Undergraduate Student Report 2022

The effects of mycorrhizal products on the virulence of Armillaria mellea

Lottie Goodman, RHS Wisley

Fungus in petri dishThis was a 10-week project researching the effect of three different mycorrhizal treatments on the virulence of Armillaria mellea. A. mellea causes Armillaria root rot (ARR), and is named as one of the most destructive fungal pathogens. It damages plantations, orchards and forests, and has been the top reported disease at the RHS for the last 20 years. It is therefore of high importance to research methods of control. Mycorrhizal treatments were tested as it was hypothesised that adding these products would act as a form of preventative control. Mycorrhiza improve plant health and could therefore increase the ability of the plant to defend itself against the disease.

To test this, we used strawberry and privet as hosts for ARR. These were used as they are very susceptible to the disease and so would show disease symptoms and succumb to the disease quickly. We created five different treatment types. Treatment 1=negative control (no A. mellea), 2=positive control (only A. mellea), and 3, 4 and 5 were inoculated with A. mellea and the mycorrhizal treatments Rootmax, Rootgrow, and Rootmore, respectively. The treatments were inoculated with the disease by inserting a hazel billet colonised with A. mellea into the plant pot.

Fungal fruitbodies with strawberry plantsTo measure the degree of virulence, we measured the growth of the plants every week and extracted the DNA from the strawberry root collar to assess for the presence of A. mellea DNA. The strawberries were measured on the basis of the number of leaves and flowers, length of largest leaf, and the colour. The privets were measured on the length of the largest shoot, length of the largest leaf, and the colour. These measurements were statistically analysed in relation to the treatment they had and the environment they were grown in. Over the course of the 10 weeks we also did work on optimising the primers and DNA concentration for PCR.

My results showed that while treatment did significantly influence many of the measurements of growth, it was unlikely to be due to the influence of A. mellea inoculation. The qPCR of the DNA extraction showed no presence of A. mellea DNA. Additionally, the two positive and negative controls showed no significant differences in growth, demonstrating that the inoculation did not have an effect. The differences in growth came primarily from the mycorrhizal treatments. The treatment inoculated with Rootmax was significantly smaller than the other two mycorrhizal treatments and also smaller than the controls. Interestingly, we also found that there was significantly higher numbers of A. mellea-colonised hazel billets with remaining mycelial fans in the Rootmax treatment, compared to other treatments. We have learned from our results that the growth period was not long enough for disease to occur and that the DNA extraction method needs to be improved.

Strawberry plants in potsFrom this project I have learned about and practised a broad range of scientific skills. I have had an opportunity to impact the design of the experiment, and been taught many fundamental lab skills. I have also been able to do data analysis using specialist software and practise interpretation of results. These skills will be directly transferable to my future research projects, and have provided me with skills and experience that I was previously lacking. The project in general has increased my confidence and understanding of scientific thought and process, and I’m very grateful to have been given the opportunity. 

Lottie Goodman was supervised by Dr Jassy Drakulic,  RHS Wisley.