Investigating the potential use of endophytes to induce resistance to honey fungus

RHS project team

Helen Rees, Jassy Drakulic, Matthew Cromey

Start date

18/09/2017 00:00:00

End date

18/09/2020 12:00:00

Keywords

Armillaria, honey fungus, biological control, laboratory, field trials

The problem

Armillaria spp., commonly known as honey fungus, is a devastating fungal pathogen found worldwide and is a big problem in UK gardens (RHS, 2018).

At present, control of the disease is very difficult. Chemical controls are either ineffective or are banned due to negative environmental impacts (Ristaino and Thomas, 1996). Cultural control methods, such as digging out root systems or creating trenches around infected plants, are used with some success against Armillaria infections but they are very labour intensive (Fox, 2000). 

In a garden situation with several hosts that are susceptible to honey fungus infection, not every susceptible host will die. Likewise, different gardens with the same species of Armillaria in their soils experience varied numbers of plant deaths. What causes these different outcomes is not understood, and one possible explanation involves the makeup of the fungi that colonise the plant roots. Beneficial fungi, including Trichoderma species, have the potential to out-compete invading Armillaria species - they act as biological control agents, or prime plant defence systems so are better able to exclude incoming pathogens.

There are currently no effective biocontrol options available to act against Armillaria root rot. Some studies have highlighted that there is potential for Trichoderma species fungi to act as biocontrol agents of Armillaria species (Kwaśna et al., 2004), and Trichoderma species are an effective biocontrol agent of a number of diseases including Botrytis cinerea which affects soft fruits (i.e. strawberries) (Freeman et al., 2004). 

Approach

Research Question 1: Does the introduction of Trichoderma endophytes into plant roots improve host plant resilience so as to protect against Armillaria root rot?

Trichoderma endophytes were isolated from the roots of healthy plants located in beds where other plants had succumbed to Armillaria.

We hypothesise that the roots of plants that are able to remain healthy when growing in soils where Armillaria is known to be present are colonised with beneficial fungi, including species of Trichoderma, which offer protection to their host plants against invading Armillaria.

To identify isolates of Trichoderma most beneficial to host plants, all isolates collected by the RHS are currently being screened in strawberries to look for increased plant vigour. Selected isolates will be challenged in plants with Armillaria to test whether the disease severity of Armillaria is reduced in the presence of the Trichoderma. 

The interaction between Armillaria and Trichoderma isolates will also be assessed. Tests in the lab will look at how Armillaria and Trichoderma interact together and whether antibiotics are produced by Trichoderma spp. which could actively suppress Armillaria invasion.

Research Question 2: What genes are involved in the pathogenicity of Armillaria?

The publication of the genomes of Armillaria species has highlighted some genes of interest which might be related to pathogenicity. The aim is to investigate their function during infection on hosts to help understand how Armillaria infects host plants.

Aims

The aim of this project is to investigate the potential of Trichoderma species as a beneficial root endophyte to protect host plants against Armillaria. The project also aims to study potential genes involved in pathogenicity of Armillaria.

Benefits to gardeners

As the most common plant diseases enquiry at the RHS relates to Armillaria (RHS, 2018), it's a hugely important and crucial disease for gardeners to understand and protect their gardens from.

This project will shed light on the molecular mechanisms behind Armillaria root rot, as well as the role of the microbiome in determining the outcome of Armillaria infection.

In both cases, the information gained will improve the advice given to gardeners managing Armillaria infections.

Moreover, it has the potential to identify a new biological approach to managing the disease in gardens.

Summary of results

Research for this project is ongoing. Once result have been analysed they will be shared on this page. 

Advisory information

• Honey fungus disease profile
• Managing honey fungus outbreaks
• Identifying honey fungus: making a spore print

References

Fox, R. T. V. (2000). Cultural Methods to Manage Armillaria. In: Armillaria Root Rot: Biology and Control of Honey Fungus, 1st ed, Andover: Intercept Ltd.

Freeman, S., Minz, D., Kolesnik, I., Barbul, O., Zveibil, A., Maymon, M., Nitzani, Y., Kirshner, B., Rav-David, D., Bilu, A., Dag, A., Shafir, S. and Elad, Y. (2004). Trichoderma biocontrol of Colletotrichum acutatum and Botrytis cinerea and survival in strawberry. European Journal of Plant Pathology, 110 (4), p.361–370.

Kwaśna, H., Łakomy, P. and Mallett, K. (2004). Reaction of Armillaria ostoyae to forest soil microfungi. Forest Pathology, 34 (3), p.147–162.

RHS. (2018). Top 10 pests and diseases for 2016. [Online]. Available at: https://www.rhs.org.uk/advice/advice-blogs/help-and-advice/March-2017/2016-pest-disease-top-10 [Accessed: 2018].

Ristaino, J. B. and Thomas, W. (1996). Agriculture, Methyl Bromide, and the Ozone Hole. Can we fill the gaps? Plant Disease, 81 (9).