Oak powdery mildew and tree health in the Celtic rainforest

Aberystwyth University

Oak powdery mildew (PM), caused by the ascomycete fungus Erysiphe alphitoides (alongside its close relatives E. hypophylla and E. quercicola), is an invasive disease which was introduced to Europe from the USA in ca. 1900. It has been linked to the UK oak dieback episode a century ago, but presently is not associated with high tree mortality. However, the damage it causes to leaf tissues and reduced fitness of trees can make them more susceptible to other disease, making PM a key contributing factor in decline diseases. Also of concern is the fact that the disease is exacerbated by warmer summers and the potential that PM may check or kill regrowth of oak shoots from pollards or coppice stools. The recent review undertaken by Action Oak by Quine et al. (2019; Action Oak Knowledge review: an assessment of the current evidence on oak health in the UK, identification of evidence gaps and prioritisation of research needs) has assessed the current state of knowledge on this disease and this proposal addresses several of the knowledge gaps which were identified.

This proposal aims to investigate the distribution and spread of oak PM in oak woodlands across Wales, with a focus on upland Quercus petraea -dominated ‘Celtic rainforest’ habitats.

Project objectives:

1) Undertake a survey of 12 oak woodland habitats in Wales to assess the distribution and severity of PM and collect leaf samples to confirm identity of the pathogen species. The field sites will comprise Celtic rainforest woodlands, lowland Q. robur dominated woodlands and intermediate sites (where restoration projects are underway).

2) Assess using seedling trials the susceptibility of different genotypes of Q. petraea and Q. robur to PM disease under controlled conditions (glasshouse trials). This will identify whether oaks of different species and provenance are all equally susceptible to oak PM under standard conditions, and whether there is variation in pathogenicity of oak PM pathotypes from across Wales.

3) To survey the fungal diversity and ecology of these habitats using DNA metabarcoding to examine the mycobiota of healthy/diseased oak leaves, soil (where resting propagules may persist) and air (to capture pathogen propagules).