This is the report from a BSPP Undergraduate ‘Vacation’ Bursary.
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Armillaria is a necrotrophic destructive fungal plant pathogen, commonly called honey fungus. It has an extremely wide host range with no plants being completely immune, allowing it to wipe out a complete garden. Armillaria causes serious damage to the plants it infects resulting in symptoms similar to root rot. There is currently no treatment for the disease with fungicides and removal of infected plants being ineffective and impractical. My project aims to assess the use of saprophytes as a biocontrol agent against Honey fungus for UK gardener use.
For my experiment, we used various saprophytes to help control the disease progression of Armillaria in order to build on their potential as biocontrol agents as seen by other saprophytes like Trichoderma. I looked at four species of saprophytes; Bjerkandera adusta, Trametes versicolor, Pleurotus ostrea and Hypholoma fasciculare. These were selected due to their practical uses being edible and easy to grow for gardeners with a very fast growth rate. These saprophytes were involved in three separate experiments. The first was using strawberry plants which had the four different species of saprophytes added to the soil, along with honey fungus-infected conkers to initiate disease in the plants. Along with these four groups, three controls were made to ensure the experimental design was correct which involved a group with just infected conkers, a group with a non-infected conker and one with just T. versicolor added to the soil. Weekly observations were made over an eight-week period to assess the disease progression of the individuals within the group and by the end of this period, several measurements were taken. These included counting the number of fruit and healthy leaves produced by each plant as well as the weight of the plant and the number of individuals that had mycelium present on their root crown.
Initial observations indicated all controls looked as expected with just infected plants clearly struggling and those with just T. versicolor were the healthiest. In addition, the P. ostrea group appeared to be the healthiest out of the treatment groups and this was later confirmed by ANOVA and Chi-squared statistical tests with P. ostrea having significantly less mycelium on their root crown demonstrating it as being an effective preventative of Armillaria progression. The statistical test also showed the T. versicolor control to be consistently the most significant group and confirmed the original observation of these being the healthiest plants, indicating saprophytes provide benefits to the plant in non-diseased conditions.
In addition to this experiment, investigations were carried out on split agar plates to find out if volatiles were made by any of the saprophytes or Armillaria to control growth rate. With no zones of inhibition observed and no change in growth rate, it was concluded that neither produced chemical compounds to act defensively. Finally, we looked at the physical interactions of the two fungi on normal agar plates and found both continued to grow successfully in the presence of the other, indicating there may not be much competition between the saprophytes and Armillaria.
To conclude my experiments, I could clearly see that saprophytes provide benefits to plants in both normal and diseased conditions with P. ostrea seeming to be the most effective treatment against Armillaria in strawberry plants. By working more in this area and gaining more knowledge on the interaction between saprophytes and Honey fungus, we can begin to improve treatment strategies for this destructive fungal pathogen that are both easily accessible, effective and practical for UK gardeners and therefore reduce plant loss.
I would like to thank my supervisors Megan McDonald and Stephen Hill who have both been a massive help in this project – guiding me in the right direction and allowing me to learn extremely valuable skills in the lab. This has been an incredible experience which has allowed me to work in an exciting and niche area of plant pathology and I am excited to continue my work on Armillaria for my Bachelor’s project. This placement has also led me to be eager to pursue a career in plant pathology upon finishing my University degree.
Freya Sorenti
University of Birmingham
