Tag Archives: Tom Hsiang

Using Plant Defence Activators To Control Turfgrass Disease: Conclusion

By Tom Hsiang, PhD, Paul H. Goodwin, PhD, and Alejandra M. Cortes-Barco, M.Sc.

Regarding the activity of the defence activator Civitas, the conclusions found were:
● minor direct effects on fungi;
● suppressive effects against diseases in lab and field tests;
● primes defence response genes for greater and faster expression after infection; and
● relies on an ISR-based mode on gene expression analysis when compared to gene expression after application of butanediol—a known ISR activator.

A wide and diverse range of compounds can activate SAR, ISR, and other forms of induced resistance. These compounds may be naturally occurring in plants or microbes or can be entirely synthetic compounds that affect some part of pathways which are involved in functions ranging from the detection of pathogen-produced molecules by receptors on the plant cell membrane up to factors that bind to deoxyribonucleic acid (DNA) and affect expression of defence-related genes in the plant nucleus.

While the list of activators continues to grow, it remains a challenge for disease management to adapt these compounds into practical materials for commercial use. Important desirable qualities for their practical application are similar to those of synthetic fungicides, such as:
● stability;
● shelf-life;
● consistency;
● cost; and
● ability to perform under various favourable and unfavourable conditions.

However, as more defence activators are discovered, the probability increases that some will have the qualities needed to replace or complement the current pesticides being used against plant pathogens.

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Using Plant Defence Activators To Control Turfgrass Disease: Mode Of Action Of Civitas

Amended agar assay was used to test the sensitivity of different fungal species to the isoparaffin mixture (active ingredient in Civitas), which is used at five per cent in the field. Photo courtesy Tom Hsiang

By Tom Hsiang, PhD, Paul H. Goodwin, PhD, and Alejandra M. Cortes-Barco, M.Sc.

One of the features of a resistance-inducing compound is it should have a weak or no direct effect on the pathogen. Sixteen different turfgrass pathogens were tested on culture media amended with 0 to 20 per cent Civitas and there was slight growth inhibition observed. However, in longer-term growth tests, this inhibition was found to disappear after 10 days, since growth rates after that time were similar between amended media and non-amended controls.

The product was sprayed onto turfgrass in the field, and found to have significant activity against various turfgrass diseases with almost full disease suppression in some cases.

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Using Plant Defence Activators To Control Turfgrass Disease: Activated Resistance Against Turfgrass Pathogens

By Tom Hsiang, PhD, Paul H. Goodwin, PhD, and Alejandra M. Cortes-Barco, M.Sc.

Control of turfgrass diseases is notorious for the large amounts of pesticides used. In high-maintenance turfgrass systems such as golf courses, in addition to the strict esthetic standards, plant tissue is frequently removed and new growth needs constant re-protection. Although fungicides are very effective for controlling most turfgrass diseases, there is a market for alternatives. New compounds have been developed that cause plants to be more disease-resistant. Important defining characteristics of such compounds include:
● the plant is directly affected by the compound;
● the compound may have a weak or no effect on the pathogen; and
● the compound causes systemic activation of resistance.

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Using Plant Defence Activators To Control Turfgrass Disease: Activated Resistance Against Plant Diseases

Figure 1: A diagrammatic representation of systematic acquired resistance (SAR). Image courtesy Tom Hsiang

By Tom Hsiang, PhD, Paul H. Goodwin, PhD, and Alejandra M. Cortes-Barco, M.Sc.

Activated, acquired, or induced resistance is a physiological state in which environmental, chemical, or biological stimuli increase a plant’s defences against subsequent pathogen or insect pest attack. During induced resistance, the activating agent—often called a ‘plant defence activator’—is recognized by the plant or stimulates a part of a recognition-signalling pathway. The pathway(s) eventually promote the expression of genes resulting in activation of defence mechanisms, such as production of antimicrobial proteins. The enhanced resistance is expressed locally at the site of infection, or, in some cases, systemically throughout the plant.
Two major forms of this type of activated resistance are generally described: systemic acquired resistance (SAR) (Figure 1), and induced systemic resistance (ISR) (Figure 2).

Read the full article: Using Plant Defence Activators To Control Turfgrass Disease

Using Plant Defence Activators To Control Turfgrass Disease

Photo courtesy Tom Hsiang

By Tom Hsiang, PhD, Paul H. Goodwin, PhD, and Alejandra M. Cortes-Barco, M.Sc.

Plants are known for their many natural defence mechanisms against stresses, including those caused by diseases. Unfortunately, under intensive plant maintenance systems, these natural mechanisms are often unable to guard against outbreaks without significant economic loss. However, there are chemicals that have been observed to stimulate the natural resistance pathways in plants, although most research has been conducted on broadleaf plants. These compounds generally do not have a direct antifungal activity, but act by triggering existing defence mechanisms of the plant.

Read the full article: Using Plant Defence Activators To Control Turfgrass Disease