Getting to the root of the problem
: Understanding and Controlling Armillaria

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

The Agaricomycete fungal root rot pathogen, Armillaria, is important worldwide causing serious losses in forestry, horticulture and agriculture. Historically, soil fumigants were used to control the spread of Armillaria, however, due to negative environmental impacts these have been banned. Current methods of control are laborious and involve removing the entire infected plant including the root system. To explore an environmentally-friendly option for control, this thesis will consider the potential of Trichoderma spp. as biocontrol agents of Armillaria mellea, the most virulent species of Armillaria in the UK.

A collection of 40 endophytic Trichoderma spp. were isolated from the roots of healthy plants in areas where A. mellea infection was endemic. All Trichoderma isolates were assessed for antagonism against A. mellea in challenge assays, where almost unanimously, Trichoderma overgrew Armillaria colonies. In dual-culture assays five out of eight Trichoderma isolates eliminated Armillaria growth and in wood, two Trichoderma isolates eliminated Armillaria growth completely. Seven Trichoderma isolates protected plants from Armillaria Root Rot (ARR) when screened in strawberry plants. These isolates were further tested in privet plants, where two isolates of Trichoderma atrobrunneum were identified as potential biocontrol agents against ARR.

Although a number of Armillaria species genomes have been published, we have a poor understanding of gene function in Armillaria, particularly regarding virulence. Seven candidate genes with homologs to virulence genes in model fungal plant pathogens were chosen for study. Promoter:GFP fusion transgenic lines of A. mellea were created, however poor rate of fluorescence combined with autofluorescence made gene function assessment difficult. RNA expression profiles were assessed for candidate genes on mycelial tissue from cultures and mature fruiting bodies. Results suggest that signaling-related genes, effectors and some SSPs were constitutively expressed.

Together this shows that whilst Armillaria infection is poorly understood, the future prospects to control ARR are positive.
Date of Award24 Jun 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAndy M Bailey (Supervisor), Gary D Foster (Supervisor), Jassy Drakulic (Supervisor) & Matthew Cromey (Supervisor)

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