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O26 Webber

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Published on November 24, 2008

Author: bongsoopark

Source: slideshare.net

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2008 Phytophthora Workshop in Italy
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Persistence of Phytophthora kernoviae and P. ramorum on infested sites: impact on disease management Joan Webber, Forest Research 3rd International Phytophthora Workshop

P. kernoviae / P. ramorum Both apparently introduced invasives in Britain Both aerial Phytophthoras which cause foliar/shoot symptoms on rhododendron Rhododendron is the UK ‘bay laurel’ Both cause bleeding lesions on trees, mainly beech (Fagus sylvatica) Both thrive under similar climatic regimes typical of Cornwall in south west England, so the majority of outbreaks are there

Disease outbreaks: 2002/03 - 08 England, Scotland and Wales Pathogen Nurseries/ retail Managed/ plant sales unmanaged P. ramorum 611 (498*) 224 (68*) P. kernoviae 4 (3*) 55 (2*) Total 615 (501*) 279 (70*) * eradicated outbreaks Data derived from Defra Consultation document 2008

XXXXXX Distribution of Pr Distribution of Pk XX XX XXXXXX

Current measures in the UK • EU emergency measures apply to Pr – eradication of infection in nurseries – containment/eradication of infection in natural and semi-natural environments • Similar measures apply to Pk – containment or eradication via the removal of infected understorey plants as the majority of outbreaks are in woodlands with a dense understorey of R. ponticum

Impact of rhododendron eradication over 1-3 years • Time frame for persistence in naturally infected leaves of rhododendron? • Persistence in litter and soil? • Regrowth and re-infection of the rhododendron?

How long does inoculum persist?

Persistence of Pk inoculum Naturally infected leaves put into bags and air suspended or put in litter layer

Survival of Pk in naturally infected leaves: 2005 - 06 Air exposed Litter embedded 100 90 80 % leaves with Pk 70 60 50 40 30 20 10 0 0 1 2 3 4 5 6 8 12 Month

Deterioration of leaves over in the litter layer 3 months 9 months 6 months 12 months

Survival of Pk in naturally infected leaves: 2006 - 07 Air exposed Litter embedded 100 90 80 % leaves with Pk 70 60 50 40 30 20 10 0 0 1 2 3 4 6 8 10 12 Months

Survival of Phytophthora in naturally infected leaves: 2006 - 07 45 P. kernoviae P. citricola 40 35 30 % recovery 25 20 15 10 5 0 0 1 2 3 4 6 8 10 Months

Survival of Pr in naturally infected leaves: 2006 - 07 100 % leaves with P. ramorum 90 Air exposed Litter embedded 80 70 60 50 40 30 20 10 0 0 1 2 3 4 6 8 10 12 Months

Pre and post R. ponticum removal in a Pk infested woodland 80 Litter Soil Percent Pk positive samples 70 60 50 40 30 20 10 0 Pre-treatment Post-treatment Post-treatment (Sept '04) (Sept '05) (Sept ’07)

What happens to inoculum……… ◄ Re-sprouting from rhododendron stumps with infection Recruitment of new ► rhododendron seedlings

Seedling Foliage Soil Roots 1 2 Impact of persistent Pk inoculum 3 4 on rhododendron recruitment 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Fichtner et al., 2008: APS

Conclusions • Both Pr and Pk are proving to be difficult to eradicate from infected natural or semi- natural environments – eradication process must involve litter removal – but persistence is extended and signs of disease by Pk return after more than 3 yr following eradication – additional issue of asymptomatic infection of rhododendron roots by Pk • Is it worthwhile? – removing the infected rhododendron does safeguard trees in woodlands from Pk infection – reduces inoculum and therefore likely to reduce the opportunities for Pk to get into the nursery trade – consultation on ‘is it worthwhile’? www.defra.gov.uk/corporate/consult/phytophthora-ram- kern/index.htm

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