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Associations of Armillaria root rot, Trichoderma endophytes and host plants in UK gardens

Jassy Drakulic: Royal Horticultural Society

<div>Armillaria root rot affects hundreds of plant species and can cause the death of mature trees in parks and gardens. Management advice for gardeners is to remove infected root systems and prevent below ground spread with impermeable barriers. This approach is costly, labour intensive, difficult to perform in most gardens, and thus often unsuccessful. Our three-year survey of UK gardens found that the vast majority (83.1%) of plant deaths by <em>Armillaria</em> spp. are due to the aggressive pathogen <em>A. mellea</em>. <em>Ligustrum</em> was the most commonly reported host, highlighting the threat from <em>Armillaria</em> to hedges, and 14 new hosts were recorded that extend the already broad host range. Garden planting choices are greatly restricted if species susceptible to Armillaria root rot are avoided. <em>Trichoderma</em> endophytes were studied for their potential to improve host resilience and promote growth during establishment when root systems are at greatest risk of succumbing to <em>Armillaria</em> infection. Introduction of suitable isolates to susceptible plants would empower gardeners to replant <em>Armillaria</em>-infected beds. Susceptible hosts that had evaded disease from infection foci at RHS Garden Wisley were sampled. Endophytes from these root systems were cultured, identified and screened for beneficial effects on common garden plants (<em>Rosmarinus officinalis</em> and <em>Thymus vulgaris</em>). <em>T. atrobrunneum</em> was isolated most frequently, and has shown improved host growth and <em>in vitro</em> inhibition of <em>A. mellea</em>.</div>