| Summary: | During a survey of oomycetes in ornamental plants carried out at the University of Aberdeen in 2014–2015, <i>Pythium kashmirense</i> was isolated from a specimen of <i>Viburnum plicatum</i> ‘Lanarth’, the first report of this oomycete in the UK (and in Europe). Pathogenicity of a <i>Py. kashmirense</i> isolate was examined using a range of plant species. Inoculations were carried out under controlled conditions in the absence of other <i>Pythium</i> and <i>Phytophthora</i> species, on <i>Glycine max</i> (soya bean), <i>Phaseolus vulgaris</i> (common bean), <i>Lupinus angustifolius</i> (blue lupin), <i>Cucumis sativa</i> (cucumber) and <i>Viburnum opulus</i>. The majority of inoculations caused pre-emergence damping-off, as well as seed rot and root rot. In the in vitro assays, germination rates (%) of soya bean and blue lupin seeds were less than 50%; in the in vivo inoculations on plants, over 50% of soya bean, blue lupin and common bean plants died; in contrast, cucumber plants showed lower susceptibility in pathogenicity tests, with an approximately 80% germination rate in in vitro tests, and 25% dead plants in the in planta inoculations. Inoculations carried out on root systems of <i>Viburnum opulus</i> caused severe necrosis and root rot. Little research was previously conducted on pathogenicity of <i>Py. kashmirense</i> and its relationship with losses in crop yield and quality. The present study showed varying virulence on the different plant species tested after inoculation with <i>Py. kashmirense</i>. Despite the lack of clear host specialization, infection by <i>Py. kashmirense</i> decreased seedling survival and health of plants in a range of important agricultural and ornamental plant species.
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