Effect of allicin (garlic extract) on the growth of Armillaria mellea and A. gallica

RHS project team

Dr Liz Beal

Start date

09/01/2011 15:01:22

End date

09/01/2014 15:01:30

The problem

Honey fungus is the most common disease found by the RHS advisory service in UK gardens (Henricot 2011). The disease infects the roots of trees and shrubs and either kills the plant outright by killing the roots and root collar, or the living tree may blow over due to the root system being weakened by the pathogen.

There are few controls currently available to UK gardeners (or professionals). Our current advice is to remove infected plants including roots to minimise available inoculum in the garden. It would be useful if other control methods were available to gardeners. Allicin (garlic extract) has long been known for its anti-fungal and anti-bacterial properties but little research has been undertaken to examine its action on honey fungus.

Approach

The project examines the action of allicin on the growth of honey fungus mycelia and rhizomorphs on agar plates. Two Armillaria species will be examined, A. mellea and A. gallica. These species were chosen as they were found to be the two most common species in UK gardens, making up almost 97% of cases found during a recent RHS survey (Beal et al 2011). It is widely accepted that A. mellea is highly pathogenic. Whereas, A. gallica is thought to be less pathogenic, infecting only those hosts which have been subjected to some sort of stress. It will be interesting to know if they behave differently in the presence of allicin. Fifty isolates per Armillaria species were chosen to ensure virulence differences due to intraspecies’ variation were assessed. Honey fungus isolates were chosen to cover a broad spectrum of the UK and from at least 25 different host plants per Armillaria species.
 
Allicin will be incorporated into agar plates at five different concentrations (0, 20, 30, 50 and 100 ppm) and growth rates measured periodically over 21 days. From this data EC₅₀ values can be calculated. EC₅₀ values represent the concentration of allicin required to inhibit Armillaria growth by half when compared to growth in the absence of allicin (control). From this data we can see whether allicin has any potential to control honey fungus, and whether it is a suitable candidate for further experiments in the field.

Benefits to gardeners

There is a lack of methods to control honey fungus in gardens. This study examines the effect of allicin (garlic extract) on the growth of honey fungus (Armilllaria spp.) isolates on agar plates and considers its potential as a possible method of control.

Further information

Advice on honey fungus

Armillaria survey

Behaviour of severed rhizomorphs of Amillaria mellea and A. gallica in growing media

Studies on the pathogenicity of Armillaria spp.

References

Beal, L., Burdon, I., Denton, J. and Henricot, B. 2011: Preliminary assessments to determine the potential risk of Armillaria gallica to healthy plants. Proc. IUFRO WP7.02.01 Root and Butt Rot of Forest Trees, Firenze, September, 4^th-10^th 2011

Henricot, B. 2011: Honey fungus. The Garden. November issue, 58-59.