First record of Plasmopara obducens (Impatiens downy mildew) in United Kingdom
In June 2003, a sample of Impatiens walleriana from southern England showing symptoms of downy mildew was examined. Infected leaves appeared paler green than normal, with a white, downy growth developing on lower surfaces. Symptoms were initially inconspicuous but lower leaf surfaces quickly became covered with mycelial growth and premature leaf fall was common. Stunting of plants and poor flowering were also observed. Plant collapse could be very rapid, especially under humid conditions, resulting in up to 80% losses. The pathogen was identified (morphology, DNA sequencing) as Plasmopara obducens. Following this initial discovery, the NPPO of UK carried out a survey of growers. Further findings of P. obducens were made on a range of Impatiens cultivars. However, no infection was found on wild impatiens growing around nurseries.
This is the first report of P. obducens in UK. It is reported that this pathogen has been found in other parts of Europe (without further details) and in Canada, USA, Guatemala, Central Asia
(without further details), China, India, Korea and Russia. It is also pointed out that statutory action is being taken in UK against this disease.
Sources
Lane CR, Beales PA, O’Neill TM, McPherson GM, Finlay AR, David J, Constantinescu O, Henricot B (2005) First record of Impatiens downy mildew (Plasmopara obducens) in the UK.
New Disease Reports Volume 10 (August 2004 - January 2005)