology in the Lab: Introduction
It is not always possible to determine the pathogenic causal agent of a disease by looking ath the symptoms found in the forest; determination needs to take place in the laboratory.

Pathology in the Lab: Pathogen Isolation
Padmini demonstrates how to isolate the causal agent of a canker. Working in a sterile environment, she obtains a small piece of the canker and places it on growing medium in a petri dish. Isolation involves several cycles of sampling and sub-culturing until a pure culture of the pathogen, (Septoria musiva), is obtained. She also shows the first step in DNA identification of a pathogen excised from a leaf spot of the pathogenetic material for testing.

Pathology in the Lab: DNA Analysis
Stephanie demonstrates the identification, through molecular biology, of the pathogen that caused the leaf spots Padmini excised in the previous video. The extraction of the DNA involves a long protocol of initiating grinding then centrifuging and filtering the sample. The resultant pure DNA sample is put into a PCR (polymerase chain reaction) machine to generate millions of copies and identified using agral gel for visualization of the DNA.

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• Tree Insects and Diseases of Canada’s Forests
• Agrios, G. 2011. Plant Pathology. 6th ed. Academic Press.
• Forest and Shade Tree Pathology by Dr. James Worrall, Forest Pathologist, USDA Forest Service, Rocky Mountain Region.
• Forest Pathology and Wood Microbiology Research Laboratory of Dr. Robert Blanchette, U. of Minnesota.