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New DNA techniques to diagnose tree diseases

Ever wondered why seemingly healthy trees drop their branches or even topple over without much warning, sometimes resulting in human injuries and significant property damage?

Apart from environmental and physiological reasons, diseases are a major cause of such tree failures. Some of the most common and aggressive trunk and root rot diseases in the Sydney region are caused by various wood decay fungal genera, such as Phellinus, Ganoderma and Armillaria. These fungal pathogens colonise internal plant tissue causing internal decay, often without any obvious external symptoms. The diagnostic basidiocarps (brackets and mushrooms) are usually not formed until the disease and decay is in its advanced stages. Unfortunately disease diagnosis at this stage is often too late for tree health management as the structural integrity of the trees may already be severely compromised. These pathogens can infect almost all tree species, creating a major problem in our urban streets, parks and gardens.

Collaborating with arborists, the Plant Disease Diagnostic Unit at the Royal Botanic Garden, Sydney has developed new ways to detect these tree pathogens based on cutting-edge DNA technologies. Small amounts of drill dust obtained from tiny drillings of trunk tissue containing the pathogen are sufficient for DNA testing, using techniques akin to those used in human forensic studies. Total DNA is extracted from the tissue sample in the laboratory and DNA finger-prints or bands specific to various fungal pathogens are visualised.

Because these DNA-based techniques are highly sensitive and pathogen-specific, the new pathogen detection protocols provide powerful means of early and precise disease diagnosis which facilitates best practice tree management, hence reducing the risks of disastrous outcomes.

For more information, please call Matt Laurence (Mon-Fri) on 9231 8186 or Edward Liew on 9231 8189. Please also refer to the Plant Disease Diagnostic Unit web pages.

Edward Liew
Manager Plant Pathology
The Royal Botanic Garden Sydney

Figure-1
Figure 1: Drill dust obtained from a tree trunk infected with a bracket fungus.

Figure-2
Figure 2: Drill dust in an Eppendorf tube ready for DNA extraction.

Figure-3
Figure 3: DNA gel photo showing specific bands which indicate the presence or absence of specific trunk rotting fungal pathogens.